Nit sieiegeie . ‘ ; ayetmt~eienh ee prey aren fe lecns mime et etry adel dek bento ek Sere epele eleimisie er ete tere minieletaiee/Pisininiel aie Aelia eiticie PIMIE He whe (etehete +19 = reretele See ei Oho where Sd Si Nl elma dieiere, 4>(e) wate Pe €19\ eee misieimiels aie + 0) erape Peel eierereieinisie “1m eel mini eee. H 18 8 laine meine tes al eleieleieieiaia(eie whole m\Simhstere S.91e) mej elelepetefaimie) ri. “ates Omi 1Fih (<1 elelaPe/ eth imis ie timrejaiateieieiieie bes evr ris + eheleimisi aera, HO Oh el Semin (= eh memie chet siateje/ apeiere:e\sieietepeie o/8e) Bl eterete eieheiere: rhevete niSie| Sia) elelejepat nieielmieieieteleimimiaiaie EF met) ia Lane | it o. ii ie ‘ wy rN) Aad My. ‘ 7 AL ol > i i A yi I ug | “4 i . Oh if * oN, Hh, oe he oie : pie Kea t ' ar) ¢ ee te y | 7 Wei fe \ wil Ni 1 sol 18 Deon i? A i i Vie ' j y : : ma 3 i cn 7" oF sh Nba Lv f if i t ' J { ~~ Ne ne a DEY, ry yi ¥ 7‘ oe i dA ig V4 : THE AMBRIDGE NATURAL HISTORY S. F. HARMER, Sc.D., F.R.S., Fellow of King’s College, Cambridge ; Keeper of the Department of Zoology in the British Museum (Natural History) AND Pee SHIP BY, M.A, Fellow and Tutor of Christs College, Cambridge ; Reader in Zoology in the University VOLUME IV 4 FEB 19 1987 LIBRARIES 75 ATHSON ARS. / MACMILLAN AND CO., LIMITED LONDON + BOMBAY + CALCUTTA MELBOURNE THE MACMILLAN COMPANY NEW YORK + BOSTON - CHICAGO ATLANTA - SAN FRANCISCO THE MACMILLAN CO. OF CANADA, LTD. TORONTO ansonian Ingti¢, is ON | SEP 20 1009 “N.4¥08 \ AS “onal Muse CRUSTACEA By Grorrrey Situ, M.A. (Oxon.), Fellow of New College, Oxford ; and the late W. F. R. WELpon, M.A. (D.Sc.,Oxon.), formerly Fellow of St. John’s College, Cambridge, and Linacre Professor of Human and Comparative Anatomy, Oxford MRILOBITES By Henry Woops, M.A., St. John’s College, Cambridge ; University Lecturer in Palaeozoology MITRODUCTION TO ARACHNIDA, AND KING-CRABS By A. E. Suiprey, M.A., F.R.S., Fellow and Tutor of Christ’s College, Cambridge ; Reader in Zoology EURYPTERIDA By Henry Woops, M.A., St. John’s College, Cambridge ; University Lecturer in Palaeozoology mem lONS, “SPIDERS, MITES? TICKS,. Erc: By Cecit Warsurton, M.A., Christ’s College, Cambridge ; Zoologist to the Royal Agricultural Society TARDIGRADA (WATER-BEARS) By A. E. Suiptey, M.A., F.R.S., Fellow and Tutor of Christ’s College, Cambridge ; Reader in Zoology PENTASTOMIDA By A. E. Surpiey, M.A., F.R.S., Fellow and Tutor of Christ’s College, Cambridge ; Reader in Zoology PYCNOGONIDA By D’Arcy W. Tuompson, C.B., M.A., Trinity College, Cambridge ; Professor of Natural History in University College, Dundee Rig AGVehiine AON UA NaC Or aie NEE ED Si MAREN’ S SRE ET -kON DON 1909 All the ingenious men, and all the scientific men, and all the fanciful men, in the world, with all the old German bogy- painters into the bargain, could never invent . . . anything so curious, and so ridiculous, as a lobster, CuHarLES KincsLey, The Water- Babies. For, Spider, thou art like the poet poor, Whom thou hast help’d in song. Both busily, our needful food to win, We work, as Nature taught, with ceaseless pains, Thy bowels thou dost spin, I spin my brains. SoutHry, To a Spider. Last o’er the field the Mite enormous swims, Swells his red heart, and writhes his giant limbs, Erasmus Darwin, The Temple of Nature. PREFACE Tue Editors feel that they owe an apology and some explanation to the readers of Zhe Cambridge Natural History tor the delay which has oceurred in the issue of this, the fourth in proper order, but the last to appear of the ten volumes which compose the work. The delay has been due principally to the untimely death of Professor W. F. R. Weldon, who had undertaken to write the Section on the Crustacea. The Chapter on the Branchiopoda is all he actually left ready for publication, but it gives an indication of the thorough way in which he had intended to treat his subject. He had, however, superintended the preparation of a number of beautiful illustrations, which show that he had determined to use, in the main, first-hand knowledge. Many of these figures have been incorporated in the article by Mr. Geoffrey Smith, to whom the Editors wish to express their thanks for taking up, almost at a moment’s notice, the task which had dropped from his teacher’s hand. A further apology is due to the other contributors to this volume. Their contributions have been in type for many years, and owing to the inevitable delays indicated above they have been called upon to make old articles new, ever an ungrateful labour. The appearance of this volume completes the work the Editors embarked on some sixteen years ago. It coincides with the cessation of an almost daily intercourse since the time when they “came up” to Cambridge as freshmen in 1880. S. F. HARMER. A. E. SHIPLEY. March 1909. 7 hy aa eek Fite te MS ys a ae ne at Oe ML WED ah dia ‘ + aA ; iyi? 4 ., d ~ iy baie, ‘ . é “i oa he . } i" ; & % + ‘ § ’ P . Pe AS ; Us ee » i! ’ in Ts Ch? a | Ve ' et : Cane ie ? P71 T true t,) IPAs vio» ‘ CONTENTS 2 PAGE SCHEME OF THE CLASSIFICATION ADOPTED IN THIS VOLUME . : : : xi CRUSTACEKA (GISLALIPMMIO as II CRUSTACEA JENERAL ORGANISATION ; ; : d , : ; f 3 3 CERAVRAMEY Ry elo CRUSTACEA (continued) ENTOMOSTRACA —- BRANCHIOPODA — PHYLLOPODA — CLADOCERA — WATER- KEEAS. .. 5 e . : : : 3 é : ; - . 18 CHEAPER Re Wl CRUSTACEA ENTOMOSTRACA (continued) CoPpEPODA ; , : : ; : 5 : 3 : : ; ; 5 COUSLAUEMDNO IR IV CRUSTACEA ENTOMOSTRACA (continued) 79 CIRRIPEDIA— PHENOMENA OF GROWTH AND SEX—OSTRACODA Vil vill CONTENTS (ONELAIE MID ay \W CRUSTACEA (continued) PAGE MALACOSTRACA: LEPTOSTRACA—PHYLLOCARIDA: HEUMALACOSTRACA: SYN- CARIDA — ANASPIDACEA: PERACARIDA — MysIpDAcEA — CuMACEA — IsopopA—AMPHIPODA : HOPLOCARIDA—STOMATOPODA . é ¢ Re CHAPTER VI CRUSTACEA MALACOSTRACA (continued) - EUMALACOSTRACA (CONTINUED): EUCARIDA — EUPHAUSIACEA — COMPOUND EyvES—DECAPODA . : ; . s ; ; ; . : papell: CECATP IDE Re Vib CRUSTACEA (continued) REMARKS ON THE DISTRIBUTION OF MARINE AND FRESH-WATER CRUSTACEA. 197 CHAPTER VIII CRUSTACEA (continued) TRILOBITA . : 5 g : é : , ; : : : = 42211 ARACHNIDA CHARADE Ry ake ARACHNIDA—INTRODUCTION . 255 (COMSLIN TE MND ay ON ARACHNIDA (continued) DELOBRANCHIATA = MEROSTOMATA—XIPHOSURA . ‘ ; : : ». 259 CHAPTER XI ARACHNIDA DELOBRANCHIATA (continued) EuRYPTERIDA=GIGANTOSTRACA . ‘ ; ‘ ‘ : : 5 5 teks CONTENTS ix CHAPTER XII ARACHNIDA (continued) PAGE EMBOLOBRANCHIATA—SCORPIONIDEA—PEDIPALPI . : A E é 52 PAE (OUSUAIP MNT R Ie DUUL ARACHNIDA EMBOLOBRANCHIATA (continued) ARANEAE—EXTERNAL STRUCTURE—INTERNAL STRUCTURE . , : 5 Sule CEPAGE TB Rae xcs ARACHNIDA EMBOLOBRANCHIATA (continued) ARANEAE (CONTINUED) — HaApirs — Ecpysis— TREATMENT OF YOUNG — MIGRATION — WeEsBs — Nests — Eac-cocoons — Poison — FERTILITY — ENEMIES—PROTECTIVE COLORATION—MIMICRY—SENSES—INTELLIGENCE —Matine Hapirs—Fossin SPIDERS . , : ; ; : 5 ephe (CHETAN IP INI IR O\Y ARACHNIDA EMBOLOBRANCHIATA (continued) ARANEAE (CONTINUED)—CLASSIFICATION : ; : 2 : : 5 Biel! CHEAP UNIB IR, EWA ARACHNIDA EMBOLOBRANCHIATA (continued) PALPIGRADI—SOLIFUGAE = SOLPUGAE—CHERNETIDEA = PSEUDOSCORPIONES . 422 (CIEUAAIE DIB IR, OSV IUL ARACHNIDA EMBOLOBRANCHIATA (continued) PopoGona = RICINULEI—PHALANGIDEA = OPILIONES—H ABITS—STRUCTURE— CLASSIFICATION f ; F 3 3 ; : : : ’ 4.3 9 CHABRLER XVEHI ARACHNIDA EMBOLOBRANCHIATA (continued) ACARINA— HARVEST-BUGS— Parasitic Mirrs—Ticks—SPpINNING MITEsS— STRUCTURE—METAMORPHOSIS—CLASSIFICATION : ; ; ». 454 x CONTENTS CHAPTER XIX ARACHNIDA (APPENDIX I) PAGE TARDIGRADA — OccURRENCE — EcpysIs — STRUCTURE DEVELOPMENT — AFFINITIES— BIOLOGY—DESICCATION—PARASITES—SYSTEMATIC . ee yi (C1ELAIP AIR, NOX ARACHNIDA (APPENDIX IT) PENTASTOMIDA — OccCURRENCE — Economic IMPORTANCE — STRUCTURE — DEVELOPMENT AND LIFE-HISTORY—SYSTEMATIC . : P ; . 488 PYCNOGONIDA CUEI/NIE MND RE, SOI PYCNOGONIDA : ; F : , . F 3 3 j 22 DOr INDEX 4 : : : - ; 3 : : : d 5 . 543 SCHEME OF THE CLASSIFIC IN THIS VOLUME The names of extinct groups are printed in italics. Divisions. Orders. Branchio- poda (p. 18) = Ye) = Copepoda =} (p. 55) Bo, a ° o =! Ay L (Continued on the next page. | CRUSTACEA (p. 3). ENTOMOSTRACA (p. 18). Sub-Orders. Tribes. Phyllopoda (pp. 19, 35) Ctenopoda { (p. 51) Caly ae e (pp. 38, Anomo- ease ee (p. 37) (p. 51) | Canes | i (pp. 38, 54) | ia Rita le (p. 57) rile eae (p. 57) ey ae (p. 58) | Peano i 61) x1 | | ATION ADOPTED Families. Branchipodidae (pp. 19, 35). A podidae (pp. 19, 36). Limnadidae (pp. 20, 36). Stitdaetp-ol). ae sdiidae (p. 51). aoe (p. 51). Bosminidae (p. 58). ee aphniidae (p. 53). Ly Paes = Chydoridae (p. 53). Pea ee (p. 54). Beas p. 54). Oat nil ae (p. 57). Centropagidae (p. 58). Candacidae (p. 60). Pontellidae (p. 60). Cyclopidae (pp. 61, 62). Harpacticidae (pp. 61, 62). Peltiidae (p. 63). Monstrillidae (p. 63). Ascidicolidae (p. 66). Asterocheridae (p. 67). Dichelestiidae (p. 68). xi SCHEME OF CLASSIFICATION Divisions. Orders. Sub-Orders, Tribes. Families. ( ( ( ( Oncaeidae (p. 69). Corycaeidae (p. 69). Lichomolgidae (p. 70). Ergasilidae (p. 71). Bomolochidae (pa): Chondracanthidae (p. 72). Eucopepoda’; Podoplea | Isokerandria 4 Philichthyidae Copepoda} (contd.) + (contd.) 1 (p. 69) (p. 73). (contd.) Nereicolidae (p. 73). Hersiliidae (p. 73). Caligidae (p. 73). Lernaeidae (p. 74). Lernaeopodidae (p27): Choniostomatidae L “(pi-76); | Argulidae (p. 76). ( ( Polyaspidae (p. 84). Pentaspidae (p. 87). Pedunculata. Thelphusidae = Potamon- idae (p. 191). Renee (p. 193). Oxyrhyncha Parthenopidae (p. 193). (p. 191) (ee (p. 193 \Carcinoplacidae (p. 195). Gonoplacidae (p. 195). Catometopa | Pinnotheridae (p. 195). (p. 193) Grapsidae (p. 196). | Gecarcinidae (p. 196). L ( Ocypodidae (p. 196). (Continued on the next page.) SCHEME OF CLASSIFICATION XV TRILOBITA (p. 221). Families. Agnostidae (p. 244). Shumardiidae (p. 245). Trinucleidae (p. 245). Harpedidae (p. 245). Paradoxidae (p. 246). Conocephalidae = Conocoryphidae (p. 247). Olenidae (p. 247). Calymenidae (p. 247). Asaphidae (p. 249). Bronteidae (p. 249). Phacopidae (p. 249). Cheiruridae (p. 250). Proétidae (p. 251). Enerinuridae (p. 251). Acidaspidae (p. 251). Lichadidue (p. 252). ARACHNIDA (p. 255). DELOBRANCHIATA=MEROSTOMATA (pp. 258, 259). Orders. Families. Sub-Families. f Xiphosurinae (p. 276). \ Tachypleinae (p. 276). Xiphosura (pp. 258, 259, 276) Eurypterida=Gigantostraca (pp. 258, 283) | Xiphosuridae (p. 276) \ ELurypteridue (p. 290). EMBOLOBRANCHIATA (pp. 258, 297). f Buthinae (p. 306). \ Centrurinae (p. 306). (faces (p. 307). Buthidae (p. 306) Urodacinae (p. 307). Scorpionidae (p. 306) Scorpioninae (p. 307). | Hemiscorpioninas (p. 307). Sunnis Ischnurinae (p. 307). (pp. 258, 297) Chaerilidae (p. 307). Megacorminae (p. 308). Chactidae (p. 307) « Euscorpiinae (p. 308). Chactinae (p. 308) Vejovidae (p. 308). . Bothriuridae (p. 308). Thelyphonidae (p. 312). Schizonotidae = Tartaridae ’ (p. 312). Tarantulidae = Phrynidae { (p. 312) | Liphistiidae (p. 386). Pedipalpi (pp. 258, 308 Tarantulinae (p. 313). Phrynichinae (p. 313). Charontinae (p. 313). ( Paratropidinae (p. 387). Actinopodinae (p. 387). : ve ; iginae (p. 387). ee ees 4 eee Al (p. Oe (1p Bie 3) Barychelinae (p. 389). | Aviculariinae (p. 389). \ Diplurinae (p. 390). Araneae (pp. 258, 314) (Continued on the next page.) XVI SCHEME OF CLASSIFICATION Orders. ( Araneae (contd.) 4 (Continued on the next page.) ee Families. Atypidae (p. 390). Vilistatidae (p. 391). Oecobiidae = Urocteidae (p. 392). Sicariidae =Scytodidae (p. 893). Hypochilidae (p. 393). Leptonetidae (p. 393). Oonopidae (p. 393). Hadrotarsidae (p. 394). Dysderidae (p. 394) Caponiidae (p. 395). Prodidomidae (p. 395). Drassidae (p. 396) Palpimanidae (p. 398). Eresidae (p. 398). Dictynidae (p. 398). Psechridae (p. 399). Zodariidae = Enyoidae (p. 399). Hersiliidae (p. 400). Pholeidae (p. 401). Theridiidae (p. 401) Epeiridae (p. 406) Uloboridae (p. 410) Archeidae (411). Mimetidae (p. 411). Thomisidae (p. 412) Zoropsidae (p. 415). Platoridae (p. 415). Agelenidae (p. 415) Sub-Families. { Dysderinae (p. 394). \ Segestriinae (p. 395). Wehr (p. 396). Clubioninae (p. 397). eae (p. 397). Micariinae (p. 397). ( Argyrodinae (p. 402). Episininae (p. 402). Theridioninae (p. 403). 4 Phoroncidiinae (p. 404). Erigoninae (p. 404). Formicinae (p. 405). ( Linyphiinae (p. 405). Theridiosomatinae (p. 407)- Tetragnathinae (p. 407). Argiopinae (p. 408). Nephilinae (p. 408). Epeirinae (p. 408). Gasteracanthinae (p. 409). Poltyinae (p. 410). Arcyinae (p. 410). Dinopinae (p. 410). Uloborinae (p. 410). Miagrammopinae (p. 411). ( Thomisinae = Misumeninae | (p. 412). Philodrominae (p. 413). 4 Sparassinae (p. 414). Aphantochilinae (p. 414). | Stephanopsinae (p. 414). (Selenopinae (p. 414). Cybaeinae (p. 415). Ageleninae (p. 416). Hahniinae (p. 416). Nicodaminae (p. 416). i XVil SCHEME OF CLASSIFICATION Orders. Sub-Orders. Families. ; - Pisauridae (p.416). | Lycosidae (p. 417). Ctenidae (p. 418). oe. . + Senoculidae (p. 418). Reantd. ) Oxyopidae (p. 419). Attidae =Salticidae (p. 419). Palpigradi (pp. 258, 422). ‘ Galeodidae (p. 428). Solifugae =Solpugae Solpugidae (p. 429) (pp. 258, 423) | ~ Hexisopodidae (p. 429). Chernetidea | =Chernetes = Pseudoscor- Cheliferidae (p. 436) piones (pp. 258, 430) Podogona PA Becaate® | i Bi (pp. 258, 439) i 1dae (p. ). ies } Sironidae (p. 448). Mecostethi | Phalangodidae (p. 448). . =Laniatores - Cosmetidae (p. 449). eaanicics j (p. 448) | Gonyleptidae (p. 449). pp. 258, 440) 3 5 | Phalangiidae (p. 449) PI Plagiostethi | = I =Palpatores { Ischyropsalidae (p. 451). (p. 449) | Nem ep tid ; 451) p. 449 emastomatidae (p. 451). ( Trogulidae (p. 452). c : 3 Eriophyidae aS ie i = Phytoptidae (p.464). Ie | Demodicidae (p. 465). eee \ Sarcoptidae (p. 466) (p. 465) ri Oribatidae (p. 467). . ‘aS | Argasidae (p.469). Metastigmata 1g. “Ixodidae (p. 469). (p. 467) oe | Acarina ame = Acari J Gamasidae (p. 470) = Acaridea . (pp. 258, 454) Zena Tarsonemidae (p. 471). ( Bdellidae (p. 471). Halacaridae (p. 472). Hydrachnidae (p. 472). Prostigmata | (p. 471) } | Trombidiidae (p. 472) ; L (hue eas } Opitioacaridte (p. 473). Sub-Families. ( Rhagodinae (p. 429). Solpuginae (p. 429). + Daesiinae (p. 429). Eremobatinae (p. 429). Karshiinae (p. 429). | Cheliferinae (p. 436). , Garypinae (pp. 436, 437). | Obisiinae (pp. 436, 437). f Sclerosomatinae (p. 449). \ Phalangiinae (p. 450). ( Sarcoptinae (p. 466). Analgesinae (p. 466). | Tyroglyphinae (p. 466). { Gamasinae (p. 470). \ Dermanyssinae (p. 471). r Limnocharinae (p. 472). Caeculinae (p. 472). Tetranychinae (p. 472). Cheyletinae (p. 473). Erythraeinae (p. 473). _ Trombidiinae (p. 473). XVlll SCHEME OF CLASSIFICATION Orders. TARDIGRADA (pp. 258, 477). PENTASTOMIDA (pp. 258, 488). PYCNOGONIDA = PODOSOMATA = PANTOPODA (p. 501). Families. Decolopodidae (p. 531). Colossendeidae = Pasithoidae (p. 532). Eurycididae = Ascorhynchidae (p. 533). Ammotheidae (p. 534). Rhynchothoracidae (p. 535) Nymphonidae (p. 536). Pallenidae (p. 537). Phoxichilididae (p. 538). Phoxichilidae (p. 539). Pycnogonidae (p. 539). CRUSTACEA. CHAPTERS I awn III-VII BY GEOFFREY SMITH, M.A. (Oxon.) Fellow of New College, Oxford © CHAPTER II BY THe Late W. F. R. WELDON, M.A. (D.Sc. Oxon.) emery Fellow of St. John’s College, Cambridge, and Linacre Professor of Human and Comparative Anatomy, Oxford ay CHAPTER I CRUSTACEA GENERAL ORGANISATION THE Crustacea are almost exclusively aquatic animals, and they play a part in the waters of the world closely parallel to that which insects play on land. The majority are free-living, and gain their sustenance either as vegetable-feeders or by preying upon other animals, but a great number are scavengers, picking clean the carcasses and refuse that litter the ocean, just as maggots and other insects rid the land of its dead cumber. Similar to insects also is the great abundarfce of individuals which represent many of the species, especially in the colder seas, and the naturalist in the Arctic or Antarctic oceans has learnt to hang the carcasses of bears and seals over the side of the boat for a few days in order to have them picked absolutely clean by shoals of small Amphipods. It is said that these creatures, when crowded sufficiently, will even attack living fishes, and by sheer press of numbers impede their escape and devour them alive. Equally surprising are the shoals of minute Copepods which may discolour the ocean for many miles, an appearance well known to fishermen, who take profitable toll of the fishes that follow in their wake. Despite this massing together we look in vain for any elaborate social economy, or for the development of complex instincts among Crustacea, such as excite our admiration in many insects, and though many a crab or lobster is sufficiently uncanny in appearance to suggest unearthly wisdom, he keeps his intelligence rigidly to himself, encased in the impenetrable reserve of his armour and vindicated by the most powerful, of pincers. It is chiefly in the variety of structure and in the multifarious phases of life-history that 2 2] A CRUSTACEA CHAP. the interest of the Crustacea lies. Before entering into an examination of these matters, it will be well to take a general survey of Crustacean organisation, to consider the plan on which these animals are built, and the probable relation of this plan to others met with in the animal kingdom. The Crustacea, to begin with, are a Class of the enormous Phylum Arthropoda, animals with metamerically segmented bodies and usually with externally jointed limbs. Their bodies are thus composed of a series of repeated segments, which are on the whole similar to one another, though particular segments may be differentiated in various respects for the performance of different functions. This segmentation is apparent externally, the surface of a Crustacean being divided typically into a number of hard chitinous rings, some of which may be fused rigidly together, as in the carapace of the crabs, or else articulated loosely. Each segment bears typically a pair of jointed limbs, and though they vary greatly in accordance with the special functions for which they are employed, and may even be absent from certain segments, they may yet be reduced to a common plan and were, no doubt, originally present on all the segments. Passing from the exterior to the interior of the body we find, generally speaking, that the chief system of organs which exhibits a similar repetition, or metameric segmentation, is the nervous system. This system is composed ideally of a nervous ganglion situated in each segment and giving off peripheral nerves, the several ganglia being connected together by a longitudinal cord. This ideal arrangement, though apparent during the embryonic development, becomes obscured: to some extent in the adult owing to the concentration or fusion of ganglia in various parts of the body. The other internal organs do not show any clear signs of segmentation, either in the embryo or in the adult ; the alimentary canal and its various diverticula lie in an unsegmented body-cavity, and are bathed in the blood which courses through a system of narrow canals and irregular spaces which surround all the organs of the body. A single pair, or ut most two pairs of kidneys are present. 3 The type of segmentation exhibited by the Crustacea is thus of a limited character, concerning merely the external skin with its appendages, and the nervous system, and not touching any i SEGMENTATION 5 of the other internal organs.’ In this respect the Crustacea agree with all the other Arthropods, in the adults of which the segmentation is confined to the exterior and to the nervous system, and does not extend to the body-cavity and its contained organs; and for the same reason they differ essentially from all other metamerically segmented animals, e.g. Annelids, in which the segmentation not only affects the exterior and the nervous system, but especially apples to the body-cavity, the musculature, the renal, and often the generative organs. The Crustacea also resemble the other Arthropoda in the fact that the body-cavity contains blood, and is therefore a “ haemocoel,’ while in the Annelids and Vertebrates the segmented body-cavity is distinct from the vascular system, and constitutes a true “coelom.” To this important distinction, and to its especial application to the Crustacea, we will return, but first we may consider more narrowly the segmentation of the Crustacea and its main types of variation within the group. In order to determine the number of segments which compose any particular Crustacean we have clearly two criteria: first, the rings or somites of which the body is composed, and to each of which a_ pair of limbs must be originally ascribed; and, second, the nervous ganglia. - Around and behind the region of the mouth there is very little difficulty in determining the segments of the body, if we allow embryology to assist anatomy, but in front of the mouth the matter is not so easy. In the Crustacea the moot point is whether we consider the paired eyes and first pair of antennae as true appendages. belong- ing to two true segments, or whether they are structures sui generis, not homologous to the other hmbs. With regard to the first antennae we are probably safe in assigning them to a true body-segment, since in some of the Entomostraca, eg. Apus, the nerves which supply them spring, not from the brain as in more highly specialised forms, but from the commissures which pass round the oesophagus to connect the dorsally lying brain to the ventral nerve-cord. The paired eyes are always inner- vated from the brain, but the brain, or at least part of it, 1s very 1 The muscles are to a certain extent segmented in correspondence with the limbs ; and the heart, in Phyllopeda and Stomatopoda, may have segmentally arranged ostia. 6 CRUSTACEA CHAP. probably formed of paired trunk-ganglia which have fused into a common cerebral mass ; and the fact that under certain cireum- stances the stalked eye of Decapods when excised with its peripheral ganglion’ can regenerate in the form of an antenna, is perhaps evidence that the lateral eyes are borne on what were once a pair of true appendages. Now, with regard to the segmentation of the body, the Crustacea fall into three categories: the Entomostraca, in which the number of segments is indefinite; the Malacostraca, in which we may count nineteen segments, exclusive of the terminal piece or telson and omitting the lateral eyes; and the Leptostraca, including the single recent genus Nebalia, in which the segmen- tation of head and thorax agrees exactly with that of the Malacostraca, but in the abdomen there are two additional segments. It has been usually held that the indefinite number of segments characteristic of the Entomostraca, and especially the indefinitely large number of segments characteristic of such Phyllopods as Apus, preserves the ancestral condition from which the definite number found in the Malacostraca has been derived ; but recently it has been clearly pointed out by Professor Carpenter” that the number of segments found in the Malacostraca and Leptostraca corresponds with extraordinary exactitude to the number determined as typical in all the other orders of Arthropoda. This remarkable correspondence (it can hardly be coincidence) seems to point to a common Arthropodan plan of segmentation, lying at the very root of the phyletic tree, and if this is so, we are forced to the conclusion that the Malacostraca have retained the primitive type of segmentation in far greater perfection than the Entomostraca, in some of which many segments have been added, e.g. Phyllopoda, while in others segments have been suppressed, e.g. Cladocera, Ostracoda. It may be objected to this view of the primitive condition of segmentation in the Crustacea that the Trilobites, which for various reasons are regarded as related to the ancestral Crustaceans, exhibit an indefinite and often very high number of segments; but, as Professor Carpenter has pointed out, the oldest and most primitive of Trilobites, such as Olenellus, possessed 1 Herbst, Arch. Entwick. Mech. ii., 1905, p. 544. 2 Quart. J. Micr. Sci. xlix., 1906, p. 469. f. p. 263), 2 ) OF ARTHROPODS SEGMENTATION The following table shows the segmentation of the body in the Malacostraca, as compared with that of Limulus (¢ It will be seen that the correspondence, though not exact, is very close, especially in the first four columns, the number of segments in Peripatus being very variable in the different Insecta, the primitive Myriapod Scolopendrella, and Peripatus. species. few segments which increase as we pass from Cambrian to Carboniferous genera. ‘quosead eq Avi sesvpuedde Arozepnque 1g sv AuvUl sy z “DLMQAN UL YUOSeIg 7 vpodeiiA wos[ay, | COSENF uos[aL, UOs[aT, WOS|aT, eee | spodoo.aag PE a sce “WPL | S(ULIT poonpey WA it ig ie 199 “UIST | mae ‘ U6 = “ug | “WIGL “USI | a vets * ee EG UC les! “WOOL iim el ~ iy 8S “TOL “ 146 . yg ss saBepuodde on te. 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In a typical Crustacean, besides the paired eyes, which may be borne on stalks, possibly homologous to highly modified limbs, there are present, first, two pairs of rod-like or filamentous antennae, which in the adult are usually specialised for sensory purposes, but frequently retain their primitive function as locomotory limbs even in the adult, e.g. Ostracoda; while in the Nauplius larva, found in almost all the chief subdivisions of the Crustacea, the two pairs of antennae invariably aid in locomotion, and the base of the second antennae is usually furnished with sharp biting spines which assist mastication. Following the antennae is a pair of mandibles which are fashioned for biting the food or for piercing the prey, and posterior to these are two pairs of maxillae, biting organs more slightly built than the mandibles, whose function it is to lacerate the food and prepare it for the more drastic action of the mandibles. So far, with comparatively few exceptions, the order of specialisation is invariable; but behind the maxillae the trunk-appendages vary greatly both in structure and function in the different groups. As a general rule, the first or first few thoracic limbs are turned forwards toward the mouth, and are subsidiary to mastication; they are then called maxillipedes; this happens usually in the Malacostraca, but to a much less extent in the Entomostraca; and in any case these appendages immediately behind the maxillae never depart to any great extent from a limb-hke structure, and they may graduate insensibly into the ordinary trunk-appendages. The latter show great diversity in the different Crustacean groups, according as the animals lead a natatory, creeping, or parasitic method of life; they may be foliaceous, as in the Branchiopoda, or biramous, as in the swimming thoracic and abdominal appendages of the Mysidae, or simply uniramous, as in the walking legs of the higher Decapoda, and the clinging legs of various parasitic forms. Without going into detailed deviations of structure, many of which will be described under the headings of special groups, it is clear from the foregoing description and from Fig. 1 (p. 10), that three main types of appendage can be distinguished: first, the foliaceous or multiramous; second, the biramous; and, third, the wniramous. I APPENDAGES 9 We may dismiss the uniramous type with a few words: it is obviously secondarily derived from the biramous type; this can be proved in detail in nearly every case. Thus, the uniramous second antennae of some adult forms are during the Nauplius stage invariably biramous, a condition which is retained in the adult Cladocera. Similarly the uniramous walking legs of many Decapoda pass through a biramous stage during development, the outer branches or exopodites of the limbs being suppressed subsequently, while the primitively biramous condition of the thoracic limbs is retained in the adults of the Schizopoda, which doubtless own a common ancestry with the Decapoda. The only Crustacean limb which appears to be constantly uniramous both in larval and adult hfe is the first pair of antennae. We are reduced, therefore, to two types—the foliaceous and biramous. Sir E. Ray Lankester,’ in one of his most incisive morphological essays, has explained how these two types are really fundamentally the same. He compares, for instance, the foliaceous first maxillipede (Fig. 1, A), or the second maxilla (Fig. 1, B) of a Decapod, e.g. Astacus, with the foliaceous thoracic linb of Branchipus (Fig. 1, D), and with the typically biramous first maxillipede of a Schizopod (Fig. 1, F). In each case there is present, on the outer edge of the limb, one or more projections or epipodites which are generally specialised for respiratory purposes, and may carry the gills. The 6th and 5th “endites” in the foliaceous limb (Fig. 1, D) are compared with the exopodite and endopodite respectively of the biramous limb, while the endites 4-1 of the foliaceous lmb are found in the basal joints of the biramous limb. Lankester presumes that the biramous type of limb throughout has been derived from the foliaceous type by the suppression of the endites 1-4, as discrete rami, and the exaggerated development of the endites 5 and 6, as above indicated. The essential fact that the two types of limb are built on the same plan may be considered as established; but it may be urged that the biramous type represents this common plan more nearly than the foliaceous. It is, at any rate, certain that -in the maxillipedes of the Decapoda we witness the conversion of the biramous type into the foliaceous by the expansion of the basal joints concomitantly with the assumption by the 1 Quart. J. Micr. Sci. xxi., 1881, p. 343. IO CRUSTACEA CHAP. maxillipedes of masticatory functions. Thus in the Decapoda the first maxillipede is decidedly foliaceous owing to the expanded Fic. 1.—Appendages of Crustacea (A-G) and Trilobita (H). A, First maxillipede of Astacus; B, second maxilla of Astacus; ©, second walking-leg of Astacus ; D, thoracie limb of Branchipus ; E, first maxillipede of Mysis ; F, first maxillipede of Gnathophausia ; G@, thoracic limb of Nebalia ; H, thoracic limb of Triarthrus. bp, Basipodite; br, bract; cp, carpopodite ; cxp, coxopodite ; ca.s, coxopoditic setae ; dp, dactylopodite ; end, endopodite ; ep, epipodite ; ex, exopodite ; 7p, ischiopodite ; mp, meropodite ; pp, propodite ; 1-6, the six endites. “onathobases” (Fig. 1, A, bp, cap), and the second maxilli- pedes are flattened, with their basal joints somewhat expanded and furnished with biting hairs; but in the “ Schizopoda” I BODY-CAVITY II (e.g. Mysis) the first maxillipede is a typical biramous limb, though the expanded gnathobases in some forms are beginning to project (Fig. 1, EK), while the limb following, which corresponds to the second maxillipede of Decapods, is simply a biramous swimming leg. Besides this obvious conversion of a biramous into a foliaceous limb, further evidence of the fundamental ‘character of the biramous type is found, first, in its invariable occurrence in the Nauplius stage, which does not necessarily mean that the ancestors of the Crustacea possessed this type ‘of limb in the adult, but which does imply that this type of limb was possessed at some period of life by the common » ancestral Crustacean ; and, second, the limbs of the Trilobita, a group which probably stands near the origin of the Crustacea, have been shown by Beecher to conform to the biramous type (Fig. 1, H). Furthermore, the thoracic limbs of Nebalia, an animal which combines many of the characteristics of Entomostraca and Malacostraca, and is therefore considered as a primitive type, despite their flattened character, are really built upon a biramous plan (Fig. 1, G). In conclusion, we may point out that this view of the Crustacean limb, as essentially a biramous structure, agrees with the conclusion derived from our consideration of the segmenta- tion of the body, and points less to the Branchiopoda as primitive Crustacea and more to some generalised Malacostracan type. So far we have shortly dealt with those systems of organs which are clearly affected by the metameric seementation of the body: we must now expose the condition of the body-cavity to a similar scrutiny. If we remove the external integument of a Crustacean, we find that the internal organs do not lie in a ‘spacious and discrete body-cavity, as is the case in the Annelids and Vertebrates, but that they are packed together in an irregular system of spaces (“haemocoel”) in communication with the vascular system and containing blood. In the Entomostraca and smaller forms generally, a definite vascular system hardly exists, ~ though a central heart and artery may serve to propel the blood through the irregular lacunae of the body-cavity; but in the larger Malacostraca a complicated system of arteries may be present which pour the blood into fairly definitely arranged Spaces surrounding the chief organs. These spaces return the TZ CRUSTACEA CHAP. blood to the pericardium, and so to the heart again through the apertures or ostia which pierce its walls. This condition of the body-cavity or haemocoel is reproduced in the adults of all Arthropods, but in some of them by following the development we can trace the steps by which the true coelom is replaced by the haemocoel. In the embryos of all Arthropods except the Crustacea, a true closed metamerically segmented coelom is formed as a split in the mesodermal embryonic layer of cells, distinct from the vascular system. During the course of development the segmented coelomic spaces and their walls give rise to the reproductive organs and to certain renal organs in Peripatus, Myriapoda, and Arachnida (nephridia and coxal glands), but the general body-cavity 1s formed as an extension of the vascular system, which is laid down outside the coelom by a canaliculisation of the extra-coelomic mesoderm. In the embryos of the Crustacea, however, there is never at any time a closed segmented coelom, and in this respect the Crustacea differ from all other Arthropods. The only clear instance in which metamerically repeated mesodermal cavities have been seen in the embryo Crustacean is. that of Astacus; here Reichen- bach? states that in the abdomen segmental cavities are formed which subsequently break down; but even in this instance no connexion has been shown to subsist between these embryonic cavities and the reproductive and excretory organs of the adult. Since the connexion between the coelom and the excretory organs is always a very close one throughout the animal kingdom, interest naturally centres upon the renal organs in Crustacea, and it has been suggested that these organs in Crustacea represent the sole remains, with the possible exception of the gonads, of the coelom. Since, at any rate, a part of the kidneys appears to be developed as a closed sac in the mesoderm, and since they possess a possible segmental value, this suggestion is plausible; but, on the other hand, since there are never more than two pairs of kidneys, and since they are totally unconnected with the gonads or with any other indication of a segmented coelom, the suggestion remains purely hypothetical. The renal organs of the Crustacea, excluding the Malpighian tubes present in some Amphipods which open into the alimentary canal, and resemble the Malpighian tubes of Insects, consist of 2 Abhandl. Senckenberg. Nat. Gesellsch. xiv., 1886. I : KIDNEYS Tes two pairs—the antennary gland, opening at the base of the second antenna, and the maxillary gland, opening on the second maxilla. These two pairs of glands rarely subsist together in the adult condition, though this is said to be the case in Nebalia and possibly J/ysis; the antennary glands are characteristic of adult Malacostraca' and the larvae of the Entomostraca, while the maxillary glands (“shell-glands”) are present in adult Entomo- straca and larval Malacostraca, that is to say, the one pair replaces the other in the two great subdivisions of the Crustacea. The shell- gland of the Entomostraca is a simple structure consisting of a coiled tube opening to the exterior on the external branch of the second maxilla, and ending blindly in a dilated vesicle, the end- sac. The antennary glaud of the Malacostraca is usually more complicated: these complications have been studied especially by Weldon,” Allen, and Marchal* in the Decapoda. In a number of forms we have a tube opening to the exterior at the base of the second antenna, and expanding within to form a spacious bladder into which the coiled tubular part of the kidney opens, while at the extremity of this coiled portion is the vesicle called the end-sac. This arrangement may be modified; thus in Palaemon Weldon described the two glands as fusing together above and below the oesophagus, the dorsal commissure expand- ing into a huge sac stretching dorsally down the length of the body. This closed sac with excretory functions thus comes to resemble a coelomic cavity, and the view that it is really coelomic has indeed been upheld. A modified form of this view is that of Vejdovsky, who describes a funnel-apparatus leading from the coiled tube into the end-sac of the antennary gland of Amphipods; he regards the end-sac alone as representing the coelom, while the funnel and coiled tube represent the kidney opening into it. Not very much is known of the development of these various structures. Some authors have considered that both antennary and maxillary glands are developed in the embryo from ecto- dermal inpushings, but the more recent observations of Waite * on Homarus americanus indicate that the antennary gland at ' The Cumacea, Anaspidacea, and certain Isopods possess a maxillary gland only. 2 Quart. J. Micr. Sci. xxxii., 1891, p. 279. ® Arch. Zool. Exp. (2) x., 1892, p. 57. * Bull. Mus. Comp. Zool. Harvard, xxxv., 1899, p. 152. 14 CRUSTACEA _ CHAP- any rate is a composite structure, formed by an ectodermal ingrowth which meets a mesodermal strand, and from the latter are produced the end-sac and perhaps the tubular excretory portions of the gland with their derivatives. With regard to the possible metameric repetition of the renal organs, it is of interest to note that by feeding dJ/ysis and Nebalia on carmine, excretory glands of a simple character were observed by Metschnikoff situated at the bases of the thoracic limbs. The alimentary canal of the Crustacea is a straight tube composed of three parts—a mid-gut derived from the endoderm of the embryo, and a fore- and hind-gut formed by ectodermal invaginations in the embryo which push into and fuse with the endodermal canal. The regions of the fore- and hind-gut can be recognised in the adult by the fact of their bemg lined with the chitinous investment which is continued over the external surface of the body forming the hard exoskeleton, while the mid-gut is naked. The chitinous lining of fore- and hind-gut is shed whenever the animal moults. In the Malacostraca, in which a complicated “ gastric mill” may be present, the chitinous lining of this part of the gut is thrown into ridges bearing teeth, and this stomach in the crabs and lobsters reaches a high degree of complication and materially assists the mastication of the food. The gut is furnished with a number of secretory and metabolic glands ; the so-called liver, which is probably a hepato- pancreas, opening into the anterior end of the mid-gut, is directed forwards in most Entomostraca and backwards in the Malacostraca, in the Decapoda developing into a complicated branching organ which fills a large part of the thorax. In the Decapoda peculiar vermiform caeca of doubtful function are present, a pair of which — open into the gut anteriorly where fore- passes into mid-gut, and a single asymmetrically placed caecum opens posteriorly into the alimentary tract where mid- passes into hind-gut. The disposition of these caeca, marking as they do the morphological position of fore-, mid-, and hind-gut, is of peculiar interest owing to the variations exhibited. From some un- published drawings of Mr. E. H. Schuster, which he kindly lent me, it appears that in certain Decapods, eg. Callianassa sub- terranea, the length of the mid-gut between the anterior and posterior caeca is very long; in Carcinus maenas it is consider- I REPRODUCTIVE ORGANS 15 able; in Maia squinado it is greatly reduced, the caeca being closely approximated; while in Galathea strigosa the caeca are greatly reduced, and the mid-gut as a separate entity has almost disappeared. The relation of these variations to the habits of the different crabs and to their modes of development is un- known. The reproductive organs usually make their appearance as a small paired group of mesodermal cells in the thorax compara- tively late in hfe; and neither in their early development nor in the adult condition do they show any clear signs of segmenta- tion or any connexion with a coelomic cavity. The sexes are usually separate, but hermaphroditism occurs sporadically in many forms, and as a normal condition in some parasitic groups (see pp. 105-107). The adult gonads are generally simple paired tubes, from the walls of which the germ-cells are produced, and as these grow and come to maturity they fill up the cavities of the tubes; special nutrient cells are rarely differentiated, though in some cases (e.g. Cladocera) a few ova nourish themselves by devouring their sister-cells (see p. 44). The oviducts and vasa deferentia are formed as simple outgrowths from the gonadial tubes, which acquire an opening to the exterior ; they are usually poorly supplied with accessory glands, the epithelium of the canals often supplying albuminous secretions for cementing the egos together, while the lining of the vasa deferentia may be instrumental in the formation of spermatophores for transferring large packets of spermatozoa to the female. In the vast majority of Crustacea copulation takes place, the male passing spermatophores or free spermatozoa into special receptacles (spermathecae), or into the oviducts of the female. The sperma- tophores are hollow chitinous structures in which the sperma- tozoa are packed; they are often very large and assume charac- teristic shapes, especially in the Decapoda. The spermatozoa show a great variety of structure, but they conform to two chief types—the filiform, which are provided with a long whip-like flagellum; and the amoeboid, which are furnished with radiating pseudopodia, and are much slower in their movements. The amoeboid spermatozoa of some of the Decapoda contain in the cell-body a peculiar chitinous capsule, and Koltzofft has observed that when the spermatozoon has 1 Arch. f. mikr. Anat. \xvii., 1906, p. 364. 16 . CRUSTACEA CHAP. settled upon the surface of the egg the chitinous capsule becomes suddenly exceedingly hygroscopic, swells up, and explodes, driving the head of the spermatozoon into the egg. We cannot enter here into a description of the embryological changes by which the egg is converted into the adult form. Crustacean eges as a whole contain a large quantity of yolk, but in some forms total segmentation occurs in the early stages, which is converted later into the pyramidal type, ae. the blastomeres are arranged round the edge, and the yolk in the centre is only partly segmented to correspond with them. The eggs during the early stages of development are in almost all cases (except Branchiura, p. 77, and Anaspides, p. 116) carried about by the female either in a brood-pouch (Branchiopoda, Ostracoda, Cirripedia, Phyllocarida, Peracarida), or agglutinated to the hind legs or some other part of the body (Copepoda, Eucarida), or in a chamber formed from the maxillipedes (Stomatopoda). Development may be direct, without a complicated metamorphosis, or indirect, the larva hatching out in a form totally different to the adult state, and attaining the latter by a series of transformations and moults. The various larval forms will be described under the headings of the several orders. The respiratory organs are typically branchiae, ze. branched filamentous or foliaceous processes of the body- surface through which the blood circulates, and is brought into close relation with the oxygen dissolved in the water. In most of the smaller Entomostraca no special branchiae are ‘present, the interchange of gases taking place over the whole body-surface; but in the Malacostraca the gills may reach a high degree of specialisation. They are usually attached to the bases of the thoracic hmbs (“ podobranchiae ”), to the body- wall at the bases of these limbs, often in two series (“arthro- branchiae ”), and to the body-wall some way above the limb- articulations (“pleurobranchiae”). In an ideal scheme each thoracic appendage beginning with the first maxillipede would possess a podobranch, two arthrobranchs, and a pleurobranch, but the full complement of gills is never present, various members of the series being suppressed in the various orders, and thus giving rise to “branchial formulae” typical of the different groups. After this brief survey of Crustacean organisation we I THE ARTHROPODS A NATURAL GROUP I may be able to form an opinion upon the position of the Crustacea relative to other Arthropoda, and upon the question debated some time ago in the pages of Natural Science’ whether the Arthropoda constitute a natural group. The Crustacea plainly agree with all the other Arthropoda in the possession of a rigid exoskeleton segmented into a number of somites, in the possession of jointed appendages metamerically repeated, some of which are modified to act as jaws; they further agree in the general correspondence of the number of segments of which the body is primitively composed; the condition of the body- cavity or haemocoel is also similar in the adult state. An apparently fundamental difference is found in_ the entire absence during development of a segmented coelom, but since this organ breaks down and is much reduced in all adult Arthropods, it is not difficult to beheve that its actual formation in the embryo as a distinct structure might have been secondarily suppressed in Crustacea. The method of breathing by gills is paralleled by the respiratory structures found in Limulus and Scorpions; the transition, if it occurred, from branchiae to tracheae cannot, it is true, be traced, but the separation of Arthropods into phyletically distinct groups of Tracheata and Branchiata on this single characteristic is inadmissible. On the whole the Crustacea may be considered as Arthropods whose progenitors are to be sought for among the Trilobita, from whose near relations also probably sprang Limulus and the Arachnids. PViol.e Boi pp. o/s 264. VOL. IV C CHAPTER, a CRUSTACEA (CONTINUED) : ENTOMOSTRACA——BRANCHIOPODA— PHY LLOPODA——CLADOCERA——WATER-FLEAS SUB-CLASS I.—ENTOMOSTRACA. THE Entomostraca are mostly small Crustacea in which the seginentation of the body behind the head is very variable, both in regard to the number of segments and the kind of differentia- tion exhibited by those segments and their appendages. An unpaired simple eye, known as the Nauplius eye from its universal presence in that larval form, often persists in the adult, and though lateral compound eyes may be present they are rarely borne on movable stalks. In the adult the excretory gland (“shell-gland”) opens on the second maxillary segment, but in the larval state or early stages of development a second antennary gland may also be present, which disappears in the adult. The liver usually points forwards, and is simple and saccular in structure, and the stomach is not complicated by the formation of a gastric mill. With the exception of most Clado- cera and Ostracoda the young hatch out in the Nauplius state. Order I. Branchiopoda.' The Branchiopods are of small or moderate size, with flattened and lobate post-cephalic limbs, and with functional gnathobases. Median and lateral eyes are nearly always present. The labrum is large, and the second maxillae are small or absent in the adult. Branchiopods are found in every part of the world; a few are marine, but the great majority are confined to inland lakes and ponds, or to slowly-moving streams. The fresh waters, from the ' For this use of the term Branchiopoda, ef. Boas, Morph. Jahrb. viii., 1883, p. 519. 18 CHAP. II ENTOMOSTRACA—BRANCHIOPODA 19 smallest pools to the largest lakes, often swarm with them, as do those streams which flow so slowly that the creatures can obtain oceasional shelter among vegetation along the sides and bottom without being swept away, while even rivers of considerable swift- ness contain some Cladocera. Several Branchiopods are found in the brackish waters of estuaries, and some occur in lakes and pools so salt that no other Crustacea, and few other animals of any kind, can live in them. The great majority swim about with the back downwards, collecting food in the ventral groove between their post-oral limbs, and driving it forwards, towards the mouth, by movements of the gnathobases (p. 10). The food collected in this way consists largely of suspended organic mud, together with Diatoms and other Algae, and Infusoria; the larger kinds, however, are capable of gnawing objects of considerable size, Apus being said to nibble the softer insect larvae, and even tadpoles. Many Cladocera (e.g. Daphnia, Simocephalus) may be seen to sink to the bottom of an aquarium, with the ventral surface down- wards, and to collect mud, or even to devour the dead bodies of their fellows, while Leptodora is said to feed upon living Copepods, which it catches by means of its antennae. The Branchiopoda fall naturally into two Sub-orders, the PHYLLOPODA including a series of long-bodied forms, with at least ten pairs of post-cephalic limbs, and the CLADOCERA with shorter bodies and not more than six pairs of post-cephalic hmbs. Sub-Order 1. Phyllopoda. The Phyllopoda include a series of genera which differ greatly in appearance, owing to differences in the development of the carapace, which are curiously correlated with differences in the position of the eyes. Except in these points, the three families which the sub-order contains are so much alike that they may conveniently be described together. In the BRANCHIPODIDAE the carapace is practically absent, being represented only by the slight backward projection on each side of the head which contains the kidney (Fig. 2); the paired eyes are supported on mobile stalks, and project freely, one on either side of the head. In the AropmpAx! the head is broad and depressed, the ventral 1 Bernard, ‘‘ The Apodidae,” Nature Series, 1892. 20 CRUSTACEA—-BRANCHIOPODA CHAP. side being nearly flat, the dorsal stirface convex; the hinder margin of the head is indicated dorsally by a transverse cervical ridge, bounded by two grooves, behind which the carapace projects backwards as a great shield, covering at least half the body, but attached only to the back of the head. In Lepidurus productus the head and carapace together form an oval expansion, deeply emarginate at the hinder, narrower end, the sides of the emargination being toothed. The carapace has a strong median keel. The kidneys project into the space between the folds of skin which form the carapace, and their coils can be seen on each side, the terminal part of each kidney-tube enter- ing the head to open at the base of the second maxilla. In ali ES Fia. 2.—Chirocephalus diaphanus, female, x 5, Sussex. D.O, Dorsal organ ; /, heart ; Ov, ovary; U, uterus; V, external generative opening. Branchiopoda with a well-developed carapace the kidney is enclosed in it in this way, whence the older anatomists speak of it as the “ shell-gland.” Associated with the development of the carapace, in this and in the next family, is a remarkable condition of the lateral eyes, which are sessile on the dorsal surface of the head, and near the middle line, the median eye being slightly in front of them. During embryonie life a fold of skin grows over all three eyes, so that a chamber is formed over them, which communicates with the exterior by a small pore in front. In the LimnapipaE the body is laterally compressed, and the carapace is so large that at least the post-cephalic part of the body,.and generally the head also, can be enclosed within it. In Limnetis (Fig. 3) the dorsal surface of the head is bent downwards and is much compressed, the carapace being attached Il STRUCTURE OF LIMNADIIDAE 21 to it only for a short distance near the dorsal middle line. The sides of the carapace are bent downwards, and their margins can be pulled together by a transverse adductor muscle, so that the whole structure forms an ovoid or spheroidal case, from which the head projects in front, while the rest of the body is entirely contained within it. When the adductor muscle is relaxed the edges of the carapace gape slightly, like the valves of a Lamellibranch shell, and food- particles are drawn through the opening thus formed into the ventral groove by the movements : Fig. 3.—Limnetis brachyura, x 15. of the thoracic feet, loco- (After G. 0. Sars.) motion being chiefly effected by the rowing action of the second antennae, as in the Cladocera, to which all the Limnadiidae present strong resemblances in their method of locomotion, in the condition of the carapace, and in the form of the telson. In Limnadia and Estheria the carapace projects not only backwards from the point of attachment to the head, but also forwards, so that the head can be enclosed by it, together with the rest of the body. In all these genera the carapace is flexible along the middle dorsal line; in Hstheria especially the softening of the dorsal cuticle goes so far that a definite hinge-line is formed, and this, together with the deposition of the lateral cuticle in lines con- centrically arranged round a projecting umbo, gives the carapace a strong superficial likeness to a Lamellibranch shell, for which it is said to be frequently mistaken by collectors. The eyes of the Limnadiidae are enclosed in a chamber formed by a growth of skin over them, as in Apodidae, but the pore by which this chamber communicates with the exterior is even more minute than in Apus. The paired eyes are so close together that they may touch (Limnadia, Estheria) or fuse (Limnetis); they are farther back than in the Apodidae, while the ventral curvature of the head causes the median eye to lie below them. In all i) i) CRUSTACEA—BRANCHIOPODA CHAP. these points the eyes of the Limnadiidae are intermediate between those of Apus and those of the Cladocera. Dorsal Organ.—A_ structure very characteristic of adult Phyllopods is the “ dorsal organ ” (Figs. 2, 5, D.O), whose function is in many cases obscure. It is always a patch of modified cephalic ectoderm, supplied by a nerve from the anterior ventral lobe of the brain on each side; but its characters, and apparent function, differ in different forms. In the Branchipodidae the dorsal organ is a circular patch, far forward on the surface of the head (Figs. 2, 5, D.O). Its cells are arranged in groups, which remind one of the retinulae in a compound eye; each cell contains a solid concretion, and the concretions of a group may be so placed as to look like a badly-formed rhabdom. Claus,’ who first called attention to this structure in the Branchipodidae, regarded it as a sense-organ. In Apodidae the dorsal organ is an oval patch of columnar ectoderm, immediately behind the eyes ; it is slightly raised above the surrounding skin, and is covered by a very delicate cuticle (with an opening to the exterior ?), and below it is a mass of connective tissue permeated by blood; Bernard has suggested that it is an excretory organ. Most Limnadiidae resemble the Cladocera in the possession of a “ dorsal organ” quite distinct from the above; in Limnetis and Estheria it has the form of a small pit, lined by an apparently glandular ectoderm, and this is its condition in many Cladocera ; in Limnadia lenticularis it is a patch of glandular epithelium on a raised papilla. Limnadia has been observed to anchor itself to foreign objects by pressing its dorsal organ against them, and many Cladocera do the same thing; Sida erystallina, for example, will remain for hours attached by its dorsal organ to a water- weed or to the side of an aquarium. Structures resembling a dorsal organ occur in the larvae of many other Crustacea, but the presence of this organ in the adult is confined to Branchiopods. and indeed in many Cladocera it disappears before maturity. It is certain that the sensory and adhesive types of dorsal organ are not homologous, especially as rudimentary sense-organs may exist on the head of Cladocera together with the adhesive organ. The telson differs considerably in the different genera. In the Branchipodidae* the anus opens directly backwards; and 1 Arb. zool. Inst. Wien, vi., 1886, p. 267. * I do not understand Packard’s account of the telson in Thamnocephalus. II TELSON ‘OF PHYLEORODA 24723 the telson carries two flattened backwardly - directed plates, one on each side of the anus, the margins of each plate being fringed with plumose setae. In Artemia the anal plates are rarely as large as in Sranchipus, and never have their margins completely fringed with setae; in A. salina from Western Hurope, and in A. fertilis (Fig. 4, A) from the Great Salt Lake of Utah, there is a variable number of setae round the apical half of each lobe, but in specimens of A. salina from Western Siberia the number of setae may be very small, or they may be absent; in the closely allied 4A. wrmiana from Persia the anal lobes are well developed in the male, each lobe bearing a Fic. 4,—A, Ventral view of the anal region in Artemia fertilis, from the Great Salt Lake ; B, ventral view of the telson and neighbouring parts of Lepidurus productus ; C, side view of the telson and left anal lobe of Hstheria (sp. 2). single terminal hair, but they are altogether absent in the female. Schmankewitch and Bateson have shown that there is a certain relation between the salinity of the water in which Artemia salina occurs and the condition of the anal lobes, specimens from denser waters having on the whole fewer setae ; the relation is, however, evidently very complex, and further evidence is wanted before any more definite statements can be made. In the Apodidae the anal lobes have the form of two jointed cirri, often of considerable length ; in Apus the anus is terminal, but in Lepidurus (Fig. 4, B) the dorsal part of the telson is prolonged backwards, so as to form a plate, on the ventral face of which the anus opens, much as in the Malacostraca. In the Limnadidae (Fig. 4, C) the telson is laterally com- 24 CRUSTACEA—-BRANCHIOPODA CHAP. pressed and produced, on each side of the anus, into a flattened, upwardly curved process, sharply pointed posteriorly, and often serrate ; the anal lobes are represented by two stout curved spines, while in place of the dorsal prolongation of Lepidurus we find two long plumose setae above the anus. In the characters of the telson and anal lobes, as in those of the head, the Limnadiidae approxi- mate to the Cladocera. In Limnetis brachyura the ventral face of the telson is produced into a plate projecting backwards below the anus, in a manner which has no exact parallel among other Crustacea. The appendages of the Phyllopoda are fairly uniform in Fia. 5.—Chirocephalus diaphanus, male. Side view of head, showing the large second antenna, A, with its appendage Ap, above which is seen the filiform first antenna ; D.O, dorsal organ ; /), median eye. character, except those affected by the sexual dimorphism, which is usually great. Of the cephalic appendages, the first antennae are generally small, and are never biramous; in Branchipus and its allies they are simple unjointed rods, in some species of Artemia they are three-jointed, in Apus they are feebly divided into two joints, while in Hstheria they are many-jointed. The second antennae are the principal organs of locomotion in the Limnadiidae, where they are large and biramous; in all other Phyllopoda they are uniramous in the female, being either unjointed triangular ote II APPENDAGES OF PHYLLOPODA 25 plates as in Chirocephalus (Fig. 2), or minute vestigial fila- ments as in Apus, in which genus Zaddach, Huxley, and Claus have all failed to find any trace of a second antenna in some females. In the male Branchipodidae the second antennae are modified to form claspers, by which the female is seized, the various degrees of complication which these claspers exhibit affording convenient generic characters. In Branchinecta each second antenna is a thick, three-jointed rod, the last joint forming a claw, while the second joint is serrate on its Inner margin ; in Lranchipus the base is much thickened, and bears on its inner side a large filament (perhaps represented by the proxi- mal tubercle of Lranchinecta and Artemia), which looks hike an extra antenna. In Streptocephalus the terminal joint of the antenna is bifid, and there is a basal filament hike that of Sranchipus , in Chirocephalus diaphanus (Figs. 5, 6) the main branch of the antenna consists of two large joints, the terminal joint being a strong claw with a serrated process at its base, ae ; ; ’ ‘ ‘ oe Fic. 6.—Chirocephalus diaphanus. Second while the proximal joint antenna of male, uncoiled. bears two appendages on its inner side; one of these is a small, subconical tubercle, the second is more complicated, consisting of a main stem and five outgrowths. The main stem is many-jointed and flexible, its basal joint being longer than the others, and bearing on its outer side a large, triangular, membranous appendage, and four soft cylindrical appendages, the main stem and its appendages being beset with curious tubercles, ending in short spines, whose structure is not understood. Except during the act of copulation this remarkable apparatus is coiled on the inner side of the antennary claw, the jointed stem being so coiled that it is often compared to the 20 CRUSTACEA—BRANCHIOPODA CHAP. coiled proboscis of a butterfly, and the triangular membrane folded like a fan beside it, so that much of the organ is concealed, and the general appearance of the head is that shown in Fig. 5. During copulation, the whole structure is widely extended. The males of Artemia (Fig. 7) have the second antenna two- jointed, the basal joint bearing an inner tubercle, the terminal joint being flattened and bluntly pointed, its outer margin provided with a membranous outgrowth. In A. fertilis the breadth of the second joint varies greatly, the narrower forms pre- senting a certain remote resemblance to Fic. 7.—Artemia fertilis, Front view of the head of a branchinecta. In the ores he large second antennae, A.2; males of Polyartemia A.1, first antennae. the second antennae have a remarkable branched form not easily comparable with that found in other Branchipodidae. The cephalic jaws are fairly uniform throughout the order. The mandibles have an undivided molar surface, and no palp ; the first maxilla is very generally a triangular plate, with a setose biting edge; mandibles and maxillae are covered by the labrum. The second maxilla generally lies outside the chamber formed by the labrum, and is a simple oval plate, with or without a special process for the duct of the kidney. The thoracic limbs, in front of the genital segments, are not as a rule differentiated into anterior maxillipedes and posterior locomotive appendages, as in higher forms; we have seen, however, that all these limbs take part in the prehension of food, and except in the Limnadiidae they all assist in locomotion. One of the middle thoracic legs of Artemia (Fig. 8, A) has a flattened stem, with seven processes on its inner, and two on its outer margin. The gnathobase (gn) is large, and fringed with long plumose setae, each of which is jointed; this is followed by four smaller “ endites” (or processes on the median side), and then by two larger ones, the terminal endite (the sixth, II APPENDAGES OF PHYLLOPODA 277, excluding the gnathobase) being very mobile and attached to the main stem by a definite joint. On the outer side are two pro- cesses ; a proximal “bract,” a flat plate with crenate edges, partly divided by a constriction into two, and a distal process, cylindrical and vascular, called by Sars and others the “epipodite.” In other Branchipodidae we have essentially the same condition, except that the fifth endite often becomes much larger than in Artemia, throwing the terminal endite well over to the outer A B Fic. 8.—A, Thoracie limb of Ch irocephalus diaphanus ; B, prehensile thoracic limb of male Estheria. gn, Gnathobase ; 1-6, the more distal endites. edge of the limb; such a shift as this, continued farther, might well lead to the condition found in the Limnadiidae, or Apodidae, where the lobe which seems to represent the terminal endite of Artemia is entirely on the outer border of the limb, forming what most writers have called the exopodite (Lankester’s “flabellum ”)." In the two last-named families the basal exite or bract of the Branchipodidae does not appear to be represented. The limbs of the Apodidae are remarkable in two ways: those in front of thé genital opening (very constantly ten pairs) ' The nomenclature here adopted is not that of Lankester. 28 CRUSTACEA—-BRANCHIOPODA CHAP. are not so nearly alike as in most genera of the sub-order, the first two pairs especially having the axis definitely jointed, while the endites are elongated and antenniform; further, while the first eleven segments bear each a single pair of limbs, as is usual among Crustacea, many of the post-genital segments bear several pairs; thus in Apus caneriformis there are thirty-two post- cephalic segments in front of the telson, the first eleven having each one pair of limbs, while the next seventeen have fifty-two pairs between them, the last four segments having none. Tu all the Phyllopoda some of the post-cephalic limbs are modified for reproductive purposes; in the Branchipodidae the last two pairs (the 12th and 13th generally, the 20th and 21st in Polyartemia) are so modified in both sexes. In the female these appendages fuse at an early period of larval life, and surround the median opening of the generative duct (Fig. 2); in the male the two pairs also fuse, but traces of the limbs are left as eversible processes round the paired openings of the vasa deferentia. In the other families, one or more limbs of the female are adapted for carrying or supporting the eggs. In the Apodidae the appendages of the eleventh segment have the exopodite in the form of a rounded, watchglass-shaped plate, fitting over a similarly shaped process of the axis of the limb, so that a lens- shaped box is formed, into which the eggs pass from the oviduct. In Limnadiidae the eggs are carried in masses between the body and the carapace, and are kept in position by special elongations of the exopodites of two or three legs, either those near the middle of the thorax (Hstheria, Limnadia), or at its posterior end (Limnetis). In female LZimnetis the last thoracic segments bear two remarkable lateral plates, which apparently also help to support the eggs. In the male Limnadiidae, the first (Limnetis) or the first two thoracic feet (Zimnadia, Estheria) are prehensile (Fig. 8, B). Alimentary Canal.— The mouth of the Phyllopoda is overhung by the large labrum, so that a kind of atrium is formed, outside the mouth itself, in which mastication is per- formed ; numerous unicellular glands, opening on the oral face of the labrum, pour their secretion into the atrial chamber, and may be called salivary, though the nature of their secretion is not known. The mouth has commonly two swollen and setose II ALIMENTARY CANAL AND HEART 29 lips, running longitudinally forwards from the bases of the first maxillae, and often wrapping round the blades of the mandibles. It leads into a vertical oesophagus, which opens into a small globular stomach, lying entirely within the head; the terminal part of the oesophagus is slightly invaginated into the stomach, so that a valvular ring is formed at the junction of the two. The stomach opens widely behind into a straight intestine, which runs backwards to about the level of the telson, where it joins a short rectum, leading to the terminal or ventral anus. The stomach and intestine are ned by a columnar epithelium, and covered by a thin network of circularly arranged muscle-fibres; the rectum has a flatter epithelium, and radial muscles pass from it to the body-wall, so that it ean be dilated. The only special digestive glands are two branched glandular tubes, situated entirely within the head, which open into the stomach by large ducts, one on each side. In Chirocephalus the gastric glands are fairly small and simple; in the Apodidae their branches are more complex and form a considerable mass, filling all that portion of the head which is not occupied by the nervous system and the muscles. Backwardly directed gastric glands, like those of the higher Crustacea, are not found in Branchiopods ; both forms occur together in the genus Nebalia, but with this exception the forwardly directed glands are peculiar to Branchiopods. Heart.—In Branchipus and its allies, and in Artemia, the heart extends from the first thoracic segment to the penultimate segment of the body, and is provided with eighteen pairs of lateral openings, one pair in every segment through which it passes except the last; it 1s widely open at its hinder end, and is prolonged in front for a short distance as a cephalic aorta, the rest of the blood-spaces being lacunar. In most, at least, of the other Branchiopods, the heart is closed behind and is shortened; in Apus and Lepidurus it only extends through the first eleven post-cephalic segments, while in the Limnadiidae it is shorter still, the heart of Zimnetis passing through four segments only. In all cases there is a pair of lateral openings in every segment traversed by the heart. The blood of the Branchipodidae and Apodidae contains dissolved haemoglobin, the quantity present being so small as to give but a faint colour to the blood in Branchipus, while 30 CRUSTACEA—BRANCHIOPODA CHAP. Artemia has rather more, and the blood of Apus is very red. The only other Crustacea in which the blood contains haemo- globin are the Copepods of the genus Lernanthropus,’ so that the appearance of this substance is as irregular and inexplicable in Crustacea as in Chaetopods and Molluscs. The nervous system of Branchipus may be described as an illustration of the condition prevailing in the group. The brain consists of two closely united gangha, in each of which three main regions may be distinguished; a ventral anterior lobe, a dorsal anterior lobe, and a posterior lobe. The ventral anterior lobes give off nerves to the median eye, to the dorsal organ, and to a pair of curious sense-organs, comparable with the larval sense-knobs of many higher forms, situated one on each side of the median eye; in late larvae Claus describes the terminal apparatus of each frontal sense-organ as a_ single large hypodermic cell; W. K. Spencer” has lately described several terminal cells, containing peculiar chitinous bodies, in the adult. The homologous sense-organs of Limnetis are appar- ently olfactory. The dorsal anterior lobes give off the large nerves to the lateral eyes, while the posterior lobes supply the first antennae. The oesophageal connectives have a coating of ganglion-cells, and some of these form the ganglion of the second antenna, the nerve to this appendage leaving the con- nective just behind the brain. The post-oral nerve-cords are widely separate, each of them dilating into a ganglion opposite every appendage, the two ganglia being connected by two transverse commissures. The ganglia of the three cephalic jaws, so often fused in the higher Crustacea, are here perfectly distinct. Closely connected with each thoracic ganghon is a re- markable unicellular gland, opening to the exterior near the middle ventral line; it is conceivable that these cells may be properly compared with the larval nephridia of a Chaetopod,” but no evidence in support of such a comparison has yet been adduced. Behind the genital segments, where there are no limbs, the nerve-cords run backwards without dilating into segmental ganglia, except in the anterior two abdominal segments where ‘(The red pigment in Lernanthropus, see p. 68, has been shown to be not haemoglobin, so that the presence of this substance in Phylopod blood becomes doubtful.—G.8. ] 2 Zeitschr. wiss. Zool. \xxi., 1902, p. 508. 3 Cf. Gaskell, Journ. Anat. Physiol. x., 1876, p. 153, II REPRODUCTIVE ORGANS ios) = small ganglionic enlargements occur. In Apodidae, on the other hand, those segments which carry more than one pair of appendages have as many pairs of ganglia, united by transverse commissures, as they have limbs. A stomatogastric nervous system exists in dApus, where a nerve arises on each side from the first post-oral commissure, and runs forward to join its fellow of the opposite side on the anterior wall of the oesophagus. From the loop so formed a larger median and a series of smaller lateral nerves pass to the wall of the alimentary canal. A second nerve to the oesophagus is given off from the mandibular ganglion of each side. Reproductive Organs.—In Chirocephalus the ovaries (Fig. 2, Ov) are hollow epithelial tubes, lying one on each side of the alimentary canal, and extending from the sixth abdominal seoment forwards to the level of the genital opening ; at this point the two ovaries are continuous with ducts, which bend sharply downwards and open into the single uterus contaimed within the projecting egg-pouch and opening to the exterior at the apex of that organ. Short diverticula of the walls of the uterus receive the ducts of groups of unicellular glands, the bodies of which contain a peculiar opaque secretion, said to form the egg- shells. In Apodidae the ovaries are similar in structure, but they are much larger and branch in a complex manner, while each ovary opens to the exterior independently of the other in the eleventh post-cephalic segment; nothing hke the median uterus of the Branchipodidae being formed. The epithelium of the ovarian tubes proliferates, and groups of cells are formed ; one becoming an ovum, the others being nutrient cells like those which will be more fully described in the Cladocera. In Chirocephalus the testes are tubes similar in shape and position to the ovaries, each communicating in front with a short vas deferens, which dilates into a vesicula seminalis on its way to the eversible penis; an essentially similar arrangement is found in all Branchipodidae, but in Apodidae and Limnadiidae there is no penis. All the Branchiopoda are dioecious,’ and many are partheno- genetic. Among Branchipodidae Artemia is the only genus known to be parthenogenetic, but parthenogenesis is common in 1 Bernard’s statement that Apus is hermaphrodite seems based on insufficient evidence. 32 CRUSTACEA—BRANCHIOPODA CHAP. all Apodidae, while the’ males of several species of Zimnadia are still unknown, although the females are sometimes exceedingly common. In Artemia, generations in which the males are about as numerous as the females seem to alternate fairly quickly with others which contain only parthenogenetic females; in Apus males are rarely abundant, and often absent for long periods; during five consecutive years von Siebold failed to discover a male in a locality in Bavaria, though he examined many thousands of individuals; near Breslau he found on one occasion about 11 per cent of males (114 in 1026), but in a subsequent year he found less than 1 per cent; the greatest recorded percentage of males is that observed by Lubbock in 1863, when he found 33 males among 72 individuals taken near Rouen. The eggs of most genera can resist prolonged periods of desiccation, and indeed it seems necessary for the development of many species that the eggs should be first dried and afterwards placed in water. Many eggs (eg. of Chirocephalus diaphanus and Branchipus stagnalis) float when placed in water after desic- cation, the development taking place at the surface of the water. Habitat.— All the Phyllopoda, except Artemia, are confined to stagnant shallow waters, especially to such ponds as are formed during spring rains, and dry up during the summer. In waters of this kind the species of Branchipus, Apus, etc., develop rapidly, and produce great numbers of eggs, which are left in the dried mud at the bottom after evaporation of the water, where they reinain quiescent until a fresh rainy season. The mud from the beds of such temporary pools often contains large numbers of egos, which may be carried by wind, on the legs of birds, and by other means, to considerable distances. Many exotic species have been made known to European naturalists by their power of hatching out when mud brought home by travellers is placed in water. The water of stagnant pools quickly dissolves a certain quantity of solid matter from the soil, and often receives dissolved solids through surface drainage from the neighbouring land; such salts may remain as the water evaporates, so that the water which remains after evaporation has proceeded for some time may be very sensibly denser than that in which the Branchiopods were hatched; these creatures must therefore be able to endure a con- siderable increase in the salinity of the surrounding waters during II HABITAT OF PHYLLOPODA ios) ios) the course of their lives. My friend Mr. W. W. Fisher points out that the plants present in such a pond would often precipitate the carbonate of lime, so that this might be removed as evapora- tion went on, but that chlorides would probably remain in solu- tion; from analyses which Mr. Fisher has been kind enough to make for me, it is seen that this happened in a small aquarium in my laboratory, in which Chirocephalus diaphanus lived for four months. In April, mud from the dry bed of a pond, known to contain eggs of Chirocephalus, was placed in this aquarium in Oxford, and water was added from the tap. Oxford tap-water contains about 0°3 grm. salts per litre, the chlorine being equiva- lent to 0°025 orm. NaCl. Water was added from time to time during May and June, but in July evaporation was allowed to proceed unchecked. At the end of July there was about half the original volume of water, the Chirocephalus being still active ; the residue contained 0°96 germ. dissolved solids per litre, with chlorine equal to 0°19 grm. NaCl, so that the percentage of chlorides was about eight times the initial percentage, but there were only three and a fifth times the original amount of total solid matter in solution, the carbonate of lime having pre- cipitated as a visible film. Some species of Branchipus (e.g. B. spinosus, M. Edw.) and of Estheria (EF. macgillivrayi, Baird, F. gubernator, Klutzinger) occur in salt pools, but Artemia flourishes in waters beside whose salinity that endured by any other Branchiopod is in- significant. In the South of Europe, Artemia salina may be found in swarms, as it used to be found in Dorsetshire, in the shallow brine-pans from which salt is commercially prepared ; Rathke quotes an analysis showing that a pool in the Crimea contained living Artemia when the salts in solution were 271 grms. per litre, and the water was said to have the colour and consistency of beer. The behaviour of the animals in the water differs a little; in normal feeding all the species swim with the back downwards, as has already been said; the Branchipodidae rarely settle on the ground, or on foreign objects, but the Apodidae occasionally wriggle along the bottom on their ventral surface, and Zstheria burrows in mud. The greater number of species are found in pools in flat, low- lying regions, and many appear to be especially abundant near VOL. IV D 34 CRUSTACEA—BRANCHIOPODA CHAP. the sea; Apus cancriformis has, however, been found in Armenia at 10,000 feet above sea-level. Wells and underground waters do not generally contain Phyllopods; but a species of Branchipus and one of Limnetis, both blind, have been described from the caves of Carniola. One of the many puzzles presented by these creatures is the erratic way in which they are scattered through the regions they inhabit ; a single small pond, a few yards or less in diameter, may be the only place within many miles in which a given species can be found; in this pond it may, however, appear regularly season after season for some time, and then suddenly vanish. Geographically, the Phyllopoda are cosmopolitan, represen- tatives of every family and of some genera (e.g. Streptocephalus, Lepidurus, Estheria) being found in every one of the great zoo- logical regions, though a few aberrant genera are of limited range, thus Polyartemia is known only from the northern Palaearctic and Nearctic regions, Zamnocephalus only from the Central United States. The genus Artemia is not at present known in Australia.’ The only recorded British species are Chirocephalus diaphanus, Artemia salina, and Apus cancriformis, but other continental islands, for example the West Indian group, are better supplied. The distribution of the species is very im- perfectly known, but on the whole every main zoological region seems to have its own peculiar species, which do not pass beyond its boundaries. Branchinecta paludosa and Lepidurus glacialis are circumpolar, both occurring in Norway, in Lapland, in Greenland, and in Arctic North America; but with these exceptions the Palaearctic and Nearctic species seem to be distinct. The Euro- pean species Apus cancriformis occurs in Algiers, but the relations between. the species of Northern Africa as a whole and those of Southern Europe on the one hand, or of Central and Southern Africa on the other, have yet to be worked out. The .soft-bodied Branchipodidae are not known in the fossil condition ;* an Apus, closely related to the modern A. cancriformis, has been found in the Trias, but the most numerous remains have been left, as might be expected, by the hard-shelled Limnadidae ; 1 Sayce has since described it, Proc. Roy. Soc. Victoria, xv., 1903, p. 229. 2 A. cancriformis had been supposed to have disappeared from the British fauna for many years, but it was found in Scotland in 1907, See R. Gurney, Vature, Ixxvi., 1907, p. 589. 5 Branchipodides has been described by H. Woodward, from Tertiary strata. HI GENERA OF PHYLLOPODA 35 earapaces, closely resembling those of the modern Hstheria, are known in beds of all ages from the Devonian period to recent times; these carapaces are in several cases associated with fossils of an apparently marine type. None of the fossil species differ in any important characters from those now living, so that the Phyllopoda have existed in practically their present form for an enormously long period; this fact, and the evidence that species of existing genera were at one time marine, explain the wide distribution of animals at present restricted to a remarkably limited range of environmental conditions. Summary of the Characters of the Genera. Sus-ORDER PHyLLorpopsa.—BPranchiopoda with an elongated body, pro- vided with at least ten pairs of post-cephalic limbs, the heart extending through four or more thoracic segments, and having at least four pairs of ostia. Fam. 1. Branchipodidae.'—Carapace rudimentary, eyes stalked; the second antennae flat and unjointed in the female, jointed and prehensile in the male ; female generative opening single; telson not laterally compressed, bearing two flattened lobes, or none. The heart extending through the thorax and the greater part of the abdomen. A. Eleven pairs of praegenital ambulatory limbs. a. Abdomen of six well-formed segments and a telson; anal lobes well formed, their margins setose. Branchinecta, Verrill—Second antennae of ¢ without lateral appendages ; ovisac of 9 elongated. B. paludosa, O. F. Miull.— Circumpolar. Branchiopodopsis, G. O. Sars?—Second antennae of ¢ as in Branchinecta ; ovisac of Q short. B. hodgsoni, G. O. Sars —Cape of Good Hope. Branchipus, Schaeffer—Second antennae of ¢ with simple internal filamentous appendage. JB. stagnalis, Linn. — Central Europe. Streptocephalus, Baird—Second antennae of ¢ 3-jointed, the last joint bifid; an external filamentous appendage. ¥. torvicornis, Wagn., Poland. Chirocephalus, Prévost—Second antennae of ¢ 3-jointed, witha jointed internal appendage, which bears secondary processes, four cylindrical and one lamellar. ©. diaphanus, Prévost (Fig. 2, p. 20).—Britain, Central Europe. b. Abdominal segments five or fewer, and a telson. Anal lobes small or 0, sparsely or not at all setose. Artemia, Leach—Second antennae of g without filamentous /; Consult Baird, ‘‘ Monograph of the Branchiopodidae,” Proc. Zool. Soc. 1852, p. 18. Packard, 12th Ann. Rep. U.S. Geol. Survey, part 1., 1879. 2 Arch. f. Math. og Naturvidensk. xx., 1898, Nos. 4 and 6. Thiele, Zool. Jahrb. System. xiii., 1900, p. 568. 36 CRUSTACEA—BRANCHIOPODA CHAP, appendage, 2-jointed, the second joint lamellar. A. salina, Linn.—Brine pools of the Palaearctic region. c. Hinder abdominal segments united with telson to form a fin; anal_ lobes absent. Thamnocephalus, Packard—Head with a branched median pro- cess of unknown nature. Only species 7. platywrus, Packard —Kansas, U.S.A. B. Nineteen pairs of praegenital ambulatory limbs. Polyartemia, Fischer—Second antennae of ¢ forcipate ; ovisae of @ very short Only species P. forcipata, Fisch. Fam. 2. Apodidae.'—Carapace well developed as a depressed shield, covering at least half the body. Eyes sessile, covered; no male clasping organs ; anal lobes long, jointed cirri. Apus, Scopoli—tTelson not produced backwards over the anus ; endites of first thoracic limb very long. *+ In the greater number of Daphniidae, the parthenogenetic female, produced from a winter-egg, gives rise only to parthenogenetic forms, and it is not until after half a dozen parthenogenetic generations have been produced that a few sexual forms appear, mixed with the others. Such sexual forms are fairly common in April or May in this country; they produce “winter” eges and then die, the generations which succeed them through the summer being entirely parthenogenetic. In late autumn sexual individuals are again produced, giving rise to a plentiful crop of winter-eggs, but many parthenogenetic females ‘are still found, and some of these appear to live and to re- Bp oduce through the winter. / ~ In Sida, in the Polyphemidae and Leptodoridae, and in most of the Lynceidae, sexual individuals are produced only once in every year, while in a few forms which inhabit great lakes the sexual condition occurs so rarely that it is still unknown. Weismann’ has pointed out that the sexual forms, with their property of producing eggs which can endure desiccation, recur most frequently in species such as J/oina, which inhabit small pools liable to be dried up at frequent intervals, while the 1 Zeitschr. wiss. Zool. xxvii., Xxxiil., 1876, 1879. VOL. IV E 50 CRUSTACEA—BRANCHIOPODA CHAP. species which produce sexual forms only once a year are all inhabitants either of great lakes which are never dry, or of the sea. Many suggestions have been made as to the environmental stimulus which induces the production of sexual individuals, but nothing is definitely known upon the subject. We have said that even in those generations which contain sexual males and females there are always some parthenogenetic individuals; there is therefore nothing in the behaviour: of Daphniidae, either under natural conditions or when observed in aquaria, to suggest that there is any natural or necessary limit to the number of generations which may be parthenogenetically produced. The parthenogenetic Daphniidae are extremely sensitive to changes in their surroundings; small variations in the character and amount of substances dissolved in the water are often followed by changes in the length of the posterior spine, in the shape and size of crests on the head, and in other characters affecting the appearance of the creatures, so that the deter- mination of species is often a matter of great difficulty. It is remarkable that the green light which has passed through the leaves of water-plants appears to have a prejudicial effect upon some species. Warren has shown that Daphnia magna repro- duces more slowly when exposed to green light, and that in- dividuals grown in this way are more readily susceptible to injury from the presence of small quantities of salt (sodium chloride) in the water than individuals which have been exposed to white light. The majority of the Cladocera belong to the floating fauna of the fresh waters and seas; a few are littoral in their habits, clinging to water-weeds near the shore, a very few live near the bottom at considerable depths, but the majority belong to that floating fauna to which Haeckel gave the name of “ plankton.” The Crustacea are an important element in the plankton, Whether in fresh waters or in the sea, the two great groups Which contribute most largely to it being the Cladocera and the Copepoda. For this reason it will be more convenient. to discuss the habits and distribution of individual Cladocera and Copepoda together in a chapter specially devoted to the characters of pelagic faunas (¢f. Chap. VIT.). We will only add to the present chapter a table of the families with a diagnosis of the British genera. II BRITISH GENERA OF CLADOCERA iy i Summary of Characters of the British Genera.’ Tribe I. Catypromera, Sars.—The post-cephalic portion of the body enveloped in a free fold or carapace. A. Six pairs of thoracic feet, the first pair not prehensile (CTENOPODA). Fam. 1. Sididae: second antennae biramous in both sexes. Sida, Straus (Fig. 11): second antenna with three joints in the dorsal ramus, two in the ventral; the rostrum large, the teeth on the telson many. Latona, Straus: second antenna with two joints in the dorsal ramus, three in the ventral, the proximal joint of the dorsal ramus provided with a setose appendage. Daphnella, Baird: second antenna with the joints as in Latona, but with no setose appendage. Fam. 2. Holopediidae: second antennae not biramous in the female; a rudimentary second ramus in the male. Holopediwm, Zaddach. B. Four to five or six pairs of thoracic feet, the anterior pair prehensile (ANOMOPODA). A. Ventral ramus of second antenna with three joints, the dorsal ramus with four. Fam. 3. Daphniidae: five pairs of thoracic feet, with a gap between the fourth and fifth pairs. The stomach with two forwardly-directed diverticula. i. First antennae of female short. a A median dorsal spine on posterior margin of carapace. Daphnia, O. F. Miller (Fig. 19): first antennae of female not mobile. The head separated from the thorax only by Fie. 19. — Daphnia obtusa, male, x about 50. Oxford. A.1, First an- tenna; Z7h.1, first thoracic append- age. a slight constriction or not at all. Cuticle with a quadrate rhomboid pattern. Ceriodaphnia, Dana: first antennae of 1 Consult Lilljeborg, Nov. Acta Reg. Soc. Upsalensis, 1901; Scourfield, J. Quekett Micr. Club, 1903-4. 2 CRUSTACEA—BRONCHIOPODA CHAP. female mobile. The head separated by a deep depression from the thorax. Cuticle with a polygonal pattern. £ A pair of ventral spines on posterior margin of carapace. Scapholeberis, Schoedler (Vig. 20). Fic. 20. — Scaphole- beris mucronata, female, ahaa Oxford. y No spine on posterior margin of carapace. Simocephalus, Schoedler (Fig. 10, p. 39): the cuticle with a pattern of parallel branching ridges. Fia. 21.—Moina rectirostris, female, x 24. Oxford. ii, First antennae of female long, mobile. Mozna, Baird (Figs. 16, 17, 21): median eye absent. Posterior margin of carapace without a spine. Fic. 22,—Bosmina sp., female, x about Kia, 23.—Acroperus leucocephalus, 80. Lake Constance. x about 35. Oxford. II FAMILIES OF CLADOCERA 53 Fam. 4. Bosminidae:. feet equidistant, five or six pairs; the first antennae of the female immobile, with sense-hairs arranged in rings, not forming an apical tuft. The intestine uncoiled; no caeca. Bosmina, Baird (Fig. 22). Fam. 5. Lyncodaphniidae : four, five, or six pairs of equidistant thoracic limbs; the first two pairs prehensile. First antennae of female mobile, with apical sense-hairs. Intestine coiled or straight. i. Four pairs of thoracic limbs. Lathonura, Lilljeborg. ii. Five pairs of thoracie limbs. a. The four-jointed ramus of the second antenna with four swimming hairs. Macrothriz, Baird: the first antennae of the female flattened, curved. The intestine simple, straight. Streblocerus, Sars: first antennae of the female very little flattened, curved backwards and outwards. The intestine coiled, the stomach with two forwardly-directed caeca, ; 6. The four-jointed ramus of the second antenna with only three swimming hairs. Drepanothrix, Sars. iii. Six pairs of thoracic limbs; the labrum provided with an appendage, Acantholeberis, Lilljeborg: appendage of labrum long, pointed, and _ setose. Intestine without caecum. Ilyocryptus, Sars: appendage of the labrum short, truncated. Intestine with a caecum. B. Both rami of second antenna three-jointed. Fam. 6. Lynceidae': five or six equidistant pairs of thoracic feet. Intestine coiled. 1, Six pairs of thoracic limbs. Head and thorax separated by a deep depression. Intestine with one caecum, stomach with two. Female carries many summer-eges. Ewrycercus, Baird. il, Five pairs of thoracic limbs. Head and thorax separated by a slight groove or not at all. Anterior digestive caeca absent. Female carries only one or two summer-eggs. A. Body elongate, oval. a. Head carinate, the eye far from the anterior cephalic margin. Camptocercus, Baird: body laterally compressed. Second antennae with seven swimming hairs. 'Telson more than half as long as the shell. Acroperus, Baird (Fig. 23): body compressed. Second antennae with eight swimming hairs, of which one is very small. Telson less than half as long as the shell. 6. Head not carinate, the eye near the anterior cephalic margin. Alonopsis, Sars: terminal claws of telson with three accessory teeth. Alona, Baird: terminal claws of telson with one accessory tooth (includes sub-genera Leydigia, Alona, Harpo- rhynchus, Graptoleberis). Peracantha, Baird (Fig. 14): terminal ' More properly Chydoridae, but the universally known name Lynceidae is con- venient. 54 CRUSTACEA——BRA NCHIOPODA CHAP. II claws of telson with two accessory teeth (includes sub-genera Alonella, Pleuroxus, Peracantha). B. Body small, spheroidal ; the head depressed. Chydorus, Leach: compound eye present. Monopsilus, Sars: compound eye absent. Tribe II. Gymnomera, Sars.—The carapace forms a closed brood-pouch, which does not cover the body ; all the thoracic limbs prehensile. Fam. 7. Polyphemidae: four pairs of thoracic limbs, provided with a gnathobase. Fresh-water genera.—Polyphemus, Miller, with no rudimentary exites on first three thoracic limbs. Bythotrephes, Leydig (Fig. 13), with no trace of processes on the outer sides of the limbs. Marine genera.—Evadne, Lovén, the head not separated by a constriction from the thorax.* Podon, Lovén, with deep cervical constriction. Fia. 24.—Leptodora hyalina, x 6. Lake Bassenthwaite. A.1, First antenna ; Car, carapace ; I, VI, first and sixth thoracic appendages. Fam. 8. Leptodoridae : six pairs of thoracic limbs, with no gnathobase. Only genus, Leptodora, Lilljeborg (Fig. 24), from fresh water. Note.—For extra- European Cladocera consult Daday, ‘“ Microskopische Stisswassertiere aus Patagonien und Chili,” Termés Fiizetek, xxv., 1902, p. 201; for Paraguay, Bibliotheca Zoologica, Heft 44 ; for Ceylon, Termés Fiizetek, xxi, 1898; and for Australia, Sars, Christiania Vidensk. Forhand. 1885, No. 8, and 1888, No. 7; and Arch. f. Math. 0g Naturvid. xviii. 1896, No. 3, and-xix., 1897, No. 1.—G. W. S. CHAPTER III CRUSTACEA (CONTINUED): COPEPODA Order II. Copepoda. THE Copepods are small Crustacea, composed typically of about sixteen segments, in which the biramous type of limb _ pre- dominates. They are devoid of a carapace. Development proceeds gradually by the addition posteriorly of segments to a Nauplius larval form. Paired compound eyes are absent, except in Branchiura, the adult retaining the simple eye of the Nauplius. | In a typical Copepod, such as Calanus hyperboreus (Fig. 25), we can distinguish the following segments with their appen- dages: a cephalothorax, carrying a pair of uniramous first an- tennae (7% Ant.) ; a pair of biramous second antennae (2 Ant.) ; mandibles (J/d.) with biting gnathobases and a palp, and a pair of foliaceous first maxillae (MJw.!). Two pairs of appendages follow, which were looked upon as the two branches of the second maxillae, but it is now certain that they represent two pairs of appendages, which may be called second maxillae (Mz.”), and maxillipedes (Map.) respectively. Behind these are five pairs of biramous swimming feet, the first pair (Zv.*) attached to the cephalothorax, the succeeding four pairs to four distinct thoracic somites. Behind the thorax is a clearly delimited abdomen composed of five segments, the first of which (Abd.") carries the genital opening, and the last a caudal furca. The Copepods exhibit a great variety of structure, and their classification is attended with great difticulties. Claus? based his attempt at a natural classification on the character of 1 Grundzxiige der Zoologie, 4. Aufl. 1880, p. 543. 55 56 CRUSTAGCHA——COPREPODA CHAP. the mouth and its appendages, dividing the free-living and semi-parasitic forms as Gnathostomata from the true parasites or etal lie SEE |, = W ay went 2ndAnt eT JI-y = SS) ae y----Abd.?. Fic, 25.—Calanus hyperboreus, x 30. Abd}, First abdominal segment; Jst Ant, 2nd Ant, Ist and 2nd antennae ; Md, mandible ; Ma, Mx?, 1st and 2nd maxillae ; Map, maxillipede ; Th!, Ist thoracic appendage. (After Giesbrecht.) Siphonostomata. This division, although convenient, breaks down in many places, and it is clear that the parasitic mode of life has been acquired more than once in the history of Copepod Ill EUCOPEPODA—GYM NOPLEA—AMPHASCANDRIA 57 evolution, while the free-living groups do not constitute a natural assemblage. Giesbrecht has more recently ' founded a classification of the free-living pelagic Copepods upon the segmentation of the body and certain secondary sexual characters, and he has hinted * that this scheme of classification apphes to the semi-parasitic and parasitic forms. Although much detail remains to be worked out and the position of some families is doubtful, Giesbrecht’s scheme is the most satisfactory that has hitherto been suggested, and will be adopted in this chapter. The peculiarity in structure of the Argulidae, a small group of ectoparasites on fresh water fish, necessitates their separation from the rest of the Copepods (Eucopepoda) as a separate Branch, Branchiura. BRANCH I. EUCOPEPODA. Sub-Order 1. Gymnoplea. The division between the front and hind part of the body falls immediately in front of the genital openings and behind the fifth thoracic feet. The latter in the male are modified into an asymmetrical copulatory organ. TRIBE I. AMPHASCANDRIA. The first antennae of the male are symmetrical, with highly- developed sensory hairs. Fam. Calanidae.—The Calanidae are exclusively marine Crustacea, and form a common feature of the pelagic plankton in all parts of the world. Some species of the genus Calanus often occur in vast shoals, making the sea appear blood-red, and they furnish a most important article of fish food. These swarms appear to consist chiefly of females, the males being taken rarely, and only at certain seasons of the year. Some of the Calanidae are animals of delicate and curious form, owing to the development of plumed iridescent hairs from various parts of their body, which may often exhibit a marked asymmetry, as 1 Fauna and Flora G. v. Neapel, Monograph 19, 1892. 2 Ibid. Monograph 25, 1899. 58 CRUSTACEA—COPEPODA CHAP. in the species figured, Calocalanus plumulosus (Fig. 26), from the Mediterranean. Sars makes a curious observation’ with regard to the distribution of certain Calanidae. He reports that along the whole route of the “Fram,” species such as Calanus hyperboreus and Huch- aeta norwegica were taken at the surface, which, in the Nor- wegian fjords, only occur at depths of over 100 fathoms. He suggests that the Nor- wegian — individuals, instead of migrating northwards as the warmer climate super- vened, have sought boreal conditions of temperature by sinking into the deeper waters. Dy gyfer = TRIBE IL. ATA pana Na Fic, 26.—Calocalanus plumulosus, x 15. ' ; (After Giesbrecht. ) The first antennae of the male are asym- metrical, one, usually the right, being used as a clasping organ. The males of the Centropagidae, Candacidae and Pontellidae, besides possessing the asymmetrically modified thoracic limbs of the fifth pair also exhibit a modification of one of the first antennae, which is generally thickened in the middle, and has a peculiar joint in it, or geniculation, which enables it to be flexed and so used as a clasping organ for holding the female. Fam. 1.—Centropagidae.—These Copepods are very common in the pelagic plankton, and some of the species vie with the ‘ Norwegian North Polar Exp. Sei. Results, vol. i. part v., 1900. III GYMNOPLEA—HETERARTHRANDRIA 59 Calanidae in plumed ornaments, e.g. Augaptilus filigerus, figured by Giesbrecht in his monograph. The use of these ornaments, which are possessed by so many pelagic Copepods, is entirely obscure.’ Certain of the Centropagidae live in fresh water. Thus Diaptomus is an exclusively fresh-water genus, and forms a most important constituent of lake- plankton; various species of Heterocope occur in the great continental lakes, and certain Eurytemora go up the estuaries of rivers into brackish water. An excellent work on the fresh-water Copepods of Germany has been written by Schmeil,? who gives analytical tables for distinguishing various genera and species. The three fresh-water families are the Centropagidae, Cyclopidae, and Harpacticidae (see p. 62). The Centropagidae may be sharply distinguished from the other fresh-water families by the following characters :— The cephalothorax is distinctly separated from the abdomen ; the first antennae are long and composed of 24-25 segments, in the male only a single antenna (generally the right) being geniculated and used as a clasping organ. The fifth pair of limbs are not rudimentary ; a heart is present, and only one egg-sac is found in the female. The second antennae are distinctly biramous. Diaptomus.—The furcal processes are short, at most three times as long as broad; endopodite of the first swimming appendage 2-jointed, endopodites of succeeding legs 3-jointed. Heterocope.—The furcal processes are short, at most twice as long as broad ; endopodites of all swimming legs 1-jointed. Eurytemora,—The furcal processes are long, at least three and a half times as long as broad; the endopodite of the first pair of legs 1-jointed, those of the other pairs 2-jointed. It has been known for a long time that some of the marine Copepods are phosphorescent, and, indeed, owing to their numbers in the plankton, contribute very largely to bring about that liquid illumination which will always excite the admiration of seafarers. In northern seas the chief phosphorescent Copepods belong to Metridia, a genus of the Centropagidae; but in the Bay of Naples Giesbrecht’ states that the phosphorescent species are the following Centropagids : Pleuromma abdominale and P. gracile, Leuckartia flavicornis and 1 They may assist the animal by retarding its sinking. Cf. Chun, “‘ Aus den Tiefen des Weltmeeres,” 1905. 2 Schmeil, Bibliotheca Zoologica, Hefte 11, 15, and 21. ’ Giesbrecht, Mitth. Zool. Stat. Neap. xi., 1895, p. 648. 60 CRUSTACEA——COPEPODA CHAP. Heterochaeta papilligera; Oncaea conifera is also phosphorescent. It is often stated that Sapphirina (p. 69) is phosphorescent, but its wonderful iridescent blue colour is purely due to interference colours, and has nothing to do with W phosphorescence. | Giesbrecht has , observed that the phosphorescence is due to a substance secreted in special skin-glands, which is jerked into the water, and on coming into contact with it emits a phosphor- escent glow. This substance can be dried up completely in a desiccated specimen and yet preserve its phos- phorescent properties, the essential condition for the actual emission of light being contact with water. Similarly, specimens preserved in glycerine for a long period will phosphoresce when compressed in distilled water. From this last experiment Giesbrecht concludes that the phosphorescence can hardly be due to an oxidation process, but the nature of the chemical reaction remains obscure. Fam. 2. Candacidae. — This family comprises the single genus Candace, with numerous — species distributed in the plankton of all seas. Some species, e.g. C. pectinata, Brady, have a_ practically world- wide distribution, this species being recorded from the Shetlands and from the Philippines. Mayon Fam. 3. Pontellidae——This is Te! ee oe ee a larger family also comprising Sars. ) widely distributed species found in the marine plankton. Anomalo- cera pattersoni (Fig. 27) is one of the commonest elements in the plankton of the North Sea. {II PODOPLEA—AMPHARTHRANDRIA 61 Sub-Order 2. Podoplea. The boundary between the fore and hind part of the body falls in front of the fifth thoracic segment. The appendages of the fifth thoracic pair in the male are never modified as copulatory organs. TRIBE I. AMPHARTHRANDRIA. The first antennae in the male differ greatly from those in the female, being often geniculated and acting as prehensile organs. Fic. 28.—Luterpe acutifrons, 2, Fic. 29.—First antenna of x 70. Abd.1, 1st abdominal Euterpe acutifrons, 6. segment; 7h.5, 5th thoracic (After Giesbrecht. ) segment. (After Giesbrecht. ) Fams. 1-2. Cyclopidae and Harpacticidae, and other allied families, are purely free-living forms; they are not usually pelagic in habit, but prefer creeping among algae in the httoral zone or on the sea-bottom, or especially in tidal pools. Some genera are, nevertheless, pelagic ; e.g. Oithona among Cyclopidae ; Setella, Clytemnestra, and Aegisthus among Harpacticidae. The sketch (Fig. 28) of Huterpe acutifrons 9 , a species widely 62 CRUSTACEA——COPEPODA CHAP. distributed in the Mediterranean and northern seas, exhibits the structure of a typical Harpacticid, while Fig. 29 shows the form of the first antenna in the male. Several fresh-water representatives of these free-living families occur. The genus Cyclops (Cyclopidae) is exclusively fresh-water, while many Harpacticidae go up into brackish waters: for example on the Norfolk Broads, Mr. Robert Gurney has taken Tachidius brevicornis, Miiller, and 7. littoralis, Poppe; Ophio- camptus brevipes, Sars; Mesochra lilljeborgi, Boeck; Laophonte littorale, T. and A. Scott; JZ. mohammed, Blanchard and Richard; and Dactylopus tisboides, Claus. Schmeil? gives the following scheme for identifying the fresh-water Cyclopidae and MHarpacticidae (see diagnosis of Centropagidae on p. 59) :— Fam. 1. Cyclopidae.—The cephalothorax is clearly separated from the abdomen. The first antennae of the female when bent back do not stretch beyond the cephalothorax ; in the male both of them are clasping organs. The second antennae are without an exopodite. The fifth pair of limbs are rudimentary, there is no heart, and the female carries two egg-sacs. Cyclops—Numerous species, split up according to segmentation of rudimentary fifth pair of legs, number of joints in antennae, ete. Fam. 2. Harpacticidae.—The cephalothorax is not clearly separated from the abdomen. The first antennae are short in both sexes, both being clasping organs in the male. The second antennae have a rudimentary exopodite. The fifth pair of limbs are rudimentary and plate-shaped; a heart is absent, and the ege-sacs of the female may be one or two in number. 1. Ophiocamptus (Moraria).—Body worm-shaped ; first antennae of female 7-jointed, rostrum forming a broad plate. Body not worm-shaped ; first antennae of female 8-jointed, rostrum short and sharp. (“) Endopodites of all thoracic limbs 3-jointed. The first antennae in female distinctly bent after the second joint. Nitocra. (b) Endopodite of at least the fourth limb 2-jointed ; first antennae in female not bent. Canthocamptus. 3. Ectinosoma.—Body as in 2, but first antennae are very short, and the maxillipede does not carry a terminal hooked seta as in 1 and 2. bo 1 Loc. cit. p. 59. III PODOPLEA——AMPHARTHRANDRIA 63 Fam. 3. Peltiidae.'— This is an interesting family, allied to the Harpacticidae, and includes species with flattened bodies somewhat resembling Isopods, and a similar habit of rolling themselves up into balls. No parasitic forms are known, though Sunaristes paguri on the French and Scottish coasts is said to live commensally with hermit-crabs. We have now enumerated the chief families of free-living Copepods; the rest are either true parasites or else spend a part of their lives as such. A number of the semiparasitic and parasitic Copepods can be placed in the tribe Ampharthrandria owing to the characters of their antennae; but it must be remembered that many parasitic forms have given up using the antennae as clasping organs; however, the sexual differences in the antennae, and the fact that many of the species which have lost the prehensile antennae in the male have near relations which preserve it, enable us to proceed with some certainty. The adoption of this classification necessitates our separating many families which superficially may seem to resemble one another, e.g. the semiparasitic families Lichomolgidae and Ascidi- colidae, and the Dichelestiidae from the other fish-parasites; it also necessitates our treating the presence of a sucking mouth as of secondary importance. This characteristic must certainly, how- ever, have been acquired more than once in the history of the Copepods, for instance in the Asterocheridae and in the fish- parasites, while it sometimes happens that genera belonging to a typically Siphonostomatous group possess a gnathostome, or biting mouth, ey. Ratania among the Asterocheridae. Again, it is impossible even if we use the character of the mouth as a criterion to place together all the true parasites on fishes in one natural group, because the Bomolochidae and Chondracanthidae, which are otherwise closely similar to the rest of the fish-para- sites, possess no siphon. It seems plain, therefore, that the parasitic habit has been acquired several times separately by diverging stocks of free-swimming Copepods, and that it has resulted in the formation of convergent structures. Fam. 4. Monstrillidae.—These are closely related to the Harpacticidae. The members of this curious family are parasitic during larval life and actively free-swimming when adult. There 1 Claus, Copepodenstudien, 1. Heft, Vienna, 1889. 2 Malaquin, Arch. Zool. Exp. (3), ix., 1901, p. 81. 64 CRUSTACEA—COPEPODA CHAP. are three genera, Monstrilla, Haemocera, and Thaumaleus, The best known type is Haemocera danae (often described as Monstrilla danae). In the adult state (Fig. 30) there are no mouth-parts ; the mouth is exceedingly small and leads into a very small stomach, which ends blindly, while the whole body contains reserve food- material in the form of brown oil-drops. The sole appendages on the head are the first an- tennae; but on the thorax biramous feet are present by means of which the animal can swim with great rapidity. This anomalous organisation receives an explanation from the remarkable development through which the larva passes. The larva is liberated Fig. 30.—Haemocera danae, x 40. A, Side Fic. 31. — Free-swimming Nauplius view ? ; B, ventral view g. CETy Fig. 32.—Later stages in the development of Haemocera danae. Abd, Abdomen ; Ant.1, Ant.2, 1st and 2nd antennae ; ch, chitinous investment ; e, eye ; “ef, ecto- derm ; Hn, endoderm ; Mes, mesoderm ; Mes d& en, mesoderm and endoderm ; R, rostrum ; St, mouth and stomach ; 7h, thoracic appendages. (After Malaquin.) cells, representing ectoderm and endo-mesoderm, surrounded by a chitinous membrane (Fig. 32, A). Arrived in the ventral blood- vessel it begins to grow, and the first organ formed is a pair of fleshy outgrowths representing the second antennae (Fig. 32, B), which act as a nutrient organ intermediary between host and VOL. IV Yr 66 CRUSTACEA—COPEPODA CHAP, parasite. The adult organs now begin to be differentiated, as shown in Fig. 32, C, from the undifferentiated cellular elements of the Nauplius, the future adult organism being enclosed in a spiny coat from which it escapes. At this stage ib occupies a large part of its host’s body, lying in the distended ventral blood- vessel, and it escapes to the outside world by rupturing the body- wall of the worm, leaving behind it the second antennae, which have performed their function as a kind of placenta. Malaquin, to whom we owe this account, makes the remarkable statement that if two or three Monstrillid Naupli develop together in the same host they are always males, if only one it may be either male or female. The only parallel to this extraordinary life- history 1s found in the Rhizocephala (see pp. 96-99). Fam. 5. Ascidicolidae.'—Although the members of this family, which live semiparasitically in the branchial sac or the gut of Ascidians, betray their Am- pharthrandrian nature by the sexual differences of their first antennae, only two genera, WVoto- delphys and Agnathaner, possess true prehensile antennae. Ac- cording as the parasitism is more or less complete, the buccal appendages either retain their Fra. 33.—Side view of Doropygus pulec, Masticatory structure or else brood- pouch; h.1, Ast thoracic of fixation. In WNotodelphys both Pe cana ae thoracle Se sexes can swim actively and retain normal mouth-parts; they live parasitically, or perhaps commensally, in the branchial cavities of Simple or Compound Ascidians, feeding on the particles swept into the respiratory chamber of the host. They leave their host at will in search of a new home, and are frequently taken in the plankton. Doropygus (Fig. 33), a genus widely distributed in the North Sea and Mediterranean, also inhabiting the branchial sac of Ascidians, is more completely parasitic, and the female cannot swim actively. Forms still more degraded by a parasitic habit are Ascidicola rosea (especially abundant in the stomach of 1 Canu, Trav. Inst. Zool. Litte. vi., 1892. III PODOPLEA—-AMPHARTHRANDRIA 67 Ascidiella scabra at Concarneau), in which the female has lost its segmentation, the mouth-parts and thoracic legs being purely prehensile, and various species of Hnterocola, parasitic in the stomach of Compound Ascidians, in which the female is a mere sac incapable of free motion, while the male preserves its swim- ming powers and a general Cyclops-form (Fig. 34). We Fig. 34.—Hnterocola fulgens. A, Ventral view Cie ohec 235 + By asides view! iol 16, oc LOG. F « ; “af Abd.1, 1st abdominal segment ; Ant.1, Ant.2, 1G. 3 : Asteroc veres Bees g, Ist and 2nd antennae; c.m, gland-cells; 2, with egg-sacs, x 5/7. (After elit , ventral nerve-cord ; og, oviducal gland ; ov, ovary ; Giesbrecht.) po, vagina; Th.7, [st thoracic appendage ; Th. 4, Th.d, 4th and 5th thoracic segments. (After Canu. ) have here the first instance of the remarkable parallelism between the degree of parasitism and the degree of sexual dimorphism, a parallelism which holds with great regularity among the Cope- poda, and can be also extended to other classes of parasitic animals. Fam. 6. Asterocheridae.'—These forms retain the power of swimming actively, and are very little modified in outward appearance by their parasitic mode of life (Fig. 35), though they 1 Giesbrecht, Fauna and Flora G. v. Neapel, Monogr. 25, 1899. 68 CRUSTACEA——-COPEPODA CHAP. possess a true siphon in which the styliform mandibles work. The siphon is formed by the upper and lower lips, which are produced into a tube with three longitudinal ridges; in the outer grooves are the mandibles, while the inner groove forms the sucking siphon (see transverse section, Fig. 36). In Ratania, however, there is no siphon. ‘The first antennae possess a great number of joints, and may be geniculated in the male (Cancerilla). The members of this family live as ectoparasites on various species of Echinoderms, Sponges, and As- cidians, but they frequently change their hosts, and it appears that one and the same species may indifferently suck the juices of Fra, 36.— Diagrammatic very various animals, and evén of Algae. transverse section through the distal part Cancerilla tubulata, however, appears to live liege nape aaa. only on the Brittle Starfish, Amphiura tum (Asterocheridae). squamata. aE ee Fam. 7. Dichelestiidae.—The males and females are similarly parasitic, and the body in both is highly deformed, the segmentation being suppressed and the thoracic limbs being produced into formless fleshy lobes ; they are placed among the Ampharthrandria owing to sexual differences in the form of the first antennae. There is a well- developed siphon in which the mandibular stylets work, except in Lamproglena, parasitic on the gills of Cyprinoid fishes; the succeeding mouth-parts are prehensile. The majority of the species are parasitic on the gills of various fish (Dichelestium on the Sturgeon, Lernanthropus’ on Labrax lupus, Serranus scriba, etc.), but Steuer” has recently described a Dichelestiid (Aytilicola) from the gut of Mytilus galloprovincialis off Trieste. This animal and ZLernanthropus are unique among Crustacea through the possession of a completely closed blood- vascular system which contains a red fluid; the older observers believed this fluid to contain haemoglobin, but Steuer, as the result of careful analysis, denies this. The parasite on the gills of the Lobster, Nicothoe astaci, possibly belongs here. The inclusion of Wicothoe and the Dichelestiidae among the Ampharthrandria rests on a somewhat slender basis; this basis is afforded by the fact that none of the parasitic Isokerandria have more than seven joints in the’ first antennae, whereas 1 Arb. Zool. Inst. Wien, ii. 1879, p- 268. 2" Tbtd. xv, 1905; sped I PODOPLEA—ISOKERANDRIA 69 Nicothoe and some of the Dichelestiidae’ have more numerous joints. In most of the Dichelestiidae, however, the number of joints is less than seven and practically equal in the two sexes. TRIBE Il ISOKERANDRIA. The first antennae are short, similar in the two sexes, and are never used by the male as clasping organs. ‘This function may be subserved by the second maxillae. FAMS. ONCAEIDAE, CORYCAEIDAE, LICHOMOLGIDAE, ERGA- SILIDAE, BOMOLOCHIDAE, CHONDRACANTHIDAE, PHILICHTHYIDAE, NEREICOLIDAE, HERSILIIDAE, CALIGIDAE, LERNAEIDAE, LERNAE- OPODIDAE, CHONIOSTOMATIDAE. The families Oncaeidae and Corycaeidae contain pelagic forms of flattened shape and great swimming powers, but the structure of the mouth-parts in the Corycaeidae points to a semi-parasitic habit. Fam. 1. Oncaeidae.—This family, including the genera Oncaea, Pachysoma, ete., does not possess the elaborate eyes of the next family, nor is the sexual dimorphism so marked. Fam. 2. Corycaeidae.—These are distinguished from the Oncaeidae, not only by their greater beauty, but also by the possession of very elaborate eyes, which are furnished with two lenses, one at each end of a fairly long tube. The females of Sapphirina are occasionally found in the branchial cavity of Salps, and their alimentary canal never contains solid particles, but is filled with a fluid substance perhaps derived by suction from their prey. /S. opalina may occur in large shoals, when the wonderful iridescent blue colour of the males makes the water sparkle as it were with a sort of diurnal phosphorescence. The animal, however, despite the opinion of the older observers, 1s not truly phosphorescent. It may be that the ornamental nature of some of the males is correlated with the presence of the curious visual organs, which are on the whole better de- veloped in the females than in the males. As in so many pelagic Copepods, the body and limbs may bear plumed setae of great elaboration and beautiful colour, eg. Copilia vitrea (Fig. 37). We now pass on to the rest of the parasitic Copepods,” which 1 Heller, Reise der Novara, vol. iii., 1868. ? For fish-parasites in British waters consult Scott, Fishery Board for Scotland, Scientific Investigations, xix., 1900 et seq. fod 7O CRUSTACEA—COPEPODA CHAP. probably belong to the tribe Isokerandria, and we meet with the same variety of degrees of parasitism as in the Ampharthrandria, often leading to very similar results. In the first seven families mentioned below there is no Fic. 37.—Copilia vitrea (Corycaeidae), 9, x 20. (After Giesbrecht. ) siphon. The Lichomolgidae and Ergasilidae have not much departed from the free-living forms just considered, retaining their segmentation, though in the Ergasilidae the body may be somewhat distorted (Fig. 39). In both families the thoracic swimming feet are of normal constitution. Fam. 3. Lichomolgidae.'—These are semi-parasitic in a number of animals living on the sea-bottom, such as Actinians, ' Cann, oc. cit. p. 66. Ill PODOPLEA—ISOKERANDRIA JX Echinoderms, Annelids, Molluscs, and Tunicates. Lichomolgus agilis (Fig. 38) occurs in the North Sea, Atlantic, and Mediter- ranean, on the gills of large species of the Nudibranch, Doris, while LZ. albeus is found in the peribranchial cavity and cloaca of various Ascidians. Sabel- liphilus may infect the gills of Annelids such as Sabella, and is common at Liverpool. Fam. 4. Ergasilidae. — hersites (Fig. 39) is parasitic on the gills of various fishes, eg. 7. gasteroster, which is common on (Gasterosteus aculeatus on the French and North Sea coasts, and may even be found on specimens of the fish that have run up the River Forth into fresh water. The animal Ftc. 38. — Lichomolgus agilis, “x10. Abd.7, 1st abdominal possesses claw-like second antennae by ecuients oni cophalothonax: which it clings to its host. HE USE DAO EIEIO Soe see : Th.5, 5th thoracic appendage. Similarly characterised by the (After Camu.) t Fia. 39.—Thersites gasterostet. A, OF xX Ol Bade 20Lg edb. 1 & 2, Fused Ist and 2nd ab- dominal segments; Ant. 1, Ant. 2, Ist and 2nd antennae ; ¢.s, egg- sac; Th, thoracic appendages. (After Gerstaecker. ) oar acer RUG BSS absence of a siphon are three other families of fish-parasites, the Bomolochidae, Chondracanthidae, and Philichthyidae. Fam. 5. Bomolochidae.— Pomolochus (Fig. 40), parasitic on the skin of the Sole (So/ew) and in the nostrils of Cod (Gadus), is held to be related to the Ergasilidae. The first thoracic limb is remarkably modified, Were it not for the absence of a siphon, it would be hard to separate this family from the Caligidae. N N RUSTACEA——COPEPODA CHAP. Fam. 6. Chondracanthidae.— These Copepods infest the gills Fic. 40.—Bomolochus, sp. (Bomo- lochidae), x 8. Abd.1, 1st abdo- minal segment; Ant.Z, Ant.2, Ist and 2nd antennae; Mz./, Mzx.2, \st and 2nd maxillae ; Map, maxillipede ; 7h.7, 1st thoracic appendage. (After Gerstaecker. ) and even the mouth of various marine fish, such as the Gurnard, Plaice, Skate, Sole, and many others. VARET The sexual dimorphism is very marked, Ve the female being large, indistinctly segmented, and with irregular paired processes protruding from the sides of the body, giving the animal a mon- Fic. 42.—Dwarf male of Lernen- toma cornuta (Chondracan- thidae), x 10. Ant.1, Ant.2, Ist and 2nd antennae; Th./, Ist thoracic segment. (After Kia. 41.—Chondracanthus zei, 9, x 4. Gerstaecker. ) strous form (Fig. 41) ; while the male (Fig. 42) is very small, has a 11 PODOPLEA—ISOKERANDRIA Z3 completely segmented thorax, and lives clinging on to the female by its prehensile second antennae—Chondracanthus, Lernentoma. Fam. 7. Philichthyidae— These parasites, which are hardly known to occur in British waters,’ are mucus-feeders and infest the skin of Teleosts, e.g. the Sole; often taking up a position in the lateral line or in a slime canal. They show a similar sexual dimorphism to the foregoing family, the adult female being extraordinarily drawn out into finger-like processes (¢.g. Philich- thys)* or else long, slender, and Nematode -like, with much reduced appendages (Lernaeascus), while the male retains a more normal structure. As in all the foregoing forms there is no siphon. We now return to two semi-parasitic families, Fam. 8, Nereico- lidae, and Fam. 9, Hersiliidae, in which there is certainly no well-developed siphon, but the upper and under lips protrude, forming a hollow between them in which the mouth-parts work. Both families are ectoparasites which frequently leave their hosts, and they retain their segmentation and powers of swim- ming. Perhaps the best-known form is the Hersiliid, Giardella callianassae, Which lives in the adult state in the galleries ex- cavated in the sand by Callianassa subterranea, gaining. its nourishment as an ectoparasite on the Decapod. The larvae are pelagic, and are said by Thomson® to occur in Liverpool Bay. List* describes Gastrodelphys, a parasite of doubtful position, from the gills of tubicolous worms, such as Myaicola and Sabella, which possesses a perfectly siphonostomatous mouth. The remaining families to be dealt with are those containing all the fish-parasites which possess a true siphonostome, as well as the siphonostomatous family Choniostomatidae, which is para- sitic on other Crustacea. In all these forms the mouth is pro- longed into a tube in which the styliform mandibles work. Fam. 10. Caligidae——LEctoparasites on fish, lodging most frequently in the gill-chamber. In most of the genera the segmentation and power of swimming are retained in both sexes, the sexual dimorphism not being very well marked, though the males are smaller than the females, and were in some cases originally described as belonging to a special genus Nogagus. ' The Cambridge Museum possesses two specimens of Philichthys xiphiae, from the frontal bones of a Swordfish (Xiphias gladius) taken off Lowestoft in 1892. * Claus, Arb. Zool. Inst. Wien, vii., 1888, p. 281. 3 Proc. Biol. Soc. Liverpool, i., 1887. 4 Zeitschr. wiss. Zool. xlix., 1890, p. 71. 74 CRUSTACEA—COPEPODA cHap. The females carry two long egg-sacs; the general structure may be made out from the ventral view of Caligus nanus (Fig. 43). Some of the Caligidae are distinguished by the terga of the thoracic segments being expanded to form large chitinous elytra, e.g. Cecrops, found parasitic on the gills of the Tunny and on the Sun-fish (Orthagoriscus mola). Caligus rapax is parasitic on the skin and in the gills of Sea-Trout, Pollan, ete.; and C. lacustris is common in fresh-water lakes and streams on Pike and Carp. we WAN KX Fic. 43.—Caligus nanus, x 10. Abd.1, Fic. 44.—Lernaea branchialis from 1st abdominal segment ; Ant./, Ant. 2, the Haddock, 9, x 1. Ceph, Ist and 2nd antennae ; Max.1, Mza.2, cephalothorax ; és, egg - sacs. Ist and 2nd maxillae ; Map, maxilli- (After Scott. ) pede ; s, siphon; 7h.7, Th.d 1st and 5th thoracic appendages. (After Ger- staecker. ) Fam. 11. Lernaeidae——These parasites burrow with their heads deep into the skin, or even into the blood-vessels or body- cavity, of various marine fish. The body of the adult female Lernaea is extraordinarily deformed, consisting of a mere shape- less sac with irregular branched processes on the head, and two egg-sacs attached behind (Fig. 44). Pennella sagitta’ bores so deeply into the flesh of its host, Chironectes marmoratus, that only the egg-sacs and some remarkable branchial processes attached to its abdomen protrude outside the host to the 1 > “| 5 s 7 . . The genus Pennella also includes parasites on the whales Hyperoodon and Lalaenoptera. mI PODOPLEA—ISOKERANDRIA 7% exterior. Peroderma cylindricum bores similarly into the flesh of the Sardine, and where it is common, inflicts considerable damage. The males of these curious animals are of more normal structure (Fig. 45). Claus’ states that fertilisation takes place when both sexes are free-swimming, and of a more or less similar structure, and that subsequently the female Fie. 45.—Lernaea branchialis, Fic. 46.—Achtheres percarum. A, 9, x 4; B, G5 & LOD Ant. 1, AnéZs Ist 6, x 4. Ant.2, 2nd antenna; g, stomach ; and 2nd antennae ; Br, brain; Mz.2, 2nd maxilla; Map, maxillipede; ov, e, eye ; g, stomach ; ¢, testis ; ovary ; ovd, oviduct. (After Gerstaecker. ) vd, vas deferens; ves. sem, vesicula seminalis. (After Claus.) becomes fixed to her host and degenerates into the shapeless mass shown in Fig. 44. Fam. 12. Lernaeopodidae.—This family may be illustrated by the common gill-parasite of Perch and Trout, known as Achtheres percarum. The female (Fig. 46), which is much larger than the male, and is not clearly segmented, is attached to the host by means of the maxillipedes, which are fused distally into a pad armed with chitinous hooks. In the male the maxillipedes 1 Claus, Schriften d. Gesellsch. Marburg. Suppl. 1868. 76 CRUSTACEA—COPEPODA CHAP. are prehensile, but are not so fused. Besides Achtheres there are other fresh-water forms, e.g. Lernaeopoda salmonea on Salmon, and a number of marine genera. It appears that the larvae fix themselves to their hosts by means of a long glandular thread, which proceeds from the middle of the forehead. Fam. 13. Choniostomatidae.°—The members of this family are all parasitic on other Crustacea. | The majority live parasiti- cally in the marsupial pouches of female Amphipods, Isopods, Mysidae, and Cumacea, e.g. Sphaeronella and Stenochotheres in the marsupiaof Gammarids ; but Chonio- stoma occurs in the branchial cavity of Hippolyte, Homoeoscelis is common in the branchial cavity of Diastylis S and Lphinoe, and Aspidoecia on the outside of the body of the Mysid Erythrops. The males and females live together in the same marsupium, but the adult males retain the power of roving about, and do not feed so much as the females, though their mouth - parts are similarly con- structed (Fig. 47). Representatives occur all over the world, but the majority of species known at pre- Fic. 47.—Ventral view of Stenocho- gent are from the North Sea, the theres egregius (Choniostomatidae), : $. A, A’, Istand2ndantennae; Most abundant being Stenochotheres a Dae at itera egregius, parasitic on the Gammarid sen.) ; Metopa bruzelit, Goés. The male bears a median glandu- lar thread on the forehead by which it attaches itself to the females or to the host. Hansen considers that the family is most closely allied to the Lernaeopodidae. BRANCH II. BRANCHIURA. Fam. Argulidae.*-—We have yet to mention this group of fish-parasites, related to the Copepoda, but occupying an isolated 1 Claus, Zeitschr. wiss. Zool. xi., 1861, p. 287. * Hansen, ‘‘The Choniostomatidae,” Copenhagen. * Claus, Zeitschr. wiss. Zool. xxv., 1875, p. 217. UI BRANCHIURA—ARGULIDAE I Gf position. They are ectoparasites upon various species of fish, Argulus foliaceus being common in the fresh waters of Europe, infesting the branchial chamber or the skin of fresh-water fish, but being frequently taken swimming freely in the water. tom MG wl SE VG Fic, 48.—Argulus foliaceus, young 6, x 15. a, a, First and second antennae ; ab, abdomen, #, compound eye ; J, liver ; m, mandibles and first maxillae ; mx, second maxilla (the median eye is seen between the two second maxillae) ; map, maxilli- pede; s.g, shell-gland; sp, spine; ¢, testis; 1, 4, first and fourth swimming appendages. (After Claus.) Both males and females can swim with great agility, and they leave their hosts regularly at the breeding season in spring and autumn ; fertilisation is internal, and the female deposits the eggs on stones and other objects. After leaving its host, an Argulus, if it cannot find a fish of the same species, can live on almost any other species, and may even attack Frog tadpoles ; while the kinds that infest migratory fish can change with their 78 CRUSTACEA—COPEPODA CHAP. III hosts from salt to fresh water, or the reverse. America appears to be the home of the Argulidae.* The structure of an Argulid is exhibited in Fig. 48. In front of the siphon, within which the styliform mandibles and first maxillae work, there is a poison-spine (sp); the appendages which correspond to the second maxillae (ma) are modified into sucking discs, but in the genus Dolops they terminate in normal claws. The next pair of appendages, usually spoken of as maxilli- pedes (map), are clasping organs, and behind follow four pairs of thoracic swimming feet (1-4). The body is foliaceous, and they always apply themselves to their hosts with the long axis pointing forwards and parallel to that of the host, while on various parts of the under surface of the body are spines pointing backward which prevent the parasite being brushed off by the passage of the host through the water. These animals, alone among the Copepoda, possess compound eyes. A short sketch has now been given of the variations in Copepod organisation, but we cannot leave the subject without pointing out the rich field which still remains for the morphologist, especially in determining the true relationships of the parasitic families. 1 C, B. Wilson, Proc. U.S. Nat. Museum, xxv., 1902, p. 635, CHARTER Ly. CRUSTACEA (CONTINUED) : CIRRIPEDIA——PHENOMENA OF GROWTH AND SEX—OSTRACODA Order III. Cirripedia. THE Cirripedes are medium-sized Crustacea, with the body consist- ing of few segments, and enveloped in a mantle formed as a fold of the external integument, which may be strongly protected by ealcified plates. The abdomen is greatly reduced. The larva, after hatching out as a Nauplius, and passing through a Cypris stage, when it resembles an Ostracod, fixes itself to a foreign object by means of the first antennae, and becomes a pupa, which after profound changes gives rise to the adult. All the Cirripedes, when adult, live either a fixed or parasitic existence, and as so frequently happens with animals of this kind, they have departed widely from the ordinary structure of the class to which they belong. Their anomalous appearance and the mystery surrounding their propagation gave rise, probably, to the old legend that the Barnacles (Lepadidae), which live attached to pieces of floating timber hatched out into Barnacle geese’; and even so late as 1678, in the Royal 1 Max Miiller (Science of Language, 2nd series, p. 534) gives references to a number of old authors who vouch for the truth of this legend, going back as far as Giraldus Cambrensis in the twelfth century. The legend appears to be of Scotch or Irish origin. Giraldus complains of the clergy in Ireland eating Barnacle geese at the time of fasting under the pretext that they are not flesh, but born of fish living in the sea. The form of the legend varies, certain authors alleging that the geese are produced from the fruits of a tree which drop into the water, others that they grow in shells (Barnacles) attached to floating logs. Aldrovandus (De Avibus, T. iii., 1603, p. 174) ingeniously combines both versions in a woodcut representing undoubted Barnacles growing on a tree with luxuriant foliage at the water's edge, below which a number of liberated geese are swimming. Miiller ascribes an etymo- 79 80 CRUSTACEA—CIRRIPEDIA CHAP. Society’s Zransactions, Sir Robert Moray describes what he takes to be little birds enclosed in Barnacle shells, washed ashore on the coast of Scotland: “The little Bill like that of a Goose, the Eyes marked, the Head, Neck, Breast, Wings, Tail, and Feet formed, the Feathers everywhere perfectly shaped and blackish coloured, and the Feet like those of other Water-fowl, to my best remembrance.” Cuvier in his classification of the animal kingdom included them in the Mollusca; and it was not until 1830 that J. V. Thompson described their larval stages, and showed conclusively that they belonged to the Crustacea. Since the work of this naturalist a number of observers have securely founded our knowledge of the group, but we may especially mention the epoch-making works of Darwin,’ Hoek,’ and latterly of Gruvel.* The young Cirripede is hatched out from the maternal mantle-cavity as a free-swimming Nauplius, a larval form common to most of the Entomostraca and to some Malacostraca ; the Cirripede Nauphus (Fig. 49) is characterised by the presence of well-developed frontal horns, and usually by the long spiny processes which spring from various parts of the body. As an introduction to the study of the group, it will be well to follow the transformations of this larva in Zepas up to the period when it begins its sessile existence. The liberated Nauplii swim freely near the surface of the sea, and remaining in this condition for several days are dispersed widely from their birthplace ; they are then transformed by the process of moulting into the second larval stage, known as the Cypris (Fig. 50), from its resemblance to a bivalve Ostracod. The Cypris larva continues to swim about by means of the six pairs of biramous thoracic legs until it finds a suitable place on which to fix; in the case of Lepas fixation usually takes place on loose floating logs; the Cypris fixes itself by means of the first antennae, at the bases of which a large cement-gland secretes an adhesive substance. The biramous swimming legs are cast off, and six pairs of biramous cirri characteristic of the adult take their logical origin to the legend, the Barnacle goose (deriv. Hibernicula, bernicula=Ivish goose) being confounded with pernacula, bernacula, a little shell. * “A Monograph of the Cirripedia,” vols. i. and ii., Ray Society, 1851, 1853. * **Rep. on the Cirripedia, H.M.S. ‘Challenger,’ ” vols. viii. and x., 1883. * “Monographie des Cirrhipédes,” Paris, 1905, in which will be found full references to literature. Iv METAMORPHOSIS SI place; at this stage the body has the appearance shown in Fig. 51. The region of the head at the base of the antennae now becomes greatly swollen and elongated to form the peduncle i Fie. 49.—Nauplius larva of Lepas fascicularis, x 12. Aj, As, 1st and 2nd antennae ; b, brain; , eye; H, fronto-lateral horn ; MW, mandible; S, stomach. (After Groom.) or stalk of the adult; the larval bivalve carapace is cast off and on the external surface of the mantle the calcifications begin which will give rise to the exoskeletal plates of the adult. This region is known as the “ capitulum ” of the adult, as opposed to the “peduncle.” The young Cirripede is now known as a pupa, and _from this stage the adult form is reached by a gradual transition. VOL. IV G 82 CRUSTACEA—CIRRIPEDIA CHAP: The body of the adult Zepas is retracted into the mantle, Fic. 50.—Cypris-stage in the development of Lepas australis, x 15. A, Peduncle ; A.M, adductor muscle ; ©, caecum of oesophagus ; C.g, cement-glands ; Cr, cirri (thoracic appendages); H, compound eye; H', simple eye; G, ventral ganglia ; T, intestine; 7, mouth; J.C, mantle-cavity; O, ovary; S, stomach. (After Hoek. ) and les free in the Fic. 51.—Pupa of Lepas pectinata, x 8. A, An-* tenna; C, carina; JM, adductor muscle; SS, scutum ; 7’, tergum. (After Gruvel.) mantle-cavity, but is continuous anteriorly with the tissues of the peduncle, into which the mantle does not extend. The thorax, with its six pairs of legs, can be protruded from the mantle-cavity through the slit- like opening which separates the two valves of the mantle along the ventral middle line ; and when the animal is feeding, the thoracic legs are so protruded, and by their concerted waving action they drive the food-particles in the water along the channel between them, until the particles reach the oral cone, where they are masticated by the mandibles and two pairs of maxillae, and so passed into the alimentary canal. When the animal is disturbed it rapidly retracts its limbs, the valves of the mantle are closed by ineans of a strong adductor muscle in the head, and the animal is protected from all external influences. In the acorn-barnacles (Operculatay, IV ANATOMY 8 3 which live in great numbers attached to rocks and other objects between tide-marks, the body is constructed on a similar plan, save that there is no stalk, and the body is completely enclosed in a hard caleareous box formed from the mantle, which, when the valves are closed, as they always are during low tide, completely protect the animal inside from desiccation or danger of any kind. Besides the cement-glands situated in the peduncle, we can distinguish the generative organs, consisting of a pair of ovaries and testes, the majority of Cirripedes being hermaphrodite. The testes open at the end of an elongated median penis behind the thoracic limbs, Fic. 52.—A, Dwarf male of Scalpellum vulgare, x 27; B, diagram of Stalked rnacle. «a, Pedunele; a@/, alimentary canal; }, brain ; c, carina; e, r ins of Barnacl , Peduncle ; al, al t We (ays to ; ¢, carina; e, remains of Nauplius eye; g/, cement-gland ; mm, mantle-cavity ; 0, its opening; ov, ovary ; Naupl Vers gs t-gland ; tl t ts opening ovary Ps penis ; s, scutum ; ¢, testis ; tm, tergum, seen in A as the shaded body above the reference-line of e and to the right of the carina, on the left of the figure. while the ovaries, situated in the peduncle, have paired openings into the mantle-cavity on either side of the head. 7, tergum., (After Darwin.) Fria. 59.— lbla cumingii, dwarf male, x 32. A, Antennae ; b, part of male imbedded in the female, to which the torn membrane J belongs ; Ii, eye; Th, thoracic ap- pendages or cirri, (After Darwin.) female’s mantle, inside IV PEDUNCULATA—OPERCULATA 89 which they live; they exhibit a degenerate structure, but still retain two pairs of cirri. The large individuals of 7. guadrivalvis, on the other hand, are hermaphrodites, but they harbour within their mantles minute complemental males similar to those of I. cumingit, though they are rather larger. Fam. 4. Anaspidae.—This includes the remaining pedun- culate genera, characterised by the fleshy nature of the mantle and peduncle, which are both entirely devoid of eal- cifications. The species of Alepas live upon Echinoderms and various other animals; Chaetolepas upon Sertularia, and Gymnolepas upon Medusae. Anelasma squalicola is an interesting form, living parasitically upon the Elasmobranch fishes, Se/ache maxima and Spinax niger in the North Sea. The peduncle is deeply buried in the flesh of the host, so that only a portion of the dark blue capitulum protrudes to the surface. From the whole surface of the peduncle a system of branching processes is given off, which ramify far into the tissues of the fish, and communicate inside the peduncle with the lacunar tissue, which is packed round all the organs of the Cirripede. There can be small doubt that the Ane/asma derives its nutriment parasitically through this root-system, since the cirri are mere fleshy lobes un- adapted to securing food, and the alimentary canal is always empty. This animal has a sug- gestive bearing on the Rhizo- cephala, which, as will be shown, derive their nutriment from a system of roots penetrating the host and growing out from what corresponds morphologically to the peduncle. Sub-Order 2. Operculata. Fic. 60.—Diagram of the shell of an Operculate Cirripede. @ * Ala,” or The “ acorn-barnacles ” appear overlapped portion of a ‘ compart- = 5 5 p rai s. basis: ©. carina: GOL, iter im ceolosical time’ that the © ett 3%: basis), G carina, C.2 5 5 carino-lateral ; Z, lateral; &, ros- earher stalked forms. Verruca and trum; 7, “radius,” or overlapping : - portion of a compartment; R.L Chthamalus are found in the Chalk, ee lab ral, (After Darvin} os and survive down to the present day, but Lalanus does not occur until middle Tertiary times. Representatives of the last-named genus are familiar to every one, 90 CRUSTACEA—CIRRIPEDIA CHAP. a as the hard sharp objects which cover rocks and piles near high- water mark on every sea-coast. If we examine the hard skeleton of one of these animals, we find that, unlike the Pedunculata, they possess no stalk, the capitulum being fused on to the surface of attachment by a broad basal disc. Typically, there may be considered to be eight skeletal pieces forming the outer ring which invests the soft parts of the animal, an unpaired rostrum and carina, and laterally a pair of rostro - lateral, lateral, and carino-lateral “compartinents,” as shown in Figs. 60, 63. The skeletal ring 1s roofed over by a pair of terga at the carinal end and a pair of scuta at the rostral end; these four plates make up the operculum by which the animal can shut itself Fic. 61.—Balanus tintinnabulum, with the right half completely up im 1ts shell, of the shell and of the operculum removed, seen oy between the valves of from the right side. A, Antennae, the size of 5 : : which is exaggerated ; A.M, adductor muscle ; which it can protrude 1ts B, basis ; C, carina ; Cr, cirri or thoracic appen- ]jmbs for obtaining food dages ; D, oviduct; G, ovary ; Z, lateral com- ee - z ; partment ; Z6, labrum or upper-lip; I/, MM, The relation of the depressor muscles of secutum and tergum; ILC, ayia j , 7 mantle-cavity ; O, orifice of excretory organ ; animal ; ue ae shell. is O.M, opercular membrane; R, rostrum; SS, shown in Fig. 61... The scutum ; Sf, region of stomach; 7, tergum. G 7 5 (Agen eee Da Veet shell in the Operculata is not merely secreted as a dead structure on the external surface of the epidermis, but repre- Fic. 62.—Diagrammatic section of the growing shell of Ba/- anus porcatus. C, Canals ; Ct, cuticle ; H, hypodermis (=epidermis) ; H’, part of shell secreted by the hypo- dermis ; Hl, hypodermal lamina; J/, part of shell secreted by the mantle. (After Gruvel.) sents a living calciferous tissue interpenetrated by living laminae IV FAMILIES OF OPERCULATA OI (Fig. 62, H1) derived partly from the external hypodermis and partly from the lning of the mantle. The hard parts of the shell usually also contain spaces and canals (C). The various forms of Acorn-barnacle may be classified accord- ing to the number of pieces that go to make eae Ue ore =~ up the skeleton ; thus Bee = ( = starting with the typi- | ( ) ) cal number eight (Fig. 2 63, A), we find that ad Ne in various degrees a R R fae Ge fusion between neigh- s B C Picea ge linn 1 Sh Diners ol Gy of Oovranis 8 Oa taken place In _the (Hexameridae) 5 C, Tetraclita (Tetramenidi2): C, (fitment amas SAE MCca Se ; L, lateral ; R, rostrum ; Fam. 1. Verru- cidae.—The ancient genus Verruca, which is still widely dis- tributed in all seas, and is found fixed upon foreign objects on the sea-bottom at various depths, is interesting on account of the asymmetry of its shell, which bears a different aspect accord- ing to which side one regards it from. This asymmetry is brought about by the skeletal pieces (carina, rostrum, and paired terga and scuta) shifting their positions after fixation has taken place. Fam. 2. Octomeridae.—In this family the eight plates com- posing the shell are separate and unfused (Fig. 63, A). The Inajority of the species come from the Southern hemisphere, e.g. the members of the genera Catophragmus and Octomeris, but Pachylasma giganteum occurs in deep water in the Mediter- ranean, where it has been found fixed upon Millepore corals. Fam. 3. Hexameridae.—This family includes by far the greater number of the Acorn-barnacles, in which only six plates are present, the laterals having fused with the carino-laterals (Fig. 63, B). The very large genus Balanus belongs here, the common £. tintinnabulum of our coasts being found all over the world, and occurring under a number of inconstant varietal forms. Especial interest attaches to certain other genera, from their habit of living parasitically on soft-bodied animals, whose flesh they penetrate. Coronula diadema and Tubicinella trachealis live embedded 92 CRUSTACEA-——CIRRIPEDIA CHAP. in the skin of whales, the shell of the first-named being of a highly complicated structure with hollow triangular compartments into which the mantle is drawn out. Xenobalanus globicipitis lives attached to various Cetacea, and is remarkable for the rudimentary condition of its skeleton, the six plates of which form a mere dise of attachment from which the greatly elongated naked body rises, resembling one of the naked Stalked Barnacles. Fam. 4. Tetrameridae.—In this family only four skeletal plates are present (Fig. 65, C). This family is chiefly confined to tropical seas or those of the Southern hemisphere. The chief genera are Tetraclita and Pyrgoma, found in British seas. Sub-Order 3. Acrothoracica. Gruvel includes in this sub-order four genera (Alcippe, Cryptophialus, Kochlorine, and Lithoglyptes), the species of Fig. 64.—Alcippe lampas. A, 2, x about 10, seen from the right side, with part of the right half of the animal removed; B, dwarf male, x about 30. A.J, adductor muscle; An, antenna; C, lst pair of cirri; Cr, posterior thoracic appendages ; #, eye; G, testis ; M,C, mantle-cavity ; O, ovary; P, penis; Z, penultimate thoracic seg- ment; V. vesicula seminalis. (After Darwin.) which live in cavities excavated in the shells of molluses or in the hard parts of corals. Darwin discovered and described Cryptophialus minutus, and placed it in a sub-order Abdominalia, believing that it was IV ACROTHORACICA ASCOTHORACICA 93 distinguished from all the foregoing Cirripedes by the presence of a well-developed abdomen. Since the discovery of other allied genera, it has been decided that the abdomen is equally reduced in these forms, and that the terminal appendages do not belong to this region, but to the thorax. The sexes are separate. The body of the female (Fig. 64, A) is enclosed in a chitinous mantle, armed with teeth by which the excavation is effected, and is attached to the cavity in the host by means of a horny disc. Upon this disc the dwarf males (B) are found. Alvippe lampas inhabits holes on the inner surface of dead Fusus and Buccinum shells; Cryptophialus minutus the shells of Concholepas peruviana; C. striatus’ the plates of Chiton; Koehlorine hamata the shells of Haliotis; and Lithoglyptes varians shells and corals from the Indian Ocean. Sub-Order 4. Ascothoracica. These are small hermaphrodite animals completely enveloped in a soft mantle, which live attached to and partly buried in various organisms, such as the branching Black Corals (Gerardi). They retain the thoracic appendages in a modified state, and the body is segmented into a number of somites, the last of which probably represents an abdomen. Laura gerardiae, described by Lacaze Duthiers,” is parasitic on the stem of the “ Black Coral,” Gerardia (vol. i. p. 406); it has the shape of a broad bean, the body being entirely enclosed in a soft mantle, with the orifice in the position corresponding to the hilum of a bean. The body lying in the mantle is composed of eleven segments, and is curved into an §S-shape. Its internal anatomy is entirely on the plan of an ordinary Cirripede. Petrarca bathyactidis, G. H. Fowler,? was found in the mesenteric chambers of the coral Bathyactis, dredged by the Challenger from 4000 metres. The body is nearly spherical, and the mantle-opening forms a long slit on the ventral surface. The mantle is soft, but is furnished on the ventral surface with short spines. The antennae, which form the organs of fixation, remain 1 Berndt, Sitzb. Ges. Naturfr. Berlin, 1903, p. 436. * Arch. Zool. Exp. viii., 1880, p. 537. 3 Quart. J. Micr. Sci. xxx., 1890, p. 107. 94 CRUSTACEA—CIRRIPEDIA CHAP. very much in the state characteristic of the Cypris larvae of other Cirripedes, being furnished with two terminal hooks by which attachment is effected. The thoracic appendages, of which there are the normal number six, are reduced flabellate structures, and the abdomen forms an indefinitely segmented lobe of consider- able size. The animal appears to be in an arrested state of development, and so retains some of the characteristics of the Cypris larvae, but it is very doubtful how far these characters can be considered prunitive. Other forms are Dendrogaster astericola on Kchinoderms, and Synagoga mira on the “ Black Coral,” Parantipathes laria, at Naples. Sub-Order 5. Apoda. Darwin described a small hermaphrodite parasite in the mantle chamberof Alepas cor- ‘ nuta from Saint Vin- cent, West Indies, which he named Pro- teolepas bivincta. The body (Fig. 65) is distinctly seg- mented into eleven somites, the last three of which are supposed to belong to the ab- domen ; there are no appendages except the Fic. 65.—Proteolepas bivincta, «x 26. A, Antennae; antennae by which a, 6, Ist and 2nd abdominal segments; O, ovary ; fixation is effected. ea 7, telson ; 1-8, thoracic segments. (After The mouth-parts are of normal constitution. This animal has not been found again since Darwin’s dis- covery, but Hansen" describes a number of peculiar Nauplius larvae taken in the plankton of various regions, which he argues probably belong to members of this group. A wide field of work is offered in attempting to find the adults into which various larvae grow. ' Plankton Expedition, ii. G. d. 1899. IV RHIZOCEPHALA 95 Sub-Order 6. Rhizocephala.' These remarkable animals are Cirripedes which have taken to living parasitically on various kinds of Crustacea; the majority infest species of Decapoda, e.g. Peltogaster on Hermit- Crabs, Sacculina on a number of Brachyura, Sy/on on Shrimps, Lernaeodiscus on Galathea; but one genus, Duplorbis, has been found in the marsupium of the Isopod Calathura brachiata from Greenland. Most of the species are solitary, but a few, e.g. Peltogaster sulcatus, are social. In the adult state the body consists of two portions: a soft bag-like structure, external to the host, carrying the reproductive, nervous, and muscular organs, and attached to some part of the host’s abdomen by means of a chitinous ring; and a system of branching roots inside the host’s body, which spring from the ring of attachment and supply the external body with nourishment. The structure of the external bag-like portion is very simple, and varies only in details, chiefly of symmetry, in the different genera. In Peltogaster, ba which preserves’ the simplest symmetrical arrangement of the organs, a diagrammatic section through the long axis of the body (Fig. 66) shows that it consists of a muscular mantle (m) surround- ing a_ visceral mass, and enclosing a mantle- ov mC Fic. 66.—Nearly median longitudinal section (diagram- matic) of Peltogaster. gn, Brain ; m, mantle ; me, cavity (me) or brood- mantle-cavity ; mes, mesentery ; op, mantle-open- 1 ey Senat al ing ; ov, ovary; ovd, oviduct ; ring, ving of attach- pouch, which stretches ment ; ¢, testis ; vd, vas deferens. everywhere between mantle and visceral mass, except along the surface by which the parasite is attached to its host, where a mesentery (mes) is formed. The ring of attachment is situated in the middle of this mesentery; the. mantle-cavity, which is completely 1 Y. Delage, Arch. Zool. Hap. (2), ii., 1884, p. 417; G. Smith, Fauna u. Flora G. von Neapel, Monogr. 29, 1906. 96 CRUSTACEA—CIRRIPEDIA CHAP. lined externally and internally with chitin, opens anteriorly by means of a circular aperture (op) guarded by a sphincter muscle. The visceral mass is composed chiefly of the two ovaries (ov), which open on either side of the mesentery by means of a pair of oviducts (ovd); the paired testes (/) are small tubes lying posteriorly in the mesentery, and the nervous ganglion (gn) lies in the mesentery between oviducts and mantle-opening. A comparison with the condition of a normal Cirripede (Fig. 67) shows us that the mesenterial surface of the parasite by which it is fixed corresponds to the dorsal surface of an ordinary Pedunculate Cirripede, and that the ring of attachment corresponds with the stalk or peduncle of a Lepas. The root-system passes out through the ring of attachment into the body of the host, and ramifies round the organs of the crab; the roots are covered externally with a thin chitinous investment, Fic. 67.—Diagrammatie median longitudinal section and consist of an epi- through a normal Cirripede. gn, Brain ; op, mantle- opening ; ovd, oviduct ; vd, vas deferens. thelium and an in- ternal mass of branch- ing cells continuous with the lacunar tissue in the visceral mass. The developmental history of the Rhizocephala is one of the most remarkable that embryology has hitherto revealed. It has been most accurately followed in the case of Sacculina. The young are hatched out in great numbers from the maternal mantle-cavity as small Naupli (Fig. 68, A) of a typical Cirripede nature, but without any alimentary canal. They swim near the surface of the sea, and become transformed into Cypris larvae of a typical character (Fig. 68, B). The Cypris larva, after a certain period of free existence, seeks out a crab and fixes itself by means of the hooks on its antennae to a hair on any part of the crab’s body. Various races of Sacculina are known which infest about fifty different species of crabs in various seas; the best known are S. careini parasitic on Carcinus maenas at Plymouth and Iv RHIZOCEPHALA——LIFE-HISTORY 97 Roscott, and S! neglecta on Inachus mauritanicus at Naples. The antenna, by which the Cypris is fixed, penetrates the base of the hair; the appendages are thrown away, and a small mass of undifferentiated cells is passed down the antenna into the body- cavity of the crab. Arrived in the body-cavity it appears that this small mass of cells is carried about in the blood-stream until it reaches the spaces round the intestine in the thorax. Here it becomes applied to the intestine, usually at its upper Fic. 68.—Development of Saceulina neglecta. A, Nauplius stage, x about 70; B, Cypris stage, x about 70. Aj, dy, Ist and 2nd antennae of Nauplius ; Ad, abdomen ; Ant, antenna of Cypris ; /, undifferentiated cells ; 7, frontal horn ; G, glands of Cypris ; H, tendon of Cypris ; M, mandible ; 7, tentacles. part, immediately beneath the stomach of the crab (Fig. 69), and from this point it proceeds to throw out roots in all directions, and as it grows to extend its main bulk, called the central tumour (ct), towards the lower part of the intestine. As the posterior border of the central tumour grows down towards the hind gut, the future organs of the adult Saceulina become differentiated in its substance; the mantle-cavity being excavated and surrounding the rudiment of the visceral mass, while as the central tumour grows downwards it leaves behind it an ever extending system of roots. When the central tumour in process of differentiation has reached the unpaired diverticulum VOL. IV H 98 CRUSTACEA—CIRRIPEDIA CHAP. of the ecrab’s intestine, at the junction between thorax and abdomen, all the adult organs are laid down in miniature, and the whole structure is surrounded by an additional sac formed by invagination known as the perivisceral space (Fig. 70). The young “ Saceulina interna” remains in this position for some time, and being applied to the ventral abdominal tissues: of the crab just at the point where thorax and abdomen join, or Fic. 69.—The mid-gut of Jnachus Fic. 70. Later stage in the develop- mauritanicus with a young Saccu- lina overlying it, x 2. c.t, ‘* Cen- tral tumour” of the parasite ; dai, d.s, inferior and superior diverticula of alimentary canal of host ; 7, ‘‘nucleus,” or body- rudiment of Sacculina; vr, its roots; «, definitive position of ment of the “ Sacewlina interna,” x 2. 6, Body of Sacculina ; c.t, “central tumour”; d.i, d.s, in- ferior and superior diverticula of alimentary canal of host ; 0, open- ing of perivisceral cavity of Saccu- lina ; r, its roots. the parasite. a little below it, it causes the crab’s epithelium to degenerate, so that when the crab moults, a little hole is left in this region of the same size as the body of the Saceulina, owing to the failure of the epithelium to form chitin here; and thus the little parasite is pushed through this hole and comes to the exterior as the adolescent “ Sacculina externa.” From this point onwards the crab, being inhibited in its growth through the action of the parasite, never moults again; so that the Saceulina occupies a safe position protruding from the crab’s abdomen, which laps over IV RHIZOCEPHALA——COMPLEMENTAL MALES 99 it and protects it. The remarkable features of this development are, firstly, the difficulty of understanding how the developing embryo is directed in its complicated wanderings so as always to reach the same spot where it is destined to come to the exterior ; and, secondly, the loss after the Cypris stage of all the organs and the resumption of an embryonic undifferentiated state from which the adult is newly evolved. A certain parallel to this history is found in that of the Monstrillidae, described on pp. 64-66. The Rhizocephala are hermaphrodite with the possible exception of Sy/on, which appears to be female and perhaps parthenogenetic, no male having been seen ; but unlike most other hermaphrodite Cirripedes, they reproduce by a continual round of self-fertilisation. This is the more remarkable in that the vestiges of what appears to be a male sex are still found in Sacculina and Peltogaster; certain of the Cypris larvae in_ these genera, instead of fixing on and inoculating other crabs, become attached round the mantle-open- ings of young parasites of the same species as themselves, which have recently attained to the ex- terior of their hosts (Fig. 71). These larvae, which remind us of the complemental males in Scal- pellum, ete., never produce sper- matozoa, but rapidly degenerate Fic. 71. — Fourteen Cypris larvae where they are fixed, and appear fixed round the mantle-opening never to play any role in the repro- ge a young Sacculina externa, duction of their species. The nature of this remarkable phenomenon, together with the sexual condition of the Cirripedes in general, will be discussed in the next section. Much remains to be elucidated in the life-histories of these curious animals, and it seems probable that intermediate stages may exist, showing us how the extreme discontinuity of develop- ment has been reached. Suggestive in this respect is the newly discovered parasite of the Isopod, Calathura, which the author has named Duplorbis calathurae.. This animal does not appear 1G. Smith, Fauna u. Flora d. Golfes v. Neapel, Monogr. xxix., 1906, pp. 60-64, 119-121. TOO CRUSTACEA CHAP. to possess a root-system, but is attached to its host by a tube ‘ which passes right through the mesentery and opens into the mantle-cavity of the parasite. It may be suggested that this tube corresponds to the stalk of the normal Cirripede, but its exact mode of formation would certainly throw much light on the question of Rhizocephalan development. Phenomena of Growth and Sex in the Crustacea. In the foregoing account of the Cirripedia we have met with certain peculiar sexual relations in which closely allied species exhibit marked differences in regard to the distribution of the qualities of sex among their individuals; we have seen that the majority of species are hermaphrodite, unlike most Crustacea which, with the other exception of the parasitic Isopoda, are normally dioecious; and that in some species complemental males exist side by side with the hermaphrodites, while, in yet others, the individuals are either females or dwarf males. Before examining the causes of these conditions, it will be opportune to consider a number of facts which throw light on the question of sex and hermaphroditism in general. We may then return to the discussion of the hermaphroditism found in particular in the Cirripedia and Isopoda. Parasitic Castration.—Giard ' was the first to observe that a number of parasites exert a remarkable influence on the sexual characters of their host, such that the generative glands become reduced, or may completely degenerate, while the secondary sexual characters become materially altered. This was proved to occur in the most widely different hosts, affected by the most widely different parasites (e.g. Crustacea, Insecta, Worms). Moreover, it was apparent that the affection. does not consist in the parasite merely destroying the generative organs, with which it often does not come into contact, but rather in the general disturbance of the metabolism set up by its presence. The most completely studied cases of parasitic castration are those of the Rhizocephalous Sacculina neglecta, parasitic on the spider-crab, Znachus mauritanicus? and of Peltogaster curvatus 1 Bull. Sc. Dép. Nord (2), 10 Ann. xviii., 1887, p. 1. bid. (8), i., 1888, p. 125 and other papers. * G. Smith, Joc. cit. chap. v. J. scorpio should be I. mauritanicus throughout this Monograph. IV PARASITIC CASTRATION IOI on the Hermit-crab, Hupagurus excavatus, var. meticulosa.’ The ordinary males of J. mauritanicus have the appearance shown in Fig. 72, A. The abdomen is small and bears a pair of copulatory styles, while the chelipedes are long and swollen. In the female (B) the abdomen is much larger and trough-shaped, . Fic. 72.—Illustrating the effect of parasitic Sacculina neglecta on Inachus mauri- tanicus, nat. size. A, Normal male ; Znachus ; B, normal female ; C, male infested by Sacculina (final stage) ; D, abdomen of infested female ; E, infested male in an early stage of its modification. and carries four pairs of ovigerous appendages; the chelae are small and narrow. Now it is found that in about 70 per cent of males infected with Sacculina the body takes on to varying degrees the female characters, the abdomen becoming broad as in the female, with a tendency to develop the ovigerous appendages, while the chelae become reduced (Fig. 72, C). This assumption of the female characteristics by the male under the influence of the parasite may be so perfect that the abdomen and chelae become typically female in dimensions, while the abdomen develops not only the 1. A. Potts, Quart. J. Aiier. Sev. 1., 1906, p. 599: 102 CRUSTACEA CHAP. copulatory styles typical of the male, but also the four pairs of ovigerous appendages typical of the female. The parasitised females, on the other hand, though they may show a degenerate condition of the ovigerous appendages (Fig. 72, D), never develop a single positively male characteristic. On dissecting crabs of these various categories it is found that the generative organs are in varying conditions of degeneration and disintegration. The most remarkable fact in this history is the subsequent behaviour of males which have assumed perfect female external characters, if the Sacculina drops off and the crabs recover from the disease. It is found that under these circumstances these males may regenerate from the remains of their gonads a perfect hermaphrodite gland, capable of producing mature ova and spermatozoa. The females appear quite incapable, on the other hand, of producing the male primary elements of sex on recovery, any more than they can produce the secondary. Exactly analogous facts have been observed in the case of the hermit- crabs parasitised by Peltogaster, but here the affected males produce small ova in their testes before the parasite is got rid of. Here, too, the females seem incapable of assuming male characters under the influence of the parasite. = To summarise shortly the conclusions to be deduced from these facts—certain animals react to the presence of parasites by altering their sexual condition. This alteration consists in the female sex in an arrest of reproductive activity, in the male sex in the arrest of reproductive activity coupled with the assumption of all the external characters proper to the female. 3ut in these males it is not merely the external characters that have been altered; their capacity for subsequently developing hermaphrodite glands shows that their whole organisation has been converted towards the fémale state. That this alteration consists im a reorganisation of the metabolic activities of the body is clearly suggested, and in the succeeding paragraph we furnish some further evidence in support of this view. Partial and Temporary Hermaphroditism. High and Low Dimorphism. The reproductive phases of animals are frequently rhythmic, periods of growth alternating with periods of reproduction. IV TEMPORARY HERMAPHRODITISM 103 This is well exemplified in the case of the ordinary males of Inachus mauritanicus, of some other Oxyrhynchous crabs, and of the Crayfish Cambarus." During the breeding season the males of J. mauritanicus fall into three chief categories: Small males with swollen chelae (Fig. 75, A), middle-sized males with flattened chelae (B), and large males with enormously swollen chelae (C). On dissecting specimens of the first and third categories it is found that the testes occupy a large part of the thoracic cavity and are full of spermatozoa, while in the middle-sized males Fie. 73.—Inachus mauritanicus, x 1. A, Low male; B, middle male; C, high male ; the great chela of the right side is the only appendage represented. with female-like chelae the testes appear shrivelled and contain few spermatozoa. These non-breeding crabs are, in fact, under- going a period of active growth -and sexual suppression before attaining the final state of development exhibited by the large breeding males. This phenomenon is obviously parallel to the “high and low dimorphism”? so common in Lamellicorn beetles, where the males of many species are divided into two chief categories, viz. “low males” of small size in which the secondary sexual characters are poorly developed, and “high males” of large size in which these characters are propor- ! Faxon, Ann. Mag. Nat. Hist. (5), xiii., 1884, p. 147. 2G. Smith, Mitth. Zool. Stat. Neapel, xvii., 1905, p. 312. 104 CRUSTACEA CHAP. tionately much more highly developed than in the low males. The only difference between the two cases is that whereas in the beetles growth ceases on the attainment of maturity in the low degree, in the Crustacea the low male passes through a period of growth and sexual suppression to reach the high degree of development. ~The condition of the middle-sized males may be looked upon as one of partial hermaphroditism, indications of the female state being found in the flattened chelae and in the reduced state of the testes. This interpretation is greatly strengthened by the state of affairs observed in the life-history of the male Sand-hoppers, Amphipods of the genus Orchestia.’ In the young males of several species of this genus, at the time of year when they are not actively breeding, small ova are developed in the upper part of the testes of more than half of the male individuals, these ova being broken down and reabsorbed as the breeding season reaches its height. Nor is this phenomenon confined to this genus; in the males of a number of widely different Crustacea these small ova are found in the testes at certain periods of the life-history (e.g. Astacus*), when the animal is not breeding. The foregoing facts indicate unmistakably that the males of a number of Crustacea under certain metabolic conditions, 7.e. when a stage of active growth as opposed to a stage of re- productive activity is initiated, alter their sexual constitution in such a way that the latent female characteristics are developed, and the organism appears as a partial hermaphrodite. In the preceding paragraph we saw that the males of a number of animals, especially Crustacea, react to the metabolic disturbance set up by the presence of a parasite in exactly the same way, i.e. by developing into partial or total hermaphrodites. From these two converging bodies of facts we may conclude, firstly, that sex and metabolism are two closely connected phenomena ; and, secondly, that the male sex is especially liable to assume hermaphrodite characters whenever its metabolic requirements are conservative, assimilatory, or in a preponderating degree anabolic, as When a phase of active growth is initiated, or the drain on the system, due to the presence of a parasite, is to be made good. 'C, L. Boulenger, Proc. Zool. Soc. 1908, p. 42. * Garnier, C.R. Soc. Biol. liii., 1901, p. 38. lV NORMAL HERMAPHRODITISM 105 Normal Hermaphroditism in Cirripedia and Isopoda Epicarida. The above-mentioned groups contain the only normally hermaphrodite Crustacea, and since they are in most respects highly specialised, we may be certain that they have been secondarily derived from dioecious ancestors. They both lead a sessile or parasitic life, and it is noteworthy that this habit is often associated with hermaphroditism, e.g. in Tunicates. gr ay y Dal! 106 CRUSTACEA CHAP. of small ova in their generative glands, which, however, never come to maturity. The condition of the degenerate males in the Rhizocephala may also be interpreted in the same manner. These never pass beyond the Cypris stage of development, in which they resemble in detail the Cypris larvae of the ordinary hermaphrodite individuals, and they are quite useless in the propagation of their species. It is more reasonable to suppose that these Cypris larvae, which fix on the mantle-openings of adult parasites, are in reality identical with the ordinary Cypris which infest crabs and develop into the hermaphrodites, than that they represent a Whole male sex doomed beforehand to uselessness and degenera- tion. If we suppose that the Cirripedes have passed through a state of protandric hermaphroditism similar to that of the ‘Isopoda Epicarida, it is plain that all the larvae must have originally possessed the instinct of first fixing on the adult parasites, and we may suppose that this instinct has been retained in the Rhizocephala, but is now only actually fulfilled by a certain proportion of the larvae, which, under existing circumstances, are useless and fail to develop further; while the rest of the larvae, not finding an adult parasite to fix upon, go straight on to infect their hosts and develop into the adult hermaphrodites. The same explanation would apply to the complemental males in Sea/pellum, etc., these individuals being also potential hermaphrodites, which are arrested in development, though not so completely as in the Rhizocephala, owing to the position they have taken up. This theory throws light on another dark feature of Cirripede life-history, namely, the gregarious instinct. The associations of Cirripedes are not formed by a number of Cypris larvae fixing together on the same spot, but rather by the Cypris larvae seeking out adolescent individuals of their own species and fixing on or near them. Now, if we suppose that the Cirripedes have passed through a condition of protandric hermaphroditism similar to that of the Isopoda Epicarida, it is clear that a slight modification of the sexual instinct of the larvae would lead to the gregarious habit, while its retention in some individuals in its original form accounts for their finding their way to the Iv OSTRACODA 107 mantles of adult imdividuals and developing into the so-called complemental males. Certain Cirripedes, viz. certain species of Scalpellum and Tbla and all the Acrothoracica, are dioecious. It is impossible to decide at present whether these species retain the primitive dioecious condition of the ancestral Cirripedes, or whether they too have been derived from an hermaphrodite state, but in the present state of knowledge they hardly affect the validity of the theory that has been proposed to account for the nature of the complemental males and the hermaphrodite individuals. Order IV. Ostracoda. The Ostracoda are small Crustacea, the body consisting of very few—about eight—segments, and being completely enclosed in a carapace, which has the form of a bivalve shell. Develop- ment is direct, without a Nauphus stage. The Ostracoda’ are marine and fresh-water animals that can be divided into several families, differing slightly in habits and in structures correlated with those habits. The Cypridae and Cytheridae include all the fresh-water and a vast majority of marine genera, adapted for a sluggish life among water-plants, though some can swim with consider- able activity. The common Cypris and Candona of our ponds and streams are familiar instances. The move- ments of these animals are effected by means of the two pairs of uni- ramous pediform antennae which move together and in a vertical straight line. pyre, 74,—Cundona reptans. A, In the Cypridae (Fig. 74) there are, Natural size; B, x 15. a, Ist A . : ; antennae; 6, 2nd antennae ; besides the mandibles, two pairs of c, walking legs. (After Baird.) maxillae, a pair of walking legs, and, lastly, a pair of appendages, which are doubled up into the carapace, and are used for cleaning purposes. In the marine Cytheridae there is only one maxilla, the last three appendages ' Claus, Untersuchungen zur Erforschung des Crustaceensystems, Wien, 1876. Brady and Norman, ‘‘ Monograph of the Marine and Fresh-Water Ostracoda of the N. Atlantic,” Zrans. R. Dublin Soc. (2) iv., 1889, p. 63. Miller, Fauna und Flora G. von Neapel, Monogr. xxi., 1894; ‘‘ Deutschlands Siisswasser-Ostracoden,” Chun’s Zoologica, xii., 1900. 108 CRUSTACEA—OSTRACODA CHAP. being pediform and used in walking. The telson in the Cytheridae is rudimentary, but is well developed in the Cypridae. The heart is altogether absent. In many of the fresh-water forms, ¢.g. common species of Candona and Cypris, males are never found, and parthenogenetic reproduction by the females appears to proceed uninterruptedly. Weismann! kept females of Cypris reptans breeding partheno- genetically for eight years. He also remarks on the fact that these, and indeed all parthenogenetic female Ostracoda, retain the receptaculum seminis, used normally for storing the spermatozoa derived from the male, unimpaired. Some of the Cytheridae occur in deep water. Thus Cythere dictyon was frequently taken by the Challenger in depths of over 1000 fathoms, but the majority prefer shallow water. The Halocypridae and Cypridinidae comprise marine genera pba 2] ao / ——. S { = : ZG ZZ, S y “thee iJ E (\ iw i> IS y * . AM j / \\\ “FOTW Fia. 75.—Asterope oblonga, , removed from its carapace, x 25. A, Alimentary canal; A,, Ao, Ist and 2nd antennae ; H, eye; @, gills; G@.O, generative opening ; H, heart; M, mandible; 7, 6th appendage ; 7’, last appendage (cleaning foot). (After Claus. ) of a pelagic habit. The first antennae are chiefly sensory, but the second antennae are biramous, and they do not merely move up and down, as in the preceding families, but sideways like ' «The Germ Plasm,” Contemp. Science Series, 1893, p. 345. i CLASSIFICATION 109 oars, the valves of the shells being excavated to admit of free movements. There are two pairs of maxillae; the succeeding limbs differ in the two families. In the Cypridinidae, e.g. Asterope (Fig. 75), the first leg (T) is lamelliform and is used as an accessory maxilla, while the second leg (T’) is turned upwards into the shell as a cleaning organ. In the Halocypridae the first leg is pediform, and differs in the two sexes, while the second leg is rudimentary and points backwards. In P Lf , é = ia * 2 ' 9 ata ne Le yi ' nf 4 a ea i > i i « i - 2 F ae I : : “ “ . ‘ ‘ ; , is : y. i oo ‘ ( o- L ‘ al 7 : ' 4 P rr annals a x we Psd ee rt s a cris E jaee CHAPTER IX ARACHNIDA—INTRODUCTION Tue Arachnida, together with the Crustacea, Insecta, Myriapoda, and Peripatus, make up the great phylum Arthropoda, a phylum which, from the point of view of numbers of species and of individuals, is the dominant one on this planet, and from the point of view of intelligence and power of co-operating in the formation of social communities is surpassed but by the- Vertebrata. The Arachnida form a more diverse class than the Insecta; they differ, perhaps, as much inter se as do the Crustacea, and in structure as in size and habit they cover a wide range. Lankester in his article upon the Arthropoda, in the tenth edition of the Encyclopaedia Britannica, dwells upon the fact that whereas the adult Peripatus has but one persisting seg- ment in front of the head, and its mouth is between the second persisting appendages, in Arachnids the mouth has receded and lies between the bases of the appendages (pedipalpi) of the third persisting segment, while two of the persisting segments, those of the eyes and chelicerae, have passed in front of the mouth. This process has continued in the Crustacea and in the Insecta; in both of these classes there are three embryonic segments in front of the adult mouth, which lies between the appendages of the fourth segment. In the larger and more complex Arachnida the number of segments is fixed and constant, and though possibly no adult member of the group, owing to the suppression of one or more seoments during the ontogeny, ever shows the full number at any one time, the body can be analysed into twenty-one segments. It is interesting to note that the same number of segments occurs in 255 256 ARACHNIDA (INTRODUCTION) CHAP. Insecta and in the higher Crustacea.'. The significance of this fact is not perhaps apparent, but it seems to indicate “a sort of general oneness, if I may be allowed to use so strong an ex- pression,” as Mr. Curdle said when discussing the unities of the drama with Nicholas Nickleby. These segments are arranged in higher categories or “ tagmata,” of which we can recognise three: (i.) the prosoma, (i1.) the mesosoma, and (iii.) the metasoma. The prosoma, sometimes termed the “cephalothorax,” includes all the segments in front of the genital pore. According to this definition the prosoma includes the segment which bears the chilaria in Limulus (the King-crab) and the pregenital but evanescent segment in Scorpions. The mesosoma begins with the segment bearing the genital pore, and ends with the last segment which bears free appendages, six segments in all. The metasoma also consists of six segments which have no appendages; together with the mesosoma it forms the abdomen of some writers. The anus lies posteriorly on the last segment, and behind it comes in the higher forms a post-anal “telson,” taking in Scorpions the form of the sting, in King-crabs that of the spine. As we have seen, it is only in the more typical and perhaps higher forms that we can find our twenty-one segments, and then they are never present all at once. In many groups of Arachnids the number is reduced at the hinder end, and obscured by the fusion of neighbouring segments. Also segments are dropped as a stitch is dropped when knitting; for instance, in the rostral segment which has a neuromere, and in the Spider Trochosa vestigial antennae, or in Scorpions the pre-genital segment. Primitive Arachnids appear to have lived in the sea and to have breathed by gill-books borne on appendages; when their descendants took to living on land and to breathing air instead of water, the gill-books sank into the body and became lung- books, to which the air was admitted by slit-like stigmata. In other terrestrial forms the lung-books are replaced by tracheae which in their structure and arrangement resemble those of Peripatus rather than those of the Insecta. The circulation, as 1 This can be maintained in the Crustacea by counting the seventh abdominal segment, which appears in Gnathophausia ; but this is not universally regarded as a true segment. See also Vebalia (p. 111). Ix ANATOMY 257, is usual in Arthropods, is largely lacunar, but in Scorpions and Jimulus the arteries form definite channels, and are in fact better developed than in any other Arthropod. As a rule the alimentary canal in Arachnids is no longer than the distance between the mouth and the anus; but in the King-crab, where the mouth is pushed back almost to the centre of the body, there is a flexure in the median vertical plane. Paired glands, usually called the liver, open into the mesenteron ; food passes into the lumen of these glands, and is probably digested there. In many Arachnids these glands extend into the limbs. In those members of the group that have become terrestrial the nitrogenous excreta are separated out by Mal- pighian tubules which open into the proctodaeum; but coxal glands, homologous with the green gland and shell-glands of Crustacea, may coexist, and in the aquatic Limulus these alone are found. They usually open on the base of one or more pairs of walking legs. The endosternite, or internal skeletal plate to which muscles are attached, reaches a higher development in the Arachnida than in the Crustacea. In Scorpions it forms a kind of diaphragm incompletely separating the cavities of the pro- and meso-soma. The supra-oesophageal ganglion supplies the two existing segments which have slipped before the mouth, ze. those of the eyes and of the chelicerae. The post-oral ganglia in the Acarina, the Pedipalpi, the Solifugae, and the Araneae have fused into a central nerve-mass, from which nerves radiate; but in Limulus the prosomatic appendages are all supplied from the nerve-ring. The chief sense-organs are eyes of the characteristic Arthropod type, and sensory hairs of a great variety of complexity. Scorpions and Spiders have stridulating organs, and we may assume that they have also some auditory apparatus; perhaps some of the hairs just mentioned act as hearing organs. Arachnids are male and female; they do not reproduce asexually, and there is no satisfactory proof that they ever repro- duce parthenogenetically. As a rule there is little external difference between the two sexes, except in Spiders, where the male is as a rule smaller than the female, and when adult has the pedipalpi modified for use in depositing the spermatophores. The ovaries and testes are annular, and with their ducts encircle the alimentary canal in Mites and Phalangids; in Scorpions and VOL. IV S 258 ARACHNIDA (INTRODUCTION) CHAP. IX King-crabs they have become retiform. Mites, Scorpions, and Pedipalps are viviparous, their eggs developing in the ovary or in a uterus. Other Arachnids lay eggs, and many Spiders and Pseudoscorpions carry their eggs about with them. As a rule the young is but a miniature of the parent, and the Arachnid, unlike the Crustacean or Insect, undergoes little or no meta- morphosis. A certain number of Mites are parasitic in plants and in animals, and a few, together with a few Spiders, have resumed the aquatic life of their remote ancestors. The members of some Orders, such as the Solifugae and Opiliones, are nocturnal, and many are provided with silk-glands and weave webs which reach their highest pitch of perfection amongst the Spiders. At times—especially is this the case with the Mites—enormous numbers of individuals live together, but they never show the least adaptation to communal life, and no individuals are ever specialised to perform certain functions, as is the rule in com- munities of social Insects. With the two exceptions that we regard the Trilobites as more nearly allied to the Crustacea, and have therefore considered them apart, and have treated the Pycnogonida independently of the Arachnida, we have followed Lankester in his classification, though not always in his nomenclature :— Sub-class 1. Delobranchiata! (Mero- stomata). Order (i.) Xiphosura. Order (ii.) Eurypterida ( = Gig- antostraca, Extinct). Sub-class 2. Embolobranchiata. Order (i.) Scorpionidea. Order (ii.) Pedipalpi. Order (i1i1.) Araneae, Order (iv.) Palpigradi. Order (v.) Solifugae. Order (vi.) Chernetidea (= Pseu- doscorpiones). Order (vii.) Podogona. Order (viii.) Phalangidea (= Opi- liones). Order (ix.) Acarina, - APPENDICES (i.) Tardigrada. (ii.) Pentastomida. 1 This and the following Sub-class correspond with Lankester’s Sub-class Euarachnida. The Delobranchiata have gills patent and exposed, and adapted for breathing oxygen dissolved in water. The Embolobranchiata have either the gill- books (now termed lung-books) sunk into their body, or the gill-books are wholly or partially replaced by tracheae. In either case the members of this Sub-class breathe atmospheric oxygen. CHAPTER X ARACHNIDA (CONTINUED )—DELOBRANCHIATA = MEROSTOMATA— XIPHOSURA SUB-CLASS I—DELOBRANCHIATA = MEROSTOMATA. Order I. Xiphosura.' In his recent classification of the Arachnida, Lankester’ has grouped the Xiphosura or King-crabs with the extinct Euryp- terids or Gigantostraca under the name of Delobranchiata, better known under the name Merostomata® of Dana. The chief character of this group, and one which differentiates it from all the animals placed together by Lankester in the group Embolo- branchiata, is that they have gills patent and exposed. The Niphosura are, in fact, with the exception of a few marine Mites, the only Arachnids which now lve in the sea as did their allies the Eurypterids in Palaeozoic times. With a few fresh-water exceptions, all other Arachnids have taken to life on land, and with a change from water-breathing to air-breathing came a change in the respiratory system, the gills becoming “ lung-books,” or possibly tracheae, or disappearing altogether. 1 Woodward, ‘‘On some Points in the Structure of the Xiphosura, having reference to their relationship with the Eurypteridae,”’ Quart. J. Geol. Soc. xxiii., 1867, p. 28, and xxviii., 1871, p. 46. Milne Edwards, A., “ Recherches sur l’anat. des Limules,” Ann. Sci. Nat. (5), xvii., 1873, Art. 4. Lankester, E. R., ‘‘ Limulus an Arachnid,” Quart. J. Micr. Sei. xxi., 1881, p. 504. Kingsley, J. S., ‘‘The Embryology of Limulus,” Journ. Morph. vii. p. 35, and viii. p. 195, 1892-3. Kishinouye, ‘‘On the Development of Limulus longispina,” Journ. Coll. Sci. Japan, v., 1892, p. 53. Patten, W., and Redenbaugh, W. A., ‘‘ Studies on Limulus,” Journ. Morph. xvi., 1900, pp. 1, 91. 2 Quart. J. Micr. Sci. xlviii., 1905, p. 165. ° unpds=a thigh. 259 260 ARACHNIDA—XIPHOSURA CHAP. A few years ago Pocock re-classified the Xiphosura, and his classification will be found on pp. 276, 277. It will be noticed that in his classification the generic name Limulus has disappeared. I have, however, retained it in this article, partly because I regard the name as so well established that every one knows what it denotes, and partly because in a group which contains confessedly very few species, differing inter se comparatively slightly, it seems unnecessary to complicate matters with sub-families and new names. Looked at from above a Limulus presents a horse-shoe-like outline, from the posterior end of which projects a long spine. It is often called in America the Horsefoot-crab, but its common or vulgar name is the King-crab. Across the middle of the body is a joint, and this joint separates the prosoma from the meso- and meta-soma which are in Kine-crabs fused together. The prosoma comprises all the segments up to and including the segment which carries the chilaria;' the mesosoma begins with the segment bearing the genital pores, and ends with the last segment which bears appendages ; the metasoma comprises all the segments posterior to the last segment which carries appendages. The prosoma corresponds with the “cephalothorax” of some authors, and the meso- plus the meta-soma are equivalent to their “abdomen.” Dorsally, then, the prosoma is a vaulted structure with a smooth, horse-shoe-shaped anterior and lateral margin. — Its posterior edge, the line where the meso- plus the meta-soma are hinged, is a re-entrant bay with three sides. The meso- and meta-soma are in the King-crabs fused together and form a hexagon. Three sides of this hexagonal double region form the hinge, two form the lateral margins and slope inwards; these bear six fused and six jointed spines which have a segmental value. The sixth or posterior side is indented, and its concavity forms the area to which the large postanal, unsegmented tail or spine is hinged. The whole body is covered by a smooth chitinous sheath varying from sage-green to black in colour, and it is kept very clean, probably by some excretion which hinders various sessile animals attaching themselves to it as they do, for instance, on 1 This segment, though present in embryo Scorpions, has disappeared in the adults of those animals. x KING-CRABS 261 many Copepods. Burrowing animals lke Limulus are usually free from these messmates. King-crabs have a self-respecting, well-groomed appearance. On the rounded dorsal surface the chitinous covering is produced into a certain number of spines Fic. 152.—Dorsal view of the King-crab, Limulus polyphemus, x 4. From Shipley and MacBride. 1, Carapace covering prosoma; 2, meso- and meta-soma ; 3, telson ; 4, median eye ; 5, lateral eye. arranged in a median and two lateral rows. The anterior median spine overhangs the median eyes, and the anterior lateral spine on each side overshadows the large lateral eyes. The vaulted carapace is turned in on the under side, where there is a flat rim which widens anteriorly, and on the inner edge this rim borders a sunken area, into the concavity of which ARACH NIDA—-XIPHOSURA CHAP. No OV tN the numerous appendages project. Thus, although when viewed from above a Limulus looks as though it had a solid body shaped something like half a pear, when viewed from below, especially if the appendages be removed, it will be found that the Fic. 153.—Ventral view of the King-crab, Limulus polyphemus, x 4. From Shipley and MacBride. 1, Carapace covering prosoma; 2, meso- and meta-soma; 3, telson ; 4, chelicera ; 5, pedipalp ; 6, 7, 8, 9, 83rd to 6th appendages, ambulatory limbs ; 10, genital operculum turned forward to show the genital apertures; 11, 12, 13, 14, 15, appendages bearing gill-books ; 16, anus; 17, mouth; 18, chilaria. body is thin and hollowed, and almost leaf-like, as if most of the edible part of the half-pear had been scooped out. Within the hollow thus formed the appendages le, and here they move about, seldom or never protruding beyond the edge of the carapace,—in fact, all except the pedipalps and ambulatory legs are too short to project beyond this limit. x SEGMENTATION 263 The body of a King-crab can be analysed into twenty-one segments, but these do not all persist to the adult stage. They are grouped together in higher aggregates, or “ tagmata” as Lankester calls them, and most of the segments bear paired appendages. The segments with their respective appendages and _ their grouping into tagmata are shown in the following scheme :— Appendages. I. Segment Median eyes Preoral ie rs Rostrum rpc PTT: $5 Chelicerae a IVE ae Pedipalpi Lateral to mouth V. as 1st Walking Legs Postoral ~ Prosoma WAL 3 2nd Walking Legs ae WAN a 3rd Walking Legs re VIII. nh 4th Walking Legs a [X. ia Chilaria 3 xX = Genital operculum a XI. ~ 1st Gill-books a XII. - 2nd Gill-books st | M MMT. * 8rd Gill-books af SURG XIV. Fes 4th Gill-books S | XV. An 5th Gill-books Fe XVI. sf No appendages 53 XVII 6 aS » ee a y4 a Metasoma XX. 9 oe) ee) XXI1. ” ” ” We have followed Carpenter‘ in inserting the rostral segment. This corresponds with the segment that in Insects and Crustacea bears the antennae or first antennae respectively, the absence of these organs being one of the characteristic but negative features of all Arachnids. The evidence for the existence of this evanes- cent segment rests partly upon the observation of von Jawor- owski* on the vestigial feelers in an embryo Spider, 7rochosa, and perhaps more securely on the fact that, according to Korschelt and Heider, there is a distinct neuromere for this segment, between the proto-cerebral neuromere which supplies the eyes and the trito-cerebral neuromere which supplies the chelicerae. According to Brauer * the chelicerae of Scorpions are also supplied by the third neuromere. The bases of the chelicerae do not limit the mouth, but between and behind them: is a ridge or tubercle which has the 1 Quart. J. Micr. Sci. xlix., 1906, p. 469. 2 Zool. Anz. xiv., 1891, pp. 164, 173. ® Zeitschr. wiss. Zool. lix., 1895, p. 351. 264 ARACHNIDA—XIPHOSURA CHAP. same relationship to the mouth of Zimulus that the labrum has in Insects and some Crustacea. Posteriorly the mouth is bounded by the “ promesosternite,” a large median plate which lies between the bases of the ambulatory limbs. The pedipalps and all the ambulatory limbs have their bases directed towards the mouth, their gnathobases or sterno-coxal processes are cushion-like structures covered with spines—all pointing inwards —and with crushing teeth. They form a very efficient man- ducatory apparatus. The boundary of the mouth is finally completed by the chilaria. Certain of the appendages which persist will be described with the functions they subserve, the eyes with the sense-organs, the genital operculum with the generative organs, the gill-books with the respiratory system, but the chelicerae, pedipalpi, and walking limbs, which have retained the functions of prehension and locomotion usual to limbs, merit a little attention.’ The chelicerae are short and composed of but three joints. They are, like the succeeding segments, chelate, and the chelae of all are fine and delicate like a pair of forceps rather than like a Lobster’s claw. In the female Z. polyphemus the pedipalp is remarkably like the three ambulatory legs which succeed it, and all four are chelate, but in the adult male the penultimate joint of the pedi- palp is not prolonged to form one limb of the chela, which is therefore absent, and the appendage is thicker and heavier than in the other sex. In Z. longispina and L. moluccanus the first walking leg, as well as the pedipalp, ends in a claw and not in a chela; the immature males resemble the females. The first three walking legs in both sexes of LZ. polyphemus resemble the pedipalpi of the female, and like them have six joints. The fourth and last pair of ambulatory appendages is not chelate, but its distal joints carry a number of somewhat flattened structures, which are capable of being alternately divaricated and approximated or bunched together. This enables them to act as organs for clearing away sand or mud from beneath the carapace as the creature lies prone on the bottom of the sea. To quote Mr. Lloyd,” the “two limbs are, sometimes alternately and sometimes simultaneously, thrust backward below the carapace, quite beyond the hinder edge 1 They are described in great detail in Lankester’s article, ‘‘ Limulus an Arachnid,” Quart. J. Mier. Sci. xxi., 1881, p. 504. nN. (SOCA SSVI eas oe vale x HABITS f 265 of the shell; and in the act of thrusting, the lobes or plates on each leg encounter the sand, the resistance or pressure of which causes them to open and fill with sand, a load of which at every thrusting operation is pushed away from under the king-crab, and deposited outside the carapace. The four plates then close and are withdrawn closed, previous to being opened and charged with another load of sand; and at the deposit of every load the whole animal sinks deeper into its bed, till it is hidden all except the eyes.” There seems little doubt that the action of these appendages in removing the sand from under the carapace is reinforced by the fanning action of the respiratory appendages, which set up a current that helps to wash the particles away. But the posterior walking legs are not the only organs used in burrowing. The Rey. Dr. Lockwood,’ who observed the habits of L. polyphemus off the New Jersey coast, says, “The king-crab delights in moderately deep water, say from two to six fathoms. It is emphatically a burrowing animal, living literally in the mud, into which it scoops or gouges its way with great facility. In the burrowing operation the forward edge of the anterior shield is pressed downward and shoved forward, the two shields being inflected, and the sharp point of the tail presenting the fulcrum as it pierces the mud, whilst underneath the feet are incessantly active scratching up and pushing out the earth on both sides. There is a singular economy of force in this ex- cavating action ; for the doubling up or inflecting and straighten- ing out of the two carapaces, with the pushing purchase exerted by the tail, accomplish both digging and subterranean progression.” At night-time Zimulus is apt to leave the sand and progress by a series of short swimming hops, the respiratory appendages giving the necessary impetus, whilst between each two short flights the animal balances itself for a moment on the tip of its tail. During this method of progressing the carapace is slanting, forming an angle of about 45° with the ground. The unseg- mented tail is also used when a King-crab falls on its back. “The spine is then bent, ze. its point is planted in the sand so that it makes an acute angle with the carapace, which is then so far raised that some of the feet are enabled to grasp a projecting surface, either longitudinal or vertical, or at some combination of the two; and the crab then turns over.” 1 Tr. Linn. Soc. xxviii., 1872, p. 472. 266 ARACHNIDA—XIPHOSURA CHAP: Fic. 154. —A sagittal section of Limulus, seen from the right side, somewhat smaller than natural size. After Patten and Reden- baugh. All the prosomatic appendages, except the chelicera (4) and chilarium (33) of the right side, are omitted. The genital oper- culum (32) and the five gills (28) are repre- sented. The muscles are omitted except the fibres running from the occipital ring to the pos- terior side of the oesophagus, the chilarial muscles, the sphincter ani (27), and the levator ani (24). The endosternite (34), with the occipital ring and the capsuliginous bar, is seen from the side, and the positions of the abdominal endochondrites (31) are indicated. The mouth (1) leads into the oesophagus, which passes through the brain to the proventriculus (12). A constriction, which marks the position of the pyloric valve, separates the proventriculus from the in- testine (23) which passes posteriorly to the anus (26). A pair of hepatic ducts (15) enter the intestine opposite the endo- cranium. The heart (16) surrounded by the peri- cardial sinus lies above the intestine. The pericardium is shown between the heart and the intestine. The ostia (17) of the heart and the origins of the four lateral arteries (19) are indicated; the frontal artery (13) and the aortic arches (14) curving down to the brain, arise from the anterior end of the heart; the superior abdominal artery and the opening of the collateral artery into it are shown. The brain surrounding the oesophagus is seen in side view upon the neural side of the endosternite (34). The ventral cord (35) passes through the occipital ring into the abdominal region. The anterior commis- sure (3), with the three rostral nerves (2) innervating the rostrum, or labrum, and four of the post-oral commissures, are re- presented. The cheliceral nerve with the small external pedal branch is shown entire, but the next five neural nerves are cut off. The chilarial nerve, the opercular nerve, and the five branchial nerves, enter their respective appendages, the two former pass- ing through the occipital ring. From the fore-brain the three olfactory nerves (5) pass anteriorly to the olfactory organ ; the median eye-nerve (10) passes to the right of the proventriculus (12) to the median eyes (11) ; the lateral eye-nerve (7) passes forward and is represented as cut off opposite the proventriculus. The lateral nerve (9) or first haemal nerve is also cut xX ANATOMY—HABITS 267 off just beyond the point where it fuses with the second haemal nerve (8). The stomodaeal nerve (6) ramifies over the oesophagus and proventriculus. The second haemal nerve (8) passes to the anterior extremity of the carapace ; its haemal branch is cut off opposite the proventriculus. An intestinal branch arises from near its base and disappears behind the anterior cornu of the endo- sternite. The next three haemal nerves (36) are cut off close to the brain, and the following nine haemal nerves are cut off beyond the cardiac branches. The fifteenth haemal nerve (29) is cut off beyond its branch to the telson muscles. Both branches of the haemal nerve are represented extending into the telson (25). The intestinal nerves are shown arising from the haemal nerves and entering the intestine. Those from the sixth and seventh neuromeres pass through foramina in the endosternite, and communicate with a plexus in the longitudinal abdominal muscles before entering the intestine. The eighth passes just posterior to the endo- sternite and joins the same plexus. Those from the first four branchial neuromeres arise very near the abdominal ganglia, and are double in their origins, the anterior branches joining the above-mentioned plexus, and the posterior branches entering the intestine. The fifteenth extends far back towards the rectum and anastomoses with the sixteenth, which arises from the caudal branch of the sixteenth haemal nerve, and innervates the rectum and anal muscles. The segmental cardiac nerves (18) arise from the haemal nerves of the sixth to the thirteenth neuromeres respectively. The most anterior one passes to the inter- tergal muscles and the epidermis in the median line, but the connections with the cardiac plexus have not been made out. The next two (18) fuse to form a large nerve, which passes to the inter-tergal muscles and epidermis, but has not been observed to connect directly with the cardiac plexus. It, however, sends posteriorly a branch, the pericardial nerve (20), which in turn gives a branch to each of the cardiac nerves of the branchial neuromeres, and then continues onward to the posterior margin of the abdomen. ‘This nerve lies in the epidermis. The median and lateral cardiac nerves (22 and 21) are seen upon the walls of the heart. The five cardiac nerves from the branchial neuromeres pass, in the epidermis, to the median line, and dip down to the median nerve (22) of the heart opposite the last five pairs of ostia (17). They communicate with the pericardial nerve (20) and also with the Jateral sympathetic nerve (30). Two post-eardiac nerves pass from the first and second post-branchial nerves to the epidermis posterior to the heart. The last cardiac nerve and the two post-cardiac nerves give off branches which anastomose with each other and innervate the extensors of the telson. The lateral sympathetic nerve (30) receives branches from all the neuroineres from the eighth to the fourteenth, either through the cardiac nerves or the haemal nerves, and innervates the branchio-thoracie muscles, extending with these far into the cephalothorax. 1, Mouth ; 2, rostral nerve in labrum ; 3, anterior commissure ; 4, chelicera ; 5, olfactory nerves ; 6, stomodaeal nerve ; 7, lateral eye-nerve ; 8, 2nd haemal nerve ; 9, lateral nerve ; 10, median eye-nerve ; 11, median eye ; 12, proventriculus ; 13, frontal artery ; 14, aortic arch ; 15, anterior hepatic duct of liver ; 16, heart ; 17, 2nd ostium ; 18, 7th and 8th segmental cardiac nerves ; 19, one of the lateral arteries ; 20, pericardial nerve ; 21, lateral cardiac nerve; 22, median cardiac nerve ; 23, intestine ; 24, levator ani muscle ; 25, telson ; 26, anus ; 27, sphincter ani muscle ; 28, last branchial appendage ; 29, 15th haemal nerve; 30, lateral sympathetic nerve ; 31, 8th abdominal endochondrite ; 32, genital operculum; 33, chilarium; 34, endosternite ; 35, ventral nerve cord; 36, 6th haemal nerve ; 37, origin of 6th neural nerve. Limulus feeds partly on bivalves, but mainly on worms, especi- ally Nereids, which it catches with its chelate limbs as it burrows through the sand. The food is held immediately under the mouth by the chelicerae, aided at times by the succeeding appendages ; it is thus brought within range of the gnathobases of the 268 ARACHNIDA—-XIPHOSURA CHAP. walking legs, and these by an alternate motion “card” the food into fragments, which when sufficiently comminuted pass into the mouth. At times its appendages are caught between the valves of Venus mercenaria, a burrowing bivalve known in America as the “ quahog” or “round clam.” The Limulus has seized with its chelate claws the protruding siphon of this mollusc, which, being rapidly drawn in, drags with it the limb of the king-crab, and the valves of the clam are swiftly snapped to. As a rule in Arachnids the alimentary canal is no longer than the body, and runs straight from mouth to anus, but in Limulus, the mouth being pushed far backward, there is a median loop, and the narrow oesophagus which leads from the mouth, having traversed the nerve-ring, passes forward towards the anterior end of the carapace. Here it enters into a somewhat > shaped and spacious proventriculus; posteriorly the proventri- ulus opens by a funnel-shaped valve into the anterior end of the narrow intestine. All these structures are derived from the stomodaeum, are lined with chitin and are provided with very muscular walls whose internal surface is thrown into longitudinal ridges. The intestine runs straight backward, diminishing in its diameter, and ends in a short, chitin-lined, and muscular rectum which is derived from the proctodaeum ; the anus is a longitudinal sht. A large gland, usually called the liver, consisting of in- numerable tubules, pours its secretions into the broader anterior end of the intestine by two ducts upon each side; it extends into the meso- and meta-soma, and, together with the repro- ductive organs, forms a “packing ” in which the other organs are embedded. The contents of the alimentary canal are described as “pulpy and scanty,” and probably much of the actual digestion goes on inside the lumen of the above-mentioned gland. The vascular system of Limulus, like that of the Scorpions, is more completely developed than is usually the case in Arthro- pods. For the most part the blood runs in definite arteries, and when it passes as it does into venous lacunae these are more definite in position and in their retaining walls than in other members of the phylum. The heart lies in a pericardial space with which it communi- cates by eight! pairs of ostia. Eight paired bands of connective tissue, the “alary muscles” of authors, sling the heart to the ' A rudimentary ninth pair of ostia are described anteriorly. x VASCULAR SYSTEM—GILLS 269 pericardial membrane. Posteriorly the pericardial chamber receives five paired veins on each side coming from the gills and returning the puritied blood to the heart. Eleven arteries arise from the heart. These are (i.) a median frontal artery which, passing forward, divides into a right and left marginal artery. These run round the edge of the carapace to its posterior angle, where each receives a branch of the collateral artery mentioned below. (ii.) and (iii.) are the aortic arches (Fig. 154), paired vessels running round and supplying the proven- triculus and oesophagus. These unite ventrally in a vascular ring which encloses the nerve-ring, and is continued along the ventral nerve-cord as the ventral artery and along some of the chief nerves. This vascular ring supplies the lateral eyes and all the append- ages mentioned on p. 263 up to and including the genital oper- culum. The ventral artery supplies the respiratory appendages, and gives branches to the rectum, caudal spine, ete. Two of its branches encircle the rectum, and uniting open into the superior abdominal artery. iv.-xi. ave paired lateral arteries which leave the heart beneath the anterior four ostia, and soon enter a longi- tudinal pair of collateral arteries which unite behind in the just mentioned superior abdominal artery ; they also give off branches to the muscles and to the intestine, and a stout branch mentioned above which passes into the marginal artery posteriorly. The venous system is lacunar, and the blood is collected from the irregular spaces between the various organs into a pair of longi- tudinal sinuses, whence it passes into the operculum and the five pairs of gills) A large branchio-cardiac canal returns the blood from each gill to the cavity of the pericardium, and so through the ostia to the heart. Eight veno-pericardiac muscles run from the under surface of the pericardium to be inserted into the upper surface of the longitudinal sinus; they occur opposite the ostia, and play an important part in the mechanism of the circulation. The blood is coloured blue by haemocyanin ; amoeboid corpuscles float in the plasma. The respiratory organs are external gills borne on the posterior face of the exopodite of the lamella-like posterior five mesosomatic limbs. Each gill consists of a series of leaves like the leaves of a book, and some 150-200 in number. Within the substance of each leaf the blood flows, while without the oxygen-carrying water circulates between the leaves. These gill- 2. @ ARACHNIDA—XIPHOSURA CHAP. bearing appendages can be flapped to and fro, and they seem to be at times held apart by the flabellum, a spatulate process which Patten and Redenbaugh regard as a development of the median sensory knob on the outer side of the coxopodite of the last pair of walking limbs. Limulus has no trace of Malpighian tubules, structures which seem often to develop only when animals cease to live in water and come to live in air. The Xiphosura have retained as organs of nitrogen- ous excretion the more primi- tive nephridia, or coxal glands as they are called, in the Arachnida. They are red- brick in colour, and consist of a longitudinal portion on each i! R eerpegranciies teeta a ee gi ot side of the body, which gives LimnuLus, trom le posterior side, ShOW f ing the distribution of the gill-nerve to Off a lobe opposite the base of tn i bok abort natural siz). AMe™ the pedipalps and each of the of the appendage ; 2, outer lobe of first three walking -legs—in anpeage 5, median lobe of appendasss the embryo also of the cheli- neuromere ; 6, internal branchial nerve; cerae and last walking legs, but 7, gill-nerve ; 8, median branchial nerve ; : . ). external branchial nerve. these latter disappear during development. A duct leads from the interior of the gland and opens upon the posterior face of the last pair of walking legs but one. The nervous system has been very fully described by Patten and Redenbaugh, and its complex nature plays a large part in the ingenious speculations of Dr. Gaskell as to the origin of Verte- brates. It consists of a stout ring surrounding the oesophagus and a ventral nerve-cord, composed—if we omit the so-called fore-brain—of sixteen neuromeres. The fore-brain supplies the median and the lateral eyes, and gives off a median nerve which runs to an organ, described as olfactory by Patten, situated in front of the chelicerae on the ventral face of the carapace. Patten distinguishes behind the fore-brain a. mid-brain, which : x NERVOUS AND REPRODUCTIVE SYSTEMS Za < consists solely of the cheliceral neuromere, a hind-brain which supplies the pedipalps and four pair of walking legs, and an accessory brain which supplies the chilaria and the genital operculum. This is continued backward into a ventral nerve-cord which bears five paired gangha supplying the five pairs of gills and three pairs of post-branchial ganglia ; the latter are ill-defined and closely fused together. As was mentioned above, the whole of the central nervous system is bathed in the blood of the ventral sinus. The sense-organs consist of the olfactory organ of Patten, the median and lateral eyes, and possibly of certain gustatory hairs upon the gnathobases. The lateral eyes in their histology are not so differentiated as the median eyes, but both fall well within the limits of Arachnid eye-structure, and their minute anatomy has been advanced as one piece of evidence amongst many which tend to demonstrate that Limulus is an Arachnid. Both ovaries and testes take the form of a tubular network which is almost inextricably entangled with the hver. From each side a duct collects the reproductive cells which are formed from cells lining the walls of the tubes, and discharges them by < pore one on each side of the hinder surface of the genital oper- culum. As is frequently the case in Arachnids the males are smaller than the females, and after their last ecdysis the pedipalps and first two pairs of walking legs, or some of these appendages, end in slightly bent claws and not in chelae. Off the New Jersey coast the king-crabs (L. polyphemus) spawn during the months of May, June, and July, Lockwood states at the periods of highest tides, but Kingsley ' was never “able to notice any connexion between the hours when they frequent the shore and the state of the tide.” “When first seen they come from the deeper water, the male, which is almost always the smaller, grasping the hinder half of the carapace of the female with the modified pincer of the second pair of feet. Thus fastened together the male rides to shallow water. The couples will stop at intervals and then move on. Usually a nest of eggs can be found at each of the stopping-places, and as each nest is usually buried from one to two inches beneath the surface of the sand, it appears probable that the female thrusts the genital plate into the sand, while at the same time the male discharges the milt into the 1 J. Morph. vii., 1892, p. 35. 2 fie ARACHNIDA—XIPHOSURA Fig. 156.—A view of the nervous system of Zimulus from below. size.) After Patten and Redenbaugh. CHAP. (About natural ” ANATOMY 27 The carapace is represented as transparent. The appendages have been removed, but the outlines of the left entocoxites (6) have been sketched in. ‘The positions of the abdominal appendages are indicated by the external branchial muscles (17), the branchial cartilages (19), the tendinous stigmata (18), and the abdominal endo- chondrites (21). In the cephalothorax (1) all the tergo-coxal and plastro-coxal muscles have been dissected away, leaving the endosternite (11) with the occipital ring exposed. One of the left tergo-proplastral muscles (4) and the left: branchio-thoracic muscles (16) are represented. The longitudinal abdominal muscles are also seen. All the muscles of the right side have been omitted except the haemo-neural muscles (23), of which the last two are represented upon the left side also. At the base of the telson the flexors (29) and extensors (27) of the caudal spine are represented as cut off near their insertions. The sphincter ani (26), levator ani, and occludor ani (25), and their relations to the anus (28), are shown. The oesophagus runs forward to the proventriculus (3). From this the intestine (20) passes posteriorly. The brain lies upon the neural side of the endosternite, and the ventral cord (22) passes back through the occipital ring. The neural nerves are cut off, but the left haemal nerves and those from the fore-brain (12) are represented entire. The first pair of neural nerves go to the chelicerae. The second to sixth pairs go to the next five cephalothoracic appendages, which are represented by the ento- coxites (6). The seventh pair of neural nerves go to the chilaria, and the eighth pair to the operculum. The neural nerves from the ninth to the thirteenth arise from the abdominal ganglia and innervate the five pairs of gills. From the fore-brain a median olfactory nerve (9) and two lateral ones (8) pass forward to the olfactory organ; a median eye-nerve (2) passes anteriorly and haemally upon the right of the proventriculus (8) to the median eyes ; and a pair of lateral eye-nerwes pass to the lateral eyes (15). The first haemal nerve, or lateral nerve, follows the general course of the lateral eye-nerve, but continues posteriorly far back on to the neural side of the abdomen. The haemal nerves of the hind-brain radiate from the brain to the margins of the carapace, and each one passes anterior to the appendage of its own metamere. The integumentary portions divide into haemal and neural branches, of which the haemal branches (5) are cut off, Each haemal branch gives off a small nerve which turns back toward the median line upon the haemal side of the body. The haemal nerves of the accessory brain pass through the occipital ring to the sides of the body between the operculum and the sixth cephalothoracic appendage. The seventh innervates the posterior angles of the cephalothorax, the eighth the opercular portion of the abdomen. The next five haemal nerves arise from the five branchial neuromeres, pass out anterior to the gills to the sides of the abdominal carapace, and innervate the first five spines upon the sides of the abdomen. The first post-branchial nerve innervates the last abdominal spine ; the second post-branchial nerve and one branch of the third post-branchial innervate the posterior angles of the abdomen and the muscles of the telson; and the caudal branch of the third post-branchial nerve innervates the telson. Intestinal branches arise from all the haemal nerves from the sixth to the sixteenth, and pass to the longitudinal abdominal muscles and to the intestine. Cardiac nerves arise from all the haemal nerves from the sixth to the thirteenth. Six of the cardiac nerves communicate with the lateral sympathetic nerve (24), which innervates the branchio-thoracic muscles (16). Two post-cardiac nerves arise from the first two post-branchial nerves, and passing to the haemal side anastomose with a branch from the last cardiac nerve, and inner- vate the extensors (27) of the telson and the epidermis behind the heart. 1, Cephalothorax ; 2, median eye-nerve ; 3, proventriculus ; 4, tergo-proplastral muscles ; 5, haemal branch of integumentary nerve ; 6, entocoxites ; 7, 2nd haemal nerve ; 8, right olfactory nerve; 9, median olfactory nerve; 10, intestine; 11, endosternite ; 12, fore-brain; 13, origin of 4th neural nerve ; 14, lateral nerve ; 15, lateral eye ; 16, branchio-thoracic muscles; 17, external branchial muscles ; 18, tendinous stigmata; 19, branchial cartilages; 20, intestine; 21, abdominal endochondrites ; 22, ventral cord ; 23, haemo-neural muscles; 24, lateral sym- pathetic nerve ; 25, occludor ani; 26, sphincter ani; 27, extensors of telson; 28, anus ; 29, flexors of telson; 30, lateral projections of abdomen; 31, nerves of spines ; 32, external branchial muscles. VOD LV; At 274. ARACHNIDA—XIPHOSURA CHAP. water. I have not been able to watch the process more closely because the animals le so close to the sand, and all the append- ages are concealed beneath the carapace. If touched during the oviposition, they cease the operation and wander to another spot or separate and re- turn to deep water. I have never seen the couples come entirely out of the water, although they frequently come so close to the shore that portions of the carapace are uncovered.” ! The developing ova and young larvae are very hardy, and in a little sea-water, or still better packed in sea-weed, will survive long journeys. In this way they have been transported from the Atlantic to the Pacific coasts of the United States, and for a time at any rate flourished in the western waters. Three barrels full of them “consigned from Woods Holl to Sir E. Ray Lankester arrived in England with a large proportion of larvae alive and apparently well. According to Kishinouye, ZL. longispina spawns chiefly in August and between tide- marks. “The female excavates a hole about a Laie ae 15 em. deep, and deposits eggs in it while the the female Zimulus male fertilises them. The female afterwards Shean buries them, and begins to excavate the next the round “nests” hole.”? A line of nests (Fig. irene) is thus Sena ete established which is always at right angles apparently exhausted. to the shore-line. After a certain number ae: fae EE of nests have been formed the female tires, and the heaped up sand is not so prominent. In each “nest” there are about a thousand eggs, placed first to the left side of the nest and then to the right, from which Kishi- nouye concludes that the left ovary deposits its ova first and then the right. Limulus rotundicauda and L. moluccanus do not bury their eggs, but carry them about attached to their swimmerets. The egg is covered by a leathery egg-shell which bursts after a certain time, and leaves the larva surrounded only by the 1 Kingsley, Joc. cit. 2 J. Coll. Tokyo. v., 1893, p. 53. x REPRODUCTION 275 blastodermie cuticle; when ripe it emerges in the condition known as the “Trilobite-larva” (Fig. 158), so called from a superficial and misleading resemblance to a Trilobite. They are active little larvae, burrowing in the sand like their parents, and swimming vigorously about by aid of thei leaf-like posterior limbs. Sometimes they are taken in tow-nets. After the first moult the segments of the meso- and meta-soma, which at. first had been free, showing affinities with Prestwichia and Lelinurus of Palaeozoic times, become more solidified, while the post-anal tail-spine — absent in the Trilobite larva— makes its first , ‘ a Fic. 158.—Dorsal and ventral view of the last larval stage (the so-called Trilobite stage) of Limulus polyphemus before the appearance of the telson. 1, Liver; 2, median eye ; 8, lateral eye; 4, last walking leg; 5, chilaria. (From Kingsley and Takano. ) appearance. This increases in size with successive moults. We have already noted the late appearance of the external sexual characters, the chelate walking appendages only being replaced by hooks at the last moult. Limulus casts its cuticle several times during the first year Lockwood estimates five or six times between hatching out in June and the onset of the cold weather. The cuticle splits along a “thin narrow rim” which “runs round the under side of the anterior portion of the cephalic shield.”' This extends until it reaches that level where the animal is widest. Through this slit the body of the king-crab emerges, coming out, not as that of a beetle anteriorly and dorsally, but anteriorly and ventrally, in ! Lockwood, Amer. Nat. iv., 1870-71, p. 261. 276 ARACHNIDA——-XIPHOSURA CHAP, such a way as to induce the unobservant to exclaim “it is spewing itself out of its mouth.” In one nearly full-sized animal the increase in the shorter diameter of the cephalic shield after a moult was from 8 inches to 94 inches, which is an indication of very rapid growth. If after their first year they moult annually Lockwood estimates it would take them eight years to attain their full size. The only economic use I know to which Limulus is put is that of feeding both poultry and pigs. The females are preferred on account of the eggs, of which half-a-pint may be crowded into the cephalic shield. The king-crab is opened by running a knife round the thin line mentioned on p. 275. There is a belief in New Jersey that this diet makes the poultry lay; undoubtedly it fattens both fowls and pigs, but it gives a “shocking” flavour to the flesh of both. CLASSIFICATION. But five species of existing King-crabs are known, and these are grouped by Pocock into two sub-families: (1.) the Xipho- surinae, and (ii.) the Tachypleinae. These together make up the single family Xiphosuridae which is co-extensive with the Order. The following is Pocock’s classification." The names used in this article are printed in italic capitals. ORDER XIPHOSURA. Family 1. Xiphosuridae. Sub-Fam. 1. Xiphosurinae. This includes the single species Viphoswra polyphemus (Linn. ) (= LIMULUS POLYPHEMUS, Latreille), “which is said to range from the coast of Maine to Yucatan.” Sub-Fam. 2. Tachypleinae. Genus A. Tachypleus includes three species: (.) Z. gigas, Mill. (= Limulus gigas, Miill., and LZ. mozuccanus, Latreille), widely distributed in Malaysia; (i1.) 7. tridentatus, Leach (=. tridentatus, Leach, and LZ. Lonerspiva, Van der Hoeven), extending from British North Borneo to China and Southern 1 For a diagnosis of the species and a list of synonyms, see Pocock, Ann. Mag. Nat. Hist. (7), ix., 1902, p. 256. x CLASSIFICATION 2 Sy N Japan; and (iii) 7. hoeveni, Pocock (= LZ. moLUCcCcANUS, Van der Hoeven), found in the Moluccas. Genus B. Carcinoscorpius with one species, C. rotundicauda (Latreille) (= Z. rorunbicauD4, Latreille). It occupies a more westerly area than 7. gigas or than 7. tridentatus, having been recorded from India and Bengal, the Gulf of Siam, Penang, the Moluceas, and the Philippines. With regard to the affinities of the group it is now almost universally accepted that they are Arachnids. The chief features in which they differ from other Arachnids are the presence of gills and the absence of Malpighian tubules, both being features associated with aquatic life. As long ago as 1829 Straus- Diirckheim emphasised the points of resemblance between the two groups, and although the view was during the middle of the last century by no means universally accepted, towards the end of that epoch the painstaking researches of Lankester and his pupils, who compared the King-crab and the Scorpion, segment with segment, organ with organ, tissue with tissue, almost cell with cell, established the connexion beyond doubt. Lankester would put the Trilobites in the same phylum, but in this we do not follow him. With regard to the brilliant but, to our mind, unconvincing speculations as to the connexion of some Limulus- like ancestor with the Vertebrates, we must refer the reader to the ingenious writings of Dr. Gaskell,’ recently summarised in his volume on.“ The Origin of Vertebrates,’ and to those of Dr. Patten in his article “On the Origin of Vertebrates from Arachnids.” * Fossil Xiphosura.° Limulus is an example of-a persistent type. It appears first in deposits of Triassic age, and is found again in the Jurassic, Cretaceous, and Oligocene. In the lithographic limestone of Solenhofen in Bavaria, which is of Upper Jurassic age, Limulus 1s common and is represented by several species. One species is known from the Chalk of Lebanon, and another occurs in the Oligocene of Saxony. No other genus of the Xiphosura 1 Quart. J. Mier. Sci. xxxi., 1890, p. 379; Proc. Cambr. Phil. Soc. ix., 1895-1898, p: 19; J. Anat. Physiol. xxxili., 1899, p. 154. 2 Quart. J. Micr. Sci. xxxi., 1890, p. 317. 3 Tam indebted to Mr. Henry Woods for these paragraphs on fossil Xiphosura. iS) N io.) ARACH NIDA—XIPHOSURA CHAP. appears to be represented in the Mesozoic and Tertiary deposits, but in the Palaeozoic formations (principally in the Upper Silurian, the Old Red Sandstone, and the Coal Measures) several genera have been found, most of which differ from Limulus in having some or all of the segments of the ab- domen free ; in this respect they re- semble the Euryp- terida, but differ from them in the number of segments. Fic. 159.—A. Hemiaspis limuloides, Woodw., Upper Silurian, In Hemaaspis (Fig. Leintwardine, Shropshire. Natural size. (After Wood- 159, A), from the ward.) B. Prestwichia (Eurodps) danae (Meek), Carboni- @:1,,,,.:, ‘ ferous, Illinois, x §. (After Packard.) Silurian, the seg ments of the ab- domen are divisible into two groups (mesosoma and metasoma) in the same way that they are in Eurypterids; the first six segments have broad, short terga, the lateral margins of the sixth being divided into two lobes, probably indicating the presence of two fused segments; the last three segments are narrower and longer than the preceding, and at the end is a pointed tail-spine. In Belinurus (Fig. 160) from the Carboniferous, d the two regions of the abdomen are much less distinct; there are eight segments, the last Se ee three of which are fused together, and a long — Measures, Queen's tail-spine. In Neolimulus, from the Silurian, een there seems to be no division of the abdomen into two regions, and apparently all the segments were free. On the other hand, in Prestwichia (Carboniferous), all the segments of the abdomen, of which there appear to be seven only, were fused together (Fig. 159, B). In the Palaeozoic genera the median or axial part of the dorsal surface is raised and distinctly limited on each side, so presenting a trilobed appearance similar to that of Trilobites. = FOSSIL FORMS 279 In WNeolimulus, Belinurus, and Prestwichia, lateral eyes are present on the sides of the axial parts of the carapace, and near its front margin median eyes have been found in the two last- named genera. In nearly all the specimens of Palaeozoic Xiphosura! which have been found nothing is seen but the dorsal surface of the body ; in only a very few cases have any traces of the append- ages been seen,” but, so far as known, they appear to have the same general character as in Limulus. Aglaspis, found in the Upper Cambrian of Wisconsin, has been regarded as a Xiphosuran. If that view of its position is correct, then Aglaspis will be the earliest representative of the group at present known. Other genera of Palaeozoic Xiphosura are Bunodes, Bunodella, and Pseudoniscus in the Silurian ; Pro- tolimulus in the Upper Devonian; and Prolimulus in the Permian. 1 The British fossil forms of this group are described and figured by H. Wood- ward, ‘‘ Monograph of the Merostomata,” Palaeontogr. Soc. 1866-78, and Geol. Mag. 1907, p. 539. 2 Packard, ‘‘Carb. Xiphos. N. America,” Mem. Nat. Acad. Sci. Washington, ili., 1885, p. 146, pl. vi. fig. la, pl. v. fig. 3a (restoration). Williams, Amer. Journ. Sct. (3), xxx., 1885, p. 45. Fritsch, Fauna d. Gaskohle, iv., 1901, p. 64, pl. 155, figs. 1-3, and text-figures, 369, 370. ‘ay vi 5 mee EURYPTERIDA BY HENEY WOODS, M.A. St. John’s College, Cambridge, University Lecturer in Palaeozoology. CHAPTER XI ARACHNIDA (CONTINUED)—DELOBRANCHIATA = MEROSTOMATA (CONTIN UED )—EURYPTERIDA Order II. Eurypterida. THE LEurypterida or Gigantostraca are found only in the Palaeozoic formations. Some species of Pterygotus, Slimonia, -and Stylonurus have a length of from five to six feet, and are not only the largest Invertebrates which have been found fossil but do not seem to be surpassed in size at the present day except by some of the Dibranchiate Cephalopods. All the Eurypterids were aquatic, and, with the possible exception of forms found in the Coal Measures, all were marine. The earliest examples occur in the Cambrian deposits, and the latest in the Permian ; but although the Eurypterids have thus a considerable geological range, yet it is mainly in the Silurian and the Old Red Sand- stone that they are found, the principal genera represented in those deposits being Lurypterus, Stylonurus, Slimonia, Pterygotus, Hughmilleria, Dolichopterus, and Husarcus. From the Cambrian rocks the only form recorded is Strabops;' in the Ordovician the imperfectly known Echinognathus* and some indeterminable fragments have alone been found, In the Carboniferous deposits Lurypterus and Glyptoscorpius occur, and the former survived into the Permian.’ 1 Walcott has described, under the generic name eltina, imperfect specimens from the Algonkian (pre-Cambrian) of Montana, which he thinks may be the remains of Eurypterids (Bull. Geol. Soc. America, x., 1899, p. 238). 2 Walcott, Amer. Jour. Sci. (5), xxiil., 1882, p. 213. ’ Descriptions and figures of British Eurypterids are given in the following works :—Huxley and Salter, ‘‘ Pterygotus,” Mem. Geol. Survey, Brit. Org. Re- mains, i., 1859; H. Woodward, ‘‘ Monograph of the Merostomata,” Palaeont. Soc. 283 284 ARACHNIDA—EURYPTERIDA CHAP. The Eurypterid which is best known is Lurypterus fischert (Figs. 161, 162), which is found in the Upper Silurian rocks at Rootzikiill in the Island of Oesel (Gulf of Riga). In the Fic. 161.—2Hurypterus fischeri, Eichw. Upper Silurian, Rootzikiill, Oesel. Dorsal surface. a, Ocellus ; }, lateral eye ; 2-6, appendages of prosoma ; 7-12, segments of mesosoma ; 13-18, segments of metasoma ; 19, tail-spine. (After Holm.) Eurypterids from other deposits the chitinous exoskeleton has been altered into a carbonaceous substance, but in the specimens from Oecesel the chitin is perfectly preserved in its original 1866-78, and Geol. Mag. 1879, p. 196; 1887, p. 481; 1888, p. 419; 1907, p. 277; Peach, Trans. Roy. Soc. Edinb. xxx., 1882, p. 511; Laurie, ibid. xxxvii., 1892, p- 151; xxxvii-, 1893, p. 509; and xxxix., 1899, p. 575. XI EXTERNAL FEATURES 285 condition; and since these specimens are found in a dolotnitic rock which is soluble in acid, it has been possible to separate the fossil completely from the rock in which it is embedded, with the result that the structure can be studied more easily and more thoroughly than in the case of specimens from other localities. Consequently Hurypterus fischeri’ may, with ad- vantage, be taken as a type of the Eurypterida. The general form of the body (Fig. 161) is somewhat like that of a Scorpion, but is relatively broader and shorter. On the surface of many parts of the exoskeleton numerous scale-like markings are found (Figs. 162, 163).° The prosoma or cephalo- thorax consists of six fused segments covered by a quadrate carapace with its front angles rounded. This bears on its dorsal surface two pairs of eyes—large kidney-shaped lateral eyes and median ocelli (Fig. 161, 6, a). The margin of the dorsal part of the carapace is bent underneath to form a rim which joins the ventral part of the carapace. On the ventral surface of the prosoma (Fig. 162) six pairs of appendages are seen, of which only the first pair (the chelicerae) are in front of the mouth. The chelicerae are small, and each consists of a basal joint and a chela, the latter being found parallel to the axis of the body ; they closely resemble the chelicerae of Limulus. The remaining five pairs of appendages are found at the sides of the elongate mouth, and in all these the gnathobases of the coxae are provided with teeth at their inner margins and were able to function in mastication, whilst the distal part of each appendage served as an organ of locomotion. The posterior part of each coxa is plate-like and is covered (except in the case of the sixth appendage) by the coxa of the next appendage ! A detailed account of Eurypterus fischeri has been given by G. Holm, Mém. Acad. Impér. Sci. St. Pétersbourg (8), viii. 2, 1898. See also F. Schmidt, ibid. (7), xxxi. 5, 1883. Descriptions of American forms of Hurypterus are given by Hall, ‘Nat. Hist. New York,” Palacont. iii., 1859, p. 395 ; ibid. vii., 1888, p. 156; and Second Geol. Survey Pennsylvania, ‘‘ Report of Progress,” ppp., 1884; Whiteaves, Geol. and Nat. Hist. Surv. Canada, ‘‘ Palaeozoic Foss,” iti., 1884, p. 42. 2 It was this ornamentation found on fragments of Pterygotus anglicus which led the Scotch quarrymen to apply the name ‘‘ Seraphim” to that Eurypterid. On this subject Hugh Miller writes: ‘‘ The workmen in the quarries in which they occur, finding form without body, and struck by the resemblance which the delicately waved scales bear to the sculptured markings on the wings of cherubs— of all subjects of the chisel the most common—fancifully termed them ‘Seraphim’ ” (The Old Red Sandstone, ed. 6, 1855, p. 180). 86 ARACHNIDA—EURYPTERIDA Fic. 162.—Eurypterus fischeri, Eichw. of ventral surface ; 1-6, appendages of prosoma ; m, metastoma. terior to the metastoma is the “median process”’ of the genital operculum. Holm. ) CHAP. Upper Silurian, Rootzikiill, Oesel. Restoration Immediately pos- (After XI APPENDAGES 287 behind. A small process or “ epicoxite” is found at the posterior end of the toothed part of the coxae of the second, third, fourth, and fifth pairs of appendages. The second appendage consists of seven joints, whilst the remaining four consist of eight joints; none of these appendages end in chelae. The second, third,’ and fourth pairs of appendages are similar to one another in structure, but become successively larger from before backwards. These three pairs are directed radially outwards; each consists of short joints tapering to the end of the limb, and bearing spines at the sides and on the under surface, and also a spine at the end of the last joint. The fifth appendage is longer than the fourth and is directed backwards ; its second and third joints are short and ring-like ; the others (fourth to eighth) are long and similar to one another, each being of uniform width throughout; the last joint is produced into a spine on each side, and between these two is the movable end-spine; the other joints do not bear long spines as is the case in the three preceding pairs of appendages. The sixth appendage is much larger and stronger than the others, and like the fifth, is without long spines. The coxa is large and quadrate; the second and third joints are short, like those of the fifth appendage; the fourth, fifth, and sixth joints are longer and more or less bell-shaped; the seventh and eighth joints are much larger than the others and are flattened. The metastoma (Fig. 162, m) is an oval plate immediately behind the mouth; it covers the inner parts of the coxae of the sixth pair of appendages, and represents the chilaria of Limulus. But, unhke the latter, it is not a paired structure; nevertheless the presence of a longitudinal groove on its anterior part renders probable the view that it is derived from a paired organ.? The front margin of the metastoma is indented and toothed. On its inner side in front is a transverse plate, the endostoma, which is not seen from the exterior, since the front margin of the metastoma extends a little beyond it. Behind the prosoma are twelve free segments, of which the 1 The third leg in the male possesses on the fifth joint a curved appendage which extends backwards to the proximal end of the second joint. This structure may have been a clasping organ. 2 It has been suggested that the metastoma really belongs to a_pre-genital segment of the mesosoma which is absent in the adult, but has been found in the embryo of Scorpions. 288 ARACHNIDA—EURYPTERIDA CHAP. first six form the mesosoma (Fig. 161, 7-12). The tergum on the dorsal surface of each segment is broad and short, the middle part being shghtly convex and the lateral parts shghtly concave ; the external margin is bent under, thus forming a narrow rim on the ventral surface. The tergum of each segment overlaps the one next behind. The segments increase in breadth slightly up to the fourth segment, posterior to which they gradually become narrower. . On the ventral surface the segments of the mesosoma bear pairs of plate-like appendages, each of which overlaps the one behind lke the tiles on a roof. On the posterior (or inner) surfaces of these appendages are found the lamellar branchiae, which are oval in outline (Fig. 165, d). Between the two appendages of the first pair is a median process which is genital in function; this pair are larger than the other appendages, and cover both first and second segments, the latter being without any appendages, and they represent the genital operculum of Limulus (Fig. 155, 10). The form of the operculum, more par- ticularly of the median process, differs in the male and female. In that which is believed to be the female (Fig. 162) the median process is long, and extends beyond the posterior margin of the operculum ; it is formed of two small five-sided parts at the base which are united at the sides to the two plates of the operculum ; behind this is a long, unpaired part, which is pointed in front ; this, together with the remaining parts, is not jomed to the side-plates of the operculum, so that the latter are here separated trom one another. The third part of the median process is shorter than the second, and bears at its end a pair of small pointed and diverging plates, the tips of which reach to the middle of the third plate-like appendages. On the inner side of the operculum there are, in the female, a pair of curved, tubular organs, attached to the anterior end of the median process, where they open, the free ends being closed; the function of these organs 1s not known, but was probably sexual. In the male (Fig. 163, A, a) the median process is formed of two parts only, and is very short, so that the two plates of the operculum unite behind the process. In the female a median process (Fig. 163, B) is also present between the second pair of appendages (belonging to the third segment of the mesosoma); it consists of a basal unpaired part, XI SEGMENTATION 289 and of a pair of long pointed pieces which project on to the next segment. Just as in the case of the genital operculum the basal part is united in front to the appendages, the remainder being free, and separating the greater part of the two plate-like append- ages. In the complete animal the median process of this segment is covered by the median process of the genital operculum. The remaining appendages of the female, and all the appendages behind the operculum in the male, are without any median Fic. 163.—Hurypterus fischeri, Kichw. Upper Silurian. (After Holm.) A, Genital operculum of male; a, median process. B, Middle part of second appendage of the mesosoma in the female, showing the median process. process, and the plates of each pair unite by a suture in the middle line. The metasoma (Fig. 161, 13-18) consists of six segments which become longer and narrower from before backwards. Each seoment is covered by a ring-like sheath or sclerite, and bears no appendages. The posterior end of the last segment is produced into a lobe on each side, and between these lobes the long, narrow tail-spine arises (Fig. 161, 19). | The other genera of the Eurypterida do not differ in any important morphological respects from the form just described, VOL. IV U 290 ARACHNIDA—-EURYPTERIDA CHAP. All the genera, of which about thirteen have been recognised, are placed in one family. Fam. Eurypteridae.—The carapace varies somewhat in out- line; in Slimonia it is more distinctly quadrate than in Fic. 164.— Pterygotus osiliensis, Schmidt, Upper Silurian, Rootzikiill, Oesel. Ventral surface. Reduced. (After Schmidt.) 1-6, Appendages of the prosoma; 7-12, mesosoma ; 7, 8, genital operculum ; 13-18, metasoma; 19, tail- plate ; a, epistome; 6, metastoma; c, coxae of sixth pair of appendages. Eurypterus, whilst im Pterygotus (Fig. 164) and Hughmilleria’ it is semi-ovoid. The lateral eyes are at the margin of the carapace in Ptery- gotus, Slimonia (Fig. 165, a), and Hughmilleria, but in the other genera, in- cluding the earliest form, Strabops, they are on the dorsal surface at a greater or less distance from the margin. The pre-oral append- ages of Pterygotus (Fig. 164, 1) differ from those of other genera in their much greater length and in the large size of the chelae; they probably consist of a proximal joint and chelae only, although, commonly, they are represented as having a larger number of joints. Unlike Hurypterus and Pterygotus, the second pair of appendages in Slimonia (Fig. 165, 2) differ from the third, fourth, and fifth pairs in being distinctly smaller and more slender, and it 1s probable that they were tactile. Whilst in Eurypterus the fifth pair of appendages are larger than the three preceding pairs, and also differ from them in 1 Sarle, New York State Museum, Bulletin 69, Palaeont. 9, 1903, p. 1087. 2 Beecher, Geol. Mag. 1901, p. 561. XI EXTERNAL FEATURES ZO structure, in the genus Prerygotus (Fig. 164, 5) they agree closely with the second, third, and fourth pairs, and in Slimonia (Fig. 165, 5) they are nearly the same as the third and fourth pairs. The sixth pair of appendages are much larger and more powerful than the. fifth pair in nearly all genera; in Stylon- urus (Fig. 166), however, the sixth pair are similar to the fifth, both being greatly elongated and slender; also in Husarcus (Drepanopterus) the sixth pair differ less from the preceding pair of appendages than is usually the case. In Pterygotus there is a well-developed epistome (Fig, 164, @) between the mouth and the front margin of the carapace, thus occupying the same position as the hypostome of Trilobites (p. 233). The metastoma is always well developed and forms one of the distinguishing features of the Eurypterids ; in form it varies from oval in Lurypterus, to cordate in Slimonia, and lyrate in Dolichopterus. The principal modifications seen in the genital operculum are in the form of its median process; in Slimonia this either ends in three sharp points posteriorly Ree Por hase the for fanny Fic. 165. — Slimonia acu- ( Ig. 9, ¢), Or has the torm or a trun- minata, Salter. Upper cated cone; its form in Hurypterus has Silurian. Restoration of elecad | dasteibed ce nae ventral surface, x 3. 1- already been described. Glyptoscorpius 6, Appendages. of. pro- differs from other Eurypterids in the — soma; 7, 8, genital oper- : , culum ; 7-12, mesosoma ; possession of comb-lke organs closely 13-18, segments of meta- resembling the pectines of Scorpions. Sm; 19, tail-spine ; «, ae aS we z lateral eye ; 6, metastoma, Slimonia apparently differs from other covering the inner parts genera in that the plate-like appendages °F, the coxae of the last 5 ‘ a pair of appendages ; cc, on the posterior three segments of the median process of genital 5 . eae : operculum ; d, branchial mesosoma do not meet in the middle line fee llesdeeriettinoribv the (Fig. 165, 10-12). In some forms, such plate-like appendages. é : After Laurie. as Pterygotus (Fig. 164), there is a nearly ee gradual decrease in the width of the segments in passing 292 ARACHNIDA—EURYPTERIDA CHAR. from the mesosoma to the metasoma; but in some others, which in this respect are less primitive, such as Slimonia (Fig. 165), the posterior five segments of the body (like those of Scorpions) are distinctly narrower and longer than the preced- ing segments. The long tail-spine of Hurypterus is represented in Slimonia by an oval plate produced into a spine at the end (Fig. 165, 19); whilst in some species of Pterygotus the plate is bilobed at the posterior end (Fig. 164, 19). In Hughmilleria the tail-spine is lanceolate. The Eurypterids resemble the Xiphosura in many respects. In both groups the prosoma consists of at least six fused segments, and bears two pairs of eyes—one pair simple, the other grouped eyes—on the dorsal surface of the carapace. The number and position of the appendages of the prosoma in Eurypterids agree with those of Limulus. The chelicerae are closely similar in both cases. The coxae of all five pairs of legs in Eurypterids are toothed and function in mastication ; similarly in Limulus all are spiny except the coxae of the last pair of legs. In both a similar epicoxite is present on the coxae. The number of joints in the legs 1s somewhat greater in the Eurypterids than in Limulus, and in the former none of the legs end in chelae, whereas in the latter all the walking legs, except the last, and also the first in the male, may be chelate. The metastoma of Eurypterids differs in being a large unpaired plate, but is represented in Limulus by the pair of relatively small chilaria. On the mesosoma the genital operculum and plate-like appendages with branchial lamellae are similar in both groups, but in the Eurypterids the genital operculum shows a greater development and covers the second segment, which is without plate-like appendages. A striking difference between the two groups is seen in the seg- ments of the mesosoma and metasoma; in Eurypterids these are all free, whilst in Zimulus they are fused together, but this difference is bridged over by some of the Palaeozoic Xiphosura (Fig. 159, A) in which those-segments are free. The Eurypterids present a striking resemblance to Scorpions. In both groups the segments in the three regions of the body are the same in number, and the appendages of the prosoma also agree in number and position. The pre-oral appendages are chelate in both, but the second pair of appendages are chelate in the Scorpions only. In Eurypterids the coxae of the five pairs XI EXTERNAL FEATURES Fic. 166.—Stylonurus lacoanus, Claypole. Upper Devonian, Pennsylvania. of dorsal surface. Length nearly five feet. (After Beecher. ) 293 Restoration 294 ARACHNIDA—EURYPTERIDA CHAP. XI of legs are toothed and meet in the middle line, but in the Scorpions the coxae of the last two pairs do not meet; this difference, however, appears to be bridged over in the earliest known Scorpion—Palaeophonus, from the Silurian rocks. The Eurypterids are distinguished from the Scorpions by the much greater development of the last pair of legs. The large meta- stoma of the former is homologous with the sternum of the Scorpion. The genital operculum is much smaller in Scorpions than in Eurypterids, and in this respect the latter agree with Thelyphonus (one of the Pedipalpi) more than with the Scorpions. The pectines are absent in the Eurypterids except in Glypto- scorpius. Instead of the lung-books of the Scorpions the Eurypterids possess branchial lamellae on the plate-like append- ages; but this difference between the two groups appears to be bridged over by Palaeophonus, which was marine, and may have possessed branchial lamellae since stigmata seem to be absent. Glyptoscorpius, which is found in the Lower Carboniferous of the south of Scotland, is a form of considerable interest. It is about a foot in length, and agrees in many respects with Eurypterida, but it may be necessary to separate it from that group since it possesses pectines, and the legs end in a double claw ; it cannot, however, be regarded as a link between Euryp- terids and Scorpions, but must rather be considered as an offshoot from the former, since the latter group was already in existence at a much earlier period. l Peach, Natwre, xxxi., 1885, p. 295; Pocock, Quart. Journ. Micr. Sct. xliv., 1901, p. 291; Laurie, Trans. Roy. Soc. Edinb. xxxix., 1899, p. 575. 2 Peach, Trans. Roy. Soc. Edinb. xxx., 1882, p, 516, ARACHNIDA EMBOLOBRANCHIATA (SCORPIONS, SPIDERS, MITES, Erc.) CECIL WARBURTON, M.A. Christ’s College, Cambridge ; Zoologist to the Royal Agricultural Society 4 Al # AO, Arby CHAPTER XI ARACHNIDA ( CON TIN UED )——EMBO LOBRANCHIATA—SCORPIONIDEA—— PEDIPALPI SUB-CLASS II—EMBOLOBRANCHIATA.’ Order I. Scorpionidea. Segmented Arachnids with chelate chelicerae and pedipalpr. The abdomen, which is broadly attached to the cephalothorax or prosoma, is divided into two regions, a sia-jointed mesosoma and a siz-jointed tail-like metasoma, ending in a poison-sting. There are four pairs of lung-books, and the second mesosomatic segment hears a patr of comb-like organs, the pectines. THE Scorpions include the largest tracheate Avachnid forms, and show in some respects a high grade of organisation. It is impossible, however, to arrange the Arachnida satisfactorily in an ascending series, for certain primitive characteristics are often most marked in those Orders which on other grounds would seem entitled to rank at the head of the group. Such a primitive characteristic is the very complete segmentation exhibited by the Scorpions. They are nocturnal animals of rapacious habit. In size they range from scarcely more than half an inch to eight inches in length. In the northern hemisphere they are not found above the fortieth parallel of latitude in the Old World, though in the New World they extend as high as the forty-fifth. A corresponding southward limit would practically include all the land in the southern hemisphere, and here the Order is universally represented except in New Zealand, South Patagonia, and the Antarctic islands. 1 Gf. p: 258: 297 2098 ARACHNIDA—EMBOLOBRANCHIATA CHAP. Fossil scorpions are rarely found. The earliest examples known occur in the Silurian rocks, and belong to the genus Palaeophonus. In the Carboniferous Hoscorpius is found, and in the Oligocene 7%tyus. Much remains to be discovered with regard to the habits of scorpions, and most of the isolated observations which have been recorded lose much of their value through the uncertainty as to the species concerned. The brief accounts given by Lankester and by Pocock,’ and the more recent and elaborate studies of Fabre,” are free from this defect and contain almost the only trust- worthy information we possess. All are viviparous, and the females carry the newly-hatched young on their backs. They are predaceous, feeding for the most part on insects and spiders. These are seized by the chelate pedipalps, and, if small, are simply picked to pieces by the chelicerae and devoured, but if large the tail-sting is brought into play and the victim quickly paralysed. The process of eating is a slow one, and a Cape scorpion in captivity took two hours to devour a cockroach. In walking, scorpions carry their pedipalps horizontally in front, using them partly as feelers and partly as raptorial organs. As regards the body the attitude varies considerably. In some cases (Parabuthus, Prionurus, etc.) it is raised high upon the legs, and the “ tail” or metasoma is curved forward over the back, but in others (Huscorpius) the body is held low, and the “ tail” is dragged along behind, the end only being slightly curled. In the day- time they hide away under wood or stone, or in pits which they dig in the sand. Parabuthus capensis was observed to dig a shallow pit by means of its second and third ambulatory legs, resting on its first and fourth legs aided by the chelae and the metasoma. Those that hide under wood are usually found clinging to their shelter ventral side uppermost. In captivity the creatures, though supplied with water, were never observed to drink ; indeed, they are characteristic inhabitants of arid steppes and parched wastes. Like most Arachnids they can endure prolonged abstinence from food. The only sense well developed seems to be that of touch. Notwithstanding the possession of several eyes their sight is 1 Nature, xlviii., 1893, p. 104. 2 Souvenirs entomologiques, Sér. 9, 1907, p. 229. XII SCORPIONIDEA—SCORPIONS 299 poor. A moving object within the range of a few inches is certainly perceived, but it has to be touched before its nature is recognised. Some writers have attributed to scorpions a keen sense of hearing, and so-called “auditory hairs” are described on the tibia of the pedipalp, but Pocock came to the conclusion that Parabuthus capensis and Euscorpius carpathicus were. entirely deaf, and Lankester could obtain no indication of auditory powers in the case of Prionurus. The sense of touch is extremely delicate, and seems to reside in the hairs with which the body and appendages are more or less thickly clothed. The pectines are special tactile organs. That they are in some way related to sex seems probable from the fact that they are larger in the male and sometimes curiously modified in the female, but they appear to be of use also in determining the nature of the ground traversed by the animal, being long in such species as raise the body high on the legs, and short in those that adopt a more grovelling posture. Pocock noticed that a scorpion which had walked over a portion of a cockroach far enough for the pectines to come in contact with it immedi- ately backed and ate it. As is the case with most poisonous animals, their ferocity has been much exaggerated; they never sting unless molested, and their chief anxiety is to slink off unobserved. The fables that they kill their young, and that when hard pressed they commit suicide by stinging themselves to death, perhaps hardly deserve serious con- sideration. The latter accusa- tion is disproved by the fact that a scorpion’s poison has no effect upon itself, or even upon a closely-allied species. Some writers think that in the frantic waving of the “tail,” which is_ generally induced by strong excitement, a scorpion may sometimes inadvertently wound itself with the sharp point of its telson. Fabre gives a fascinating account of the habits of Buthus occitanus, which occurs in the south of France. He found Fic. 167.—Buthus occitanus in the mating period, (After Fabre.) 300 ARACHNIDA—SCORPIONIDEA CHAP. these scorpions plentifully in arid, stony spots exposed to the sun. They were always solitary, and if two were found under the same stone, one was engaged in eating the other. Their sight is so poor that they do not recognise each other without absolute contact. Fabre established colonies in his garden and study, providing them with suitable soil and sheltering stones. They dug holes by reducing the earth to powder by means of the three anterior pairs of legs—never using their pedipalpi in the operation— and sweeping away the débris with the tail. From October to March they ate nothing, rejecting all food offered to them, though always awake and ready to resent disturbance. In April appetite seemed to awaken, though a very trifling amount of food seemed to suffice. At that time, too, they began to wander, and apparently without any intention of returning, and they continued daily to escape from the garden enclosure until the most stringent measures were taken to keep them in. Not till they were surrounded by glass and the framework of their cages covered with varnished paper were their attempts to climb out of their prison frustrated. Fabre came to the conclusion that they took at least five years to attain their full size. His most interesting observations were concerned with their mating habits, in connection with which he noted some extra- ordinary phenomena. After some very curious antics, in which the animals stood face to face (Fig. 167) with raised tails, which they We (SS => Z¢ intertwined — evidently v with no hostile inten- WINES tion—they always in- CAC Wes Vf if f{-7- ulged in what Fabre calls a “promenade a deux,” hand in hand, so to speak, the male seizing the chelae of the female with its own, and walking backwards, while the female followed, usually without any reluctance. This promenade occupied an hour or more, during which the animals turned several times. At length, if in the neighbourhood of a suitable stone, the male would dig a hole, without for a moment entirely quitting its hold of the female, Fic. 168.—The ‘‘ promenade a deux” of Buthus occitanus. (After Fabre.) XII HABITS—EXTERNAL STRUCTURE 301 and presently both would disappear into the newly-formed retreat. After mating, the male was often devoured by the female. Moreover, after any combat with an enemy, such as a Lycosa or a Scolopendra, it appeared to be de rigueur to eat the vanquished, and on such occasions only was any considerable amount of food consumed. The scorpions were not, however, anxious to fight, greatly preferring to retire if possible; but when incited to combat, their sting was quickly fatal to any mature insect, to spiders and to centipedes. Curiously enough, however, insect larvae, though badly wounded, did not succumb to the poison. Newly-hatched scorpions mounted on the mother’s back, where they remained motionless for a week, entirely unfed. They then underwent a moult, after which they were able to forage for themseives. External Structure. The chitinous plates of the prosoma are fused to form a carapace. Six segments are clearly indicated by the six pairs of appendages, but, though the development of Scorpio affords little direct evidence of the fact, there is reason to believe that there once existed a pre-cheliceral segment,’ as has been clearly proved in the case of the spiders. An embryonic pregenital segment has also been recognised. The six prosomatic appendages are those proper to the Arachnida, being the chelicerae, pedipalpi, and four pairs of ambulatory legs. ‘The mesosoma, which is broadly attached to the prosoma, comprises six segments, in- dicated ventrally by the genital operculum, the pectines, and the four pairs of pulmonary stigmata. The last of the broad ab- dominal segments, which tapers abruptly, belongs to the metasoma, which also comprises six segments, and is succeeded by the post-anal spine or sting. Prosoma.—Near the middle of the carapace are two median eyes, and on its antero-lateral borders are usually to be found groups of smaller eyes, numbering from two to five. All the eyes are simple. There is a difference, however, in their development, the median eyes being diplostichous, or involving two layers of hypoderm, while the lateral eyes are monostichous, and pass through a stage strikingly hke the permanent condition of the 1 Brauer, Zeitschr. wiss. Zool. lix., 1895, p. 355. 302 ARACH NIDA—SCORPIONIDEA CHAP. eyes of Limulus. The arrangement of various slight longi- tudinal ridges on the dorsal surface of the carapace is of systematic importance. On the ventral surface, just in front of the genital /] yy f NY and , - Pedipalp k Lateral eyes : [tie eyes (Z-° _-4 eS SF a pe: G ty _ _-SCE7RUM Prosoma } genital “operculum Pectines Mesosoma 7 SELGMALA R Metasoma aculeus. ‘vestcle Fia. 169.—Buthus occitanus. A, Dorsal view ; B, ventral view. (After Kraepelin. ) operculum, is a sternum, never large, and sometimes barely visible. Its shape and size constitute one of the principal family characteristics. Mesosoma.—The dorsal plates or terga are distinct, and are connected by soft chitin with their corresponding sterna. Beneath the second abdominal segments are borne the “pectines” or comb-like organs. In their structure four portions are distinguishable, an anterior lamella or shaft attach- ing them to the body, a middle lamella, the teeth, and the fulcra, a series of small chitinous pieces intercalated between the bases of the movable teeth. XII SEGMENTATION—-APPENDAGES 30 Oo Beneath the third, fourth, fifth, and sixth segments are the paired openings of the lung-sacs. Metasoma.—The first segment is usually and the remainder are invariably enclosed in complete chitinous rings and show considerable variations in their comparative size and shape, and in the arrangement of the ridges and keels with which they are usually furnished. The post-anal segment is more or less globular at its base, constituting a “vesicle,” and terminates in a fine curved point, the “aculeus,” perforated for the passage of the delicate poison-duct. With the abdomen fully extended the point is directed downward, but in the attitude of attack or defence, when the “tail” is carried horizontally over the back, the sting points forward in the neighbourhood of the animal’s head. Appendages.—The three-jointed chelicerae are powerful and chelate. The first joint is small, but the second is strongly developed and bears at its anterior end on the inner side a_pro- jection which forms the immovable finger of the chela. The third joint, or movable finger, is articulated on the outer side, and both fingers are armed with teeth whose arrangement is useful in distinguishing the species. The pedipalpi consist of six joints. The coxa is small and has an inwardly directed lamella which assists in feeding. The trochanter is also a small joint, bearing, normally at right angles to the longitudinal axis, the powerful humerus or femur. Then follows the brachium or tibia, again directed forward, and the last two joints form the chela or “hand,” the terminal joint or movable finger being on the outer side as in the chelicerae. In systematic determination special attention is given to the “hand.” In some forms the upper surface is uniformly rounded, while in others a “ finger- keel” divides it into two flattish surfaces almost at right angles. The biting edges of the fingers are usually furnished with rows of minute teeth arranged characteristically in the different genera. The ambulatory legs are seven-jointed, though, untor- tunately, authors are not agreed upon the nomenclature of the joints. Kraepelin ' names them coxa, trochanter, femur, tibia, and three-jointed tarsus, and Simon * agrees with him. Pocock’s names ° 1 Das Tierreich, 8. Lief., 1899, p. 4. 2 Arachnides de France, vii., 1879, p. 84. 3 Fauna of British India, ‘* Arachnida,’ 1900, p. 8. 304 ARACHNIDA—SCORPIONIDEA CHAP. are coxa, trochanter, femur, patella, tibia, protarsus, and tarsus, and it is certainly convenient that each joint should have a separate name, but it must be borne in mind that the tibia of different authors is not always the same joint. Special atten- tion must be directed to the three terminal joints, which furnish highly important characteristics. The tibia (n_ Pocock’s sense) 1s sometimes pro- 1, vided with a“ tibial spur ” at its lower distal ex- tremity. From the soft arthrodial membrane be- tween the protarsus and tarsus may proceed one Fie, 170A, Diagram of, «Scorpius lg}. or more dark-tipped claw- 5, tibia; 6, protarsus; 7, tarsus; p.s, pedal like spurs, the “ pedal spur; 4s, tibial spur. B, Fourth tarsus of , ae eo? » ese Palamnaeus swanvimerdami ; 1, lateral lobe. SpurE The terminal (After Pocock.) joint (tarsus of Pocock) is variously furnished with hairs and teeth, and always ends in a pair of well- developed movable claws beneath which a much reduced and sometimes almost obsolete third claw is distinguishable. The tarsus generally projects in a “claw-lobe” over the base of the superior claws, and sometimes lateral lobes are present. The first and second coxae have triangular maxillary lobes directed towards the mouth. The third and fourth coxae are fused together on each side, and those on one side are separated from those on the other by the sternum. In other respects the four pairs of legs are usually similar. B Internal Anatomy. The alimentary canal is a fairly uniform tube, nowhere greatly dilated. The very small mouth leads into a small suctorial chamber, and this is connected by a narrow oesophagus, which pierces the cerebral nerve-mass, with a slightly dilated portion which receives the ducts of the first pair of gastric xu ANATOMY 305 glands, often called salivary glands. The succeeding portion in the prosoma receives four or five more pairs of ducts from the well-developed gastric glands. In the rapidly narrowing first metasomatic segment the intestine receives one or two pairs of Malpighian tubes, and thence proceeds to the anus, situated ventrally in the last segment. The vascular system is of the usual Arachnid type, the heart being a seven-chambered dorsal longitudinal vessel lying in a pericardium, with which it communicates by seven pairs of valvular ostia. Lankester’ has demonstrated several pairs of superficial lateral veins connecting two deep-seated ventral venous trunks with the pericardium. The lung-books are, so to speak, pushed in to dilatations of these trunks, so that some of the lateral veins carry blood newly aerated by the lung-books directly to the pericardium. The nervous system is not greatly concentrated except in the prosoma, where there is a single ganglionic mass which innervates not only the whole prosoma but the mesosoma as far as the first and sometimes the second pair of lung-books. There are two mesosomatic ganglia, variously situated in different genera, and each metasomatic segment has its ganglion. The generative organs are more or less embedded in the gastric glands. There are two testes, each composed of a pair of intercommunicating tubules, and connected by a common vas deferens with the generative aperture, which is furnished with a double protrusible intromittent organ. A pair of vesiculae seminales and a pair of accessory glands are also present. The female possesses a single ovary, consisting of a median and two lateral tubules, all connected by cross branches. In addition to the external sclerites a free internal skeletal plate, situated in the prosoma between the alimentary canal and the nerve-cord, furnishes convenient fulera for muscular attach- ment. It is known as the “ endosternite.” Brauer” has made the most complete study of the develop- ment of Scorpio, and two of the most interesting of his conclusions may be mentioned here. He has shown the lung-books to be derived from gills borne on mesosomatic appendages. Moreover he found in the embryo five pairs of segmental ducts—in 1 Tr. Zool. Soc. Xi. part x., 1885, p. 373. 2 Zeitschr. wiss. Zool. lix., 1895, p. 351. VAOUE,, ANY x 306 ARACH NIDA—SCORPIONIDEA CHAP. segments 3-6 and 8—and demonstrated that those of segment 5 persisted, though without external aperture, as coxal glands, and those of segment 8 as the genital ducts. Classification. More than 350 species of scorpions have been described, but many of these are “doubtful,” and probably the number of known forms may be put at about 300. These are divided by Kraepelin’ into six families and fifty-six genera. The best indications of the family of a scorpion are to be found in the shape of the sternum, the armature of the tarsi, and the number of the lateral eyes, while assistance is also to be derived from the shape of the stigmata and of the pectines, and from the absence or presence of a spine beneath the aculeus. The six families are: Buthidae, Scorpionidae, Chaerilidae, Chactidae, Vejovidae, and Bothriuridae. Fam. 1. Buthidae.—Sternuwm small and generally triangular. Tibial spurs in the third and fourth legs. Generally a spur beneath the aculeus. Lateral eyes three to five in number. There are two sub-familes: BUTHINAE and CENTRURINAE. The BUTHINAE, which possess a tibial spur, comprise fourteen genera, most of them Old World forms. The principal genera are Buthus, which contains about 25 species, and Archisometrus with 20 species. One genus only, Ananteris, is South American, and it includes only a single species. The genus Uroplectes, with 16 species, is almost entirely African. The CENTRURINAE, without tibial spur, are New World scorpions, though Jsometrus europaeus (maculatus) is cosmopolitan. The principal genera are 7ityus with 30 species, Centrurus with 13, and Jsometrus with 6. Fam. 2. Scorpionidae.—Sternum broad and pentagonal, with sides approximately parallel. No tibial spur, but a single pedal spur. Crenerally three lateral eyes. Nearly a hundred species of Scorpionidae have been described, distributed among fifteen genera. The following sub-families are recognised : Diplocentrinae, Urodacinae, Scorpioninae, Hemi- scorpioninae, and Ischnurinae. 1 Das Tierreich, 8. Lief., 1899. X11 CLASSIFICATION 307 The DIPLOCENTRINAE have a spur under the aculeus. They form a small group of only eight species. The principal genus, Diplocentrus, is entirely Neotropical, but Nebo has a single Old World representative in Syria. The URODACINAE, with the single genus Uvodacus, are Australian scorpions. As in the next sub-family, there are rounded lobes on the tarsi, but there is only a single keel on the “tail,” and the lateral eyes are two in number. Six good and three doubtful species are recognised. The ScORPIONINAE are Asiatic and African forms, and are recognised by the tarsi having a large lobe on each side, by the convex upper surface of the “hand,” by the presence of two median keels on the “ tail,” and by the possession of three lateral eyes. Palamnaeus (Heterometrus) has sixteen species in the Indian region. ‘There are about thirty species of Opisthoph- thalmus, all natives of South Africa. Pandinus includes about ten species, but there are only two species of the type genus Scorpio, S. maurus and S. boehmet. The sub-family HEMISCORPIONINAE was formed for the reception of the single Arabian species Hemiscorpion lepturus. Its most striking characteristic is the cylindrical vesicle of the tail in the male. The IscHNURINAE differ from the Scorpioninae chiefly in the absence of the tarsal lobes, the presence of a well-marked finger- keel, and the generally more depressed form of the body and hand. In the opinion of some authors they should be separated from the Scorpionidae as a distinct family, the Ischnuridae. There are more than twenty species, divided among six genera. The type genus J/schnurus has only the single species £. ochropus. There are eight species of Opisthacanthus, which has representa- tives in Africa and America. Fam. 3. Chaerilidae.— Sternwm pentagonal with median depression or “sulcus” rounded posteriorly. Two pedal spurs. Stigmata circular. Two lateral eyes with a yellow spot behind the second. Pectines very short. This small family has the single genus Chaerilus with but seven species, natives of the Oriental region. Fam. 4. Chactidae.—7Zwo pedal spurs. Two lateral eyes (or, rarely, no eyes) but without yellow spot. Characteristic dentition on movable finger of “ hand.” 308 ARACHNIDA—-SCORPIONIDEA——PEDIPALPI CHAP. There are three sub-families, Megacorminae, Euscorpiinae, and Chactinae. The MeGAcoRMINAE include but a single Mexican form, Megacormus granosus. There is a single toothed keel under the “ tail,” and all the under surface is spiny. There is a row of long bristles under the tarsus. In the EuscorPlNag the upper surface of the hand is divided into two surfaces almost at right angles by a strong finger-keel. This is a small group of about six species found in the Mediter- ranean region. The two genera are Huscorpius and Lelisarius. The CHACTINAE are without any marked keel on the hand. The scorpions of this sub-family are found in equatorial South America and the West Indies, where there are more than twenty species divided about equally between the four genera Chactas, Broteas, Broteochactas, and Teuthraustes. Fam. 5. Vejovidae.—WNo tibial, but two pedal spurs. A single row of hairs or papillae under the tarsus. Sternum generally broader than long. Elongate stigmata, and three lateral eyes. Seven of the eight genera of this family include only American forms, the principal genus being Vejovis, with about ten species. The genus Scorpiops, however, belongs to the Indian region and numbers more than ten species.’ Fam. 6. Bothriuridae —Sternum much reduced and some- times hardly visible, consisting of two slight, nearly transverse bars. Of the seven genera of this family one, Cercophonius, is Australian. The other six genera include some dozen South American forms, Bothriwrus having four species. Order II. Pedipalpi. Arachnids with non-chelate, two-jointed chelicerae, powerful pedipalpt, and four pairs of legs, of which only the last three are ambulatory, the first being used as tactile organs. The cephalo- thorax is usually covered by an undivided carapace, but the pedun- culated abdomen is segmented. Respiration is by lung-books. The Pedipalpi are a little-known group of animals of nocturnal habits. Though rarely seen they are widely distributed, being found in India, Arabia, the greater part of Africa, and Central 1 Pocock, Fauna of British India, ‘‘ Arachnida.” London, 1900. XII EXTERNAL STRUCTURE 309 and South America. They are of ancient origin, a fossil genus, Gracophonus, of the Tarantulidae (Phrynidae, see p.3 12), occurring in the Carboniferous strata in North America. They hve under stones and bark, and in caves, where, when disturbed, they seek safety in crannies in the rock. Little is known of their habits, but they are believed to feed chiefly upon insects. The female 7arantula carries the developing egos, somewhat after the manner of the Chernetidea (see p. 454), in a bag beneath the abdomen, the under surface of which becomes concave and dome-like during the period of gestation.’ External Structure.— The external features which the members of this Order have in common are the segmented pediculate abdomen (9 to 12 segments), the two-jointed non-chelate chelicerae, the antenniform first pair of legs, and the presence of two pairs of lung-book stigmata beneath the abdomen. The constituent families differ ‘so much in outward form that they must be dealt with separately. The Thelyphonidae or “ Whip Scor- pions ” (see p. 312) have a long-oval cara- pace bearing well-developed eyes, two in front, and a group of three or five on either side some distance behind. The pedipalpi are chelate, and have their basal joints fused beneath the mouth, being thus incapable of any masticating motion. The first legs are six-jointed, and Fic. 171.—Thelyphonus, dia- have multi-articulate tarsi; the others are seven-jointed, and their tarsi, in some species at least, are tri-articulate. The abdomen consists of two portions, a wide nine-jointed pre-abdomen and a short narrow three-jointed post-abdomen, to which a filiform tail is articulated. grammatie ventral view ; about natural size. ¢, Coxal joint of pedipalp ; g, generative opening; Pp, pedipalp ; sp, spiracles ; st, sternal plates ; 1, 2, 3, 4, ambulatory legs. (After Pickard-Cambridge. ) Beneath the cephalothorax, between the coxae of the legs, is a distinct sternal plate in two portions (Fig. 171). developed, and covers two segments. The first abdominal ventral plate is largely Behind it are the median 1 Laurie, J. Linn. Soc. Zool. xxv., 1894, p. 30. 310 ARACHNIDA—PEDIPALPI CHAP. genital opening and two pulmonary stigmata, while the other stigmata are behind the second ventral plate, which corresponds to the third abdominal segment. On the last abdominal segment there are often two or four lght-coloured spots called “ommatoids,” and considered by some authors to be organs of sight. Laurie, however (vide infra), thinks it more probable that they are olfactory in function. The Schizonotidae (see p. 312) have a two-jointed carapace, and do not possess more than two eyes. There is a short unjointed tail-piece. In the Tarantulidae (Phrynidae) the whole body is much flattened and extended laterally, the undivided carapace being reniform,and broader than long. The long non-chelate pedipalps have their basal joints free and movable, and there are several sternal plates. There are nine abdominal tergal plates, the last three diminishing rapidly in size, and the last plate covering a button-lhke terminal portion of the abdomen. The first abdominal ventral plate is largely developed, as in the Thely- phonidae, and the genital orifice and pulmonary stigmata are in the same situation as in that group. The Tarantulidae have glutinous glands in the first abdominal segment which are capable of spinning a few irregular threads. In the whole group paired circular depressions are conspicuous dorsally on all the abdominal segments. These indicate the points of attachment of the dorso-ventral muscles. Internal Structure.—The anatomy of the Pedipalpi has been very inadequately studied. Disconnected notes on various points of structure have been published by various morphologists, but no complete investigation has yet been made of the internal organs. This is largely due to the difficulty of obtaining material, and the bad state of preservation of the internal parts of such specimens as have been available for dissection. The following points have been made out in the anatomy of Thelyphonus.' The alimentary canal commences after the mouth with a pharynx which, though not dilated, is furnished with sucking muscles. It then narrows into an oesophagus which passes through the nerve-mass, and afterwards dilates to form the mid- gut, which immediately gives off two large lateral diverticula 1 See M. Laurie in J. Linn. Soc. Zool. xxv., 1894, p. 20. XII ANATOMY Sy which extend backwards, each having five lobes. There are also two median diverticula which proceed from the ventral surface and pass through the endosternite. The abdominal portion of the canal is entirely concealed by the great “liver” mass which communicates with it by four paired ducts in the anterior part of the abdomen. Behind the fourth abdominal segment the gut is narrow till it expands in the seventh segment into an hour- glass-shaped stercoral pocket which, according to Laurie, is a portion of the mesenteron. The excretory organs are the Malpighian tubes and the coxal glands. The former are generally described as entering the anterior portion of the stercoral pocket, but according to Laurie they pass along its ventral surface, attached to it by connective tissue, and really enter at the posterior end. The coxal glands are well developed, and lie beneath the endosternite, opening near the first coxae. The nervous system is much concentrated and of the usual Arachnid type. The median abdominal nerve has a ganglion towards its extremity, supplying, according to Bernard,’ the muscles which move the tail. The heart is extremely long, and varies little in width. It has nine pairs of ostia “—two in the thorax and seven in the abdomen. The generative glands are paired, and in the male there are large seminal vesicles. In the most ventral portion of the abdominal cavity lies a remarkable asymmetrically-situated gland, the “stink-gland.” It consists of a number of secretory tubules communicating with two elongated sacs, one of which lies beneath the nerve-cord, and therefore medially, while the other les far to the left. Their ducts proceed to the anus or its vicinity. The caudal organs, or white spots which, as already mentioned, are usually found on the last of the three post-abdominal seg- ments of Vhelyphonus, are of doubtful function. They have been variously explained as the stink-gland orifices, and as organs sensitive to ight (“ommatoids”). Laurie® was unable to find any pore in this region, nor was there any of the pigment so characteristic of organs of sight. The histological structure indicated a sense-organ rather than a gland, but the use of these organs 1s entirely conjectural. 1 Tr. Linn. Soc. (2) vi., 1896, p. 344. 2 Bernard, lov. cit. p. 366. 3 J. Linn. Soc. xxv., 1894, p. 29. 312 ARACHNIDAS——PEDIPALPE CHAP. Classification. —The order Pedipalpi is divided into three families —Thelyphonidae, Schizonotidae and Tarantulidae. The first two are considered by some authors to form a sub-order, Uropyal, or tailed Pedipalpi, while the Tarantulidae constitute the remaining sub-order AMBLYPYGI, the members of which are tailless. Fam. 1. Thelyphonidae.’—This family comprises nine or more genera, differing chiefly in the position of the eyes, the structure of the genital operculum, the armature of the pedipalps, and the presence or absence of “ommatoids” in the anal segment. The three following genera are among those most likely to be met with. Two ommatoids are present in each. Thelyphonus has a spine on the second ventral plate, and a deep median impression on the male genital operculum, which is, however, absent from that of the female. There are about fifteen known species of this genus, inhabiting Southern Asia and the East Indies. Typopeltis has ridges running forward from the lateral eyes. The middle third of the female operculum is raised and deeply impressed in the middle. This genus is represented in China and Japan. Mastigoproctus has a short and stout coxal apophysis of the pedipalp, without a tooth on its inner side. It is found in Mexico, Brazil, and the West Indies. Other genera are Thelyphonellus (Demerara), Labochirus (Ceylon), Hypoctonus (Burma), imoscorpius (Philippines), Uroproctus (Assam), Abalius (New Guinea), without ommatoids, and Zetrabalius (Borneo), with two pairs of ommatoids. Fam. 2. Schizonotidae (= Tarcariduel —This family con- tains only two genera, Schizonotus (= Nyctalops, Pickard- Cambridge, nom. preoce. Aves) and Trithyreus” (= Tripeltis, Thorell, nom. preoce. Reptilia). They are very small, pale-coloured forms (about 5 mm. in length), found in Burma and Ceylon. Fam. 3. Tarantulidae, better known as _ Phrynidae. Pocock has shown that Fabricius established the genus Tarantula from the species 7. reniformis in 17938, while there is no earlier record of Olivier’s Phrynus, established for the same species, than Lamarck’s citation of it in 1801. The family is 1 See Pocock, Ann. Nat. Hist. (6), xiv., 1894, p. 120. * Kraepelin, Das Tierreich, Berlin, 8. Lief., 1899, p. 234. XII CLASSIFICATION divided into three sub-families, Tarantulinae, Phrynichinae, and Charontinae. (i.) The TARANTULINAE are new-world forms, represented by three genera, TZarantula, Acanthophrynus (Phrynopsis), and Admetus (Heterophrynus), 11 Central and South America and the West Indies. Ci.) The PHRYNICHINAE belong to the Old World, being found in Africa, India, and Ceylon. Phrynichus, Titanodamon and Nanodamon are genera of this sub-family. (ii.) The CHARONTINAE are natives of South-East Asia and the Pacific Islands. There are five genera and eight species. CEA PER, Xe ARACHNIDA EMBOLOBRANCHIATA (CONTINUED )—ARANEAE— EXTERNAL STRUCTURE—INTERNAL STRUCTURE. Order III. Araneae. (ARANEIDA,| ARANEINA.) Arachnida breathing by tracheae and “ lung-books.” Cephalo- thorax and pedicellate abdomen, the latter usually soft, and only very rarely showing any traces of segmentation. Two-jointed non- chelate chelicerae, the distal joint bearing the orifice of a poison- gland. The tarsal joint of the male pedipalp develops a sexual organ. The abdomen is furnished with spinning mammillae. THE true Spiders can readily be distinguished from allied Arachnid groups, with which they are often popularly confounded, by the presence of a narrow constriction or “waist” between the cephalothorax and abdomen, and of a group of “spinnerets ” or external spinning organs beneath the hind portion of the body, Thus the so-called “ Harvest-spider ” or “ Harvestman”’ is clearly not a Spider, for there is no constriction of its body into two parts, nor does it possess any spinnerets. It belongs to the Phalangidea. The same considerations will exclude the “ Red Spider ” of popular nomenclature, which must be referred to the Acarina or Mites. | The Araneae, even as at present known, form a very extensive and widely-distributed order of animals. Compared with certain insect orders, they have received little attention from the collector, bs ' The term mostly in use is Araneida, which should mean Araneus-like animals. This is clearly not allowable, unless there is a genus Araneus or Aranea. For many years there has been no such genus recognised, but Simon now attempts to re-establish it, inadmissibly, as it appears to us. (See note, p. 408). 314 CHAP. XIII - ARANEAE—SPIDERS 315 and the number of known forms is certain to be very largely increased. They form an extremely compact and natural group, for though, within the order, there is an infinite variety of detail, their uniformity in essential points of structure is remark- able, and they are sharply marked off from the neighbouring groups of Arachnida. It is perhaps unfortunate that the cbtrusiveness of particularly unattractive specimens of the race has always caused spiders to be regarded with more or less aversion. This prejudice can hardly fail to be modified by a wider acquaintance with these animals. There are certainly few groups which present points of greater interest in respect to their adaptation to special modes of life and the ingenuity displayed in the con- struction of their nests and the en- snaring of their prey. Spiders are wingless, yet they may often be observed travelling through the air. They are air-breathing, yet many are amphibious in their habits, pyc. 172.—Zpeira angulata. °. and one species at least spends the ereater part of its existence beneath the surface of the water. On land they may be found in all imaginable localities which admit of the existence of that insect life on which they depend for food. External Structure.—The spider’s body consists of two portions, the cephalothorax and the abdomen. Cephalothorax.—Looked at dorsally (Fig. 173), the cephalo- thorax is generally seen to have a depression near the middle, the “median fovea,” and from this certain lines, the “ radial striae,” radiate towards the sides. These depressions indicate the attach- ment of internal muscles. The head region or “caput ” lies in front of the foremost of the radial striae, and is often clearly marked off from the thorax, and different from it in elevation. It bears the eyes, which, in the great majority of spiders, are eight in: number. Many, how- ever, are six-eyed, while in rare cases the number is reduced to four (Tetrablemma, see p. 404), or even to two (ops, see p. 395). 316 ARACHNIDA—-ARANEAE CHAP. The number, relative size, and particular arrangement of these eyes are of considerable systematic importance. Their disposition varies very greatly, but it is generally possible to regard them as forming two transverse rows, an anterior and a posterior, each possessing a pair of median and a pair of lateral eyes. In many spiders all the eyes have a dorsal aspect, but in some groups (Attidae, Lycosidae) the prevailing arrangement is to have the anterior eyes directed forwards and the posterior upwards. In other spiders, again, a dorsal view may only show the eyes in profile, all having their axes directed forwards or sideways, or they may be mounted on turrets, and thus command a wide range of view. The rows are described as straight, “ procurved ” (with the convexity Fie sige pine nana backwards), or “recurved” (with the con- dorsal view ofaSpider. vexity forwards). Thus, in Fig. ee 7 ene chy, Chelioera 5 7) me anterior row /i8 slightly, and the posterior dian fovea ; , normal marking ; 0, ocular row considerably “ recurved.” a ans ene Sometimes there is a marked difference line should reach the jn the colour of the eyes, two or more being radial marking on the : 4 E cephalothorax. ) black, while the remainder are pearly white. In other cases they are homogeneous, either of the black or the white type. Simon considers the black eyes to be diurnal and the white nocturnal, but the evidence for this 1s indirect and not altogether satisfactory. The portion of the caput occupied by the eyes is often alluded to as the “ ocular area.” The space between the ocular area and the chelicerae, well shown in Fig. 177,is known as the “ clypeus.” It is usually more or less vertical, but in the Aviculariidae (see p. 386) it is horizontal and dorsal. The under surface of the cephalothorax is protected by the “sternum ” or “ plastron,” a large plate of variable shape, usually notched at either side for the reception of the legs, and having in front a small plate, generally hinged, but sometimes soldered to it, known as the “labium.” This has no homology with the labium of insects, but is a true sternite, more correctly described as “pars labialis sterni.” The labium and the maxillary lobes of the palpi more or less ch XII EXTERNAL FEATURES a7, conceal the under surface of the caput. The shape of the sternum and of the labium, and the contour and degree of inclination towards one another of the maxillae, are important considerations in the taxonomy of Spiders. The appendages of the cephalothorax, which are the chelicerae or jaws, the pedipalpi or feelers, and the four pairs of ambulatory legs, will be treated separately. Pedicle.-—The chitinous investment of the narrow stalk which unites the thorax with the abdomen is for the most part thin and flexible, with only slight indurations of various patterns on the dorsal surface, where it 1s in most cases more or less protected by the forwardly-projecting abdomen. Beneath, it is usually quite mem- 5. 4, eee branous, guarded only by a sort of collar formed matic ventral view by the raised border of the anterior portion of eee ite the abdomen at the point of insertion. In Labium; m, max- some Spiders, however (Dysderidae), there is a's" RK ie posterior sternal plate, the “plagula,’ closely — sternum; wu, un- aii 5 ¥s . : ‘guis of chelicera. corresponding with the labium in front, which — Ayaomen—a.t, partly embraces the pedicle. In Hermippus Sac (Zodariidae) the plagula is detached from the — gyne; 5, stigma; sternum, and is succeeded posteriorly by two __ spinnerets; ; tr, tracheal open- smaller paired plates. ing. Abdomen.— The abdomen differs remarkably in shape in the different groups of Spiders. In some families the prevailing shape is more or less globular, and in others cylindrical, while it may be diversified to almost any extent by prominences or spines. Ordinarily no sign of segmentation is observable, but in Liphistius it is covered dorsally by seven well-marked chitinous plates. In most Spiders the integument of the abdomen is uniformly soft and flexible all over, but it is not rare to find portions of it thickened and hardened to form “scuta.’ In the Gasteracan- thinae and the Phoroncidinae there is a great dorsal scutum armed with spines, while in several families there are species characterised by the possession of a smooth dorsal scutum ; and in some a ventral scutum is present. UW 318 ARACHNIDA—ARANEAE CHAP, That these scuta are sometimes indicative of an obsolete segmentation would seem likely from the study of the remarkable species, Tetrablemma mediocu- latum (Fig. 176), described by Pickard - Cambridge, — from Ceylon. In addition to large dorsal and ventral scuta, the sides and posterior extremity = are guarded by smaller scuta, the disposition of which is well seen in the figure. The normal smooth ab- ae domen presents dorsally no cane gs very striking features. In Fic. 175.—Spider profiles. 1, Poltys ideae; Species of variegated colora- 2, Phoroneidia 7-aculeata ; 35 Arvamnes tion there is very generally flagellum ; 4, Stegosoma testudo ; 5, For- i : ‘micinoides brasiliana. noticeable a median dentated band (Fig. 173), the “normal marking” of some writers, which would appear to have some correlation with the underlying dorsal vessel. Beneath the abdomen are to be seen the orifices of the breathing and genital organs, the spinnerets, and the anal aperture upon its tubercle. The breathing organs are, as will be explained later, of Fe. 176. — Tetrablemma medioculatum, much two kinds, lung-books and enlarged. A, Posterior view; B, profile, f ‘S) Pte showing the scuta. (After Cambridge.) tracheae. The great majority of Spiders possess only two lung-books, and their transverse, slit- like openings (“stigmata ” or “ spiracles”) may be seen on either side of the anterior part of the abdomen. Where, as in the Theraphosae, there are four lung-books, the second pair open by similar slits a short distance behind the first. According to Bertkau, pulmonary sacs are entirely lacking in the genus WVops. The tracheae generally debouch by a single median stigma towards the posterior end of the abdomen, just in front of the spinnerets. This opening clearly results from the fusion of two stigmata, which in some species retain their paired arrangement. On a level with the openings of the anterior lung-books or’ pulmonary sacs there is usually observable a shght transverse X11 APPENDAGES 319 ridge, the epigastric fold (Fig. 174), and in the centre of this is the genital opening. This is never visible until after the last moult, and in the male is always a simple inconspicuous aperture. This is also the case with the females of some groups (Theraphosae, Filistatidae, Dysderidae, etc.), but im most cases there is a more or less complicated armature, the “epigyne,” the special design of which is of great specific value. In its simplest form it is merely a plate, usually of dark colour, with one or two apertures (Fig. 174, ep), but in some families, notably the Epeiridae, it is more complicated, and is furnished with a hooked median pro- jection, the “ovipositor” (“clavus” of Menge), which is often absurdly like a petrified elephant’s trunk in miniature. The abdomen also presents on its under surface, usually to- wards the posterior end or apex, a group of finger-like mammillae or spinnerets. They are normally six in number, two superior (or posterior), two median, aud two inferior (or anterior). The number is reduced, in most of the Theraphosae, to four, while a few spiders possess only a single pair of spinnerets. These organs are described more fully on p. 325. A small papilla, the “colulus” (Fig. 174,c), is often observable, projecting between the anterior spinnerets. The “anal tubercle ” (Fig. 174, a7), on which the vent is situated, terminates the abdomen, and is generally in close juxtaposition with the posterior spinnerets. Appendages.—The cephalothoracic appendages are the cheli- cerae, the pedipalpi, and the four pairs of ambulatory legs. Those of the abdomen are the mammillae or spinnerets. Chelicerae.—These are two-jointed appendages, articulated immediately below or in front of the clypeus. They are the “mandibles” of many authors, but there is good reason for be- heving that they are not homologous with the mandibles of Insects. There is little agreement, moreover, with regard to the names given to the two joints of which they consist. The term “falx,” often applied to the basal joint, is much more appropriate to the sickle-like distal joint. Base and fang are tolerably satisfactory, or we may avoid ambiguity by adopting the terms “paturon” and “unguis” suggested by Lyonnet.! The paturon is a stout joint of more or less cylindrical or conical shape. The unguis (the “ crochet ” of Simon) is hook-like, 1 Mém. Mus. d’ Hist. Nat. xviii., 1829, p. 377. 320 ARACHNIDA——-ARANEAE CHAP. and can generally be folded back upon the paturon, which often presents a groove for its reception. The Theraphosid spiders are distinguished from all others by the fact that the plane of action of the chelicerae is vertical and longitudinal. The paturon pro- jects forward in a line parallel with the axis of the body, and its distal end can be raised or depressed, but not moved laterally ; while the unguis in action has the point directed downwards, and, at rest, is apphed to the under surface of the paturon. In other spiders the patura hang more or less vertically, and while to some extent mobile in all directions, their principal motion is lateral, and the ungues have their points directed to- wards each other in action, and are applied to the inner surfaces of the patura in repose. The plane of action in this case is also more or less vertical, but transverse. The paturon is always extremely hard and strong. In Thera- phosae of burrowing habits the distal end is furnished with a group of powerful teeth, the “rastellus.” The groove for the reception of the unguis is often guarded on one side or on both by rows of teeth, the arrangement of which is frequently an im- portant specific character. The inner anterior border is also often furnished with a group of stiff hairs or bristles. This powerful joint is : of use in crushing and expressing the fluids of 4 insects pierced by the ungues. Fig. 177. — Front view of Textrix denticulata. x about 10. ite Caput; 2, eyes; 3, paturon, and 4, unguis of cheli- cera. The crescent-shaped unguis is tapering and smooth, except for the presence, on the posterior surface, of one or two feebly dentated ridges. Near its free extremity there is a small orifice leading to the poison reservoir and gland. In the genus Pholcus(see p.401) the chelicerae may almost be regarded as chelate, the unguis being met by a spiny projection from the inner anterior border of the paturon. Rostrum.—On examining a spider, even under a dissecting microscope, it will not be easy at first to discover the mouth. Indeed, Lyonnet had almost come to the conclusion that Spiders, like some Myrmelionid larvae, imbibed the juices of their prey by way of the mandibles, before he found the orifice and gave a remarkably accurate description of the adjacent parts. If a specimen be placed on its back, and the labium raised XIII APPENDAGES 221 while the chelicerae are pushed forward, no orifice is visible, but on careful examination it will be found that what appears to be a thick and fleshy labium is, in reality, two organs. The labium is thin and flat, and closely opposed to its upper surface is ¢ somewhat flattened cone. This is the “rostrum,” and when it is separated from the labium the buccal orifice is disclosed. In a few spiders (Archeidae) in which the chelicerae are far removed from the mouth, the rostrum is tolerably conspicuous, but in most it is so hidden as to have escaped the observation of the great majority of observers. Schimkewitsch considers it homologous with the labrum of insects, but Simon thinks that it represents all the insect mouth-parts reduced to an exceed- ingly simple form. It is more probable that a beak consisting of a simple labrum and labium was a primitive Arachnid char- acteristic. If the rostrum be removed and its inner (or posterior) surface examined, a lance-shaped chitinous plate, the “ palate,” becomes visible. It is furrowed down the middle by a narrow groove, which is converted into a tube for the passage of fluids when the rostrum is opposed to the labium. Pedipalpi—tThe pedipalpi are extremely leg-like feelers, and are six-jointed, the metatarsal joint of the ambulatory legs being absent. The joints, there- fore, are the coxa, trochanter, femur, patella, tibia, and tarsus (Fig. 178). In the Theraphosae the coxa resembles that of the ambulatory leg, but in other QS spiders it is furnished, on the inner side, with a blade- like projection, the “ maxilla ” (Fig. 178). The shape of the maxillae and the degree of their inclination towards the labium are of considerable taxonomic importance. The inner border of the maxilla is furnished with a tuft of hairs, Fic. 178. —Pedipalp of Tegenuria domestica ¢ - x 5. 1, Coxa; 2, maxilla; 3, trochanter ; 4, femur; 5, patella; 6, tibia; 7, tarsus ; 8, palpal organ. ! Pickard-Cambridge (Spiders of Dorset, 1879-1881) omits the coxal joint, which, with its lobe, he calls the maxilla, and therefore gives only five joints, which he names axillary, humeral, cubital, radial, and digital. VOL. IV Me 322 ARACHNIDA—ARANEAE CHAP. which assist in retaining the juices expressed by the chelicerae, and its anterior border presents a cutting edge with a finely dentated ridge called the “ serrula.” In the female, and in the immature male, the remaining joints differ little from those of the legs, except that the tarsal joint is either clawless or has a single claw, which is generally smooth, and is never much dentated. At the last moult but one the male pedipalp appears tumid at the end, and after the last moult the tarsus is seen to have developed a remarkable copulatory apparatus, the “ palpal organ,” comparatively simple in some families, but in others presenting an extraordinary complexity of structure. Palpal Organs.— Externally the essential parts of the palpal organ are three, the “ haematodocha,” the “ bulb,” and the “ style.” The spines and projections, or “ apophyses,” which often accom- pany the palpal organ proper, are of secondary importance, and in many spiders are entirely absent; nor is their function when present at all clear; but the infinite variety of design which they ex- hibit, and their singular uniformity in all the males of a species, render them of the utmost value as specific characteristics. The “ haematodocha ” is the portion of the palpal organ attached to the tarsus, and often re- Fic. 179.—Diagram of palpal organ. 1, Tarsus ; ceived into an excavation, 2, bulb; 3, receptaculum seminis; 4, its aper- the “ alveolus,” Ons ture ; 5, style; 6, haematodocha; 7, alveolus ; . Siihie under surface. It is a fibro-elastic bag, in its normal collapsed state usually somewhat spirally disposed round the base of the following portion, the “ bulb.” The bulb is generally the most conspicuous portion of the organ, and is a sub-globular sac with firm, though often semi- transparent, integument. Its base rests upon the haematodocha, and its apex is produced, often spirally, to a point which bears the seminal orifice. This external opening leads into a coiled XUI APPENDAGES 323 tube within the bulb, ending in a blind sac, the “ receptaculum seminis,” which projects into the haematodocha; and it is the aperture by which the sperm both enters and leaves the organ. How the sperm is conveyed to the receptaculum was long a matter for speculation, after the belef in a direct communica- tion between the generative glands and the pedipalpi had been abandoned. The process has been actually observed in the case of a few spiders, which have been seen to deposit their sperm on a small web woven for the purpose, and then, inserting the styles of their palpal organs into the fluid, to suck it up into the receptacula seminis. This is probably the usual method of procedure, though it may be true, as some have asserted, that the palp is sometimes apphed directly to the genital orifice. The receptaculum and its tube bemg thus charged with sperm, it is the function of the haematodocha to eject it by exerting pressure on its base. For this purpose the haematodocha is in communication with the cavity of the tarsus, from which, in copulation, it receives a great flow of blood, and becomes greatly distended. Bertkau believes that he has detected very minute pores (meatus sanguinis) communicating between the haemato- docha and the receptaculum, and allowing some of the blood- plasma from the former to mingle with the semen, but this appears to be very doubtful. The Legs are uniformly eight in number, and are seven- jointed, the joints, counting from the body, being the coz, trochanter, femur, patella, tibia, metatarsus, and tarsus. In a few cases, through the presence of false articulations, 7.e. rings of softer chitin, this number appears to be exceeded. Some. of the Palpimanidae (see p. 398) were at first thought to have only six joints on their anterior legs, but the tarsus is present, though very small. In the case of most spiders, the legs take a general fore and aft direction, the first pair being directed forwards, the second forwards or laterally, and the third and fourth backwards. In the large group of “ Crab-spiders ” (Thomisidae), and in many of the Sparassinae, all the legs have a more or less lateral direction, and the spider moves with equal ease forwards, backwards, or sideways. The legs are usually more or less thickly clothed 1 Pickard-Cambridge, in his Spiders of Dorset, names them exinguinal, coxal, Femoral, genual, tibial, metatarsal, and tarsal. 324 ARACHNIDA——-ARANEAE CHAP. with hairs, but in some genera the clothing is so sparse that they appear glossy, while in others they have a positively shaggy appearance. Stouter hairs or “bristles” are often present, and some of the joints are also often furnished with “spines,” which in many cases are erectile. The tarsi of all spiders are furnished with terminal claws, usually three in number, though in some families (Drassidae, Thomisidae, etc.) there are only two. The two principal claws are paired and usually dentated, though the number of their teeth may be unequal. The third claw, when present, is always smaller, median, and inferior. In many spiders of climbing habits the place of the third claw is taken by a remarkable tuft of club-hke hairs termed a “scopula ” (Hig, 18055) by means of which they are able to cling to smooth surfaces where claws would be able to obtain no hold. In some species there is a special false articulation — the “onychium ”—at the end of the tarsus to bear the claws. In the Cribellatae the metatarsus is always fur- nished with a comb-like organ, the “calamistrum,” correlated with an extra spinning apparatus, the “eribellum,”’ but this will be dealt with when we reach the systematic Fic. 180.—Spider tarsi. 1, Tarsus of Apeira showing portion of the subject. three claws and supplemental serrate hairs (qa) ; F 3 2, tarsus of a Thomisid Spider, with two claws ; The general direction 3, 38a, lateral and dorsal view of tarsus of an _ a Dy ela ie : ) 7 ‘ e€ Attid Spider, showing scopula at 0. taken by the legs, th comparative length of the different joints, their armature of hairs, bristles, and spines, and the number and conformation of the tarsal claws, are points of great importance in the classification of Spiders. XIII SPINNERETS 325 Under considerable magnification the legs of all Spiders exhibit a number of minute organs, arranged with absolute uniformity throughout the Araneae,and known as the “lyriform organs.” They consist of little parallel ridges of thickened chitin, the sht between them being covered by thinner chitin. They are eleven on each leg, and are distributed near the distal extremities of each of the first six joints. Their function is unknown, though some authors consider them to be organs of hearing. The Spinnerets are normally six in number, and, except in rare instances, are placed beneath the abdomen, near its apex and immediately in front of the anal tubercle. Their arrangement varies greatly, but they can generally be recognised as comprising three pairs, a posterior (or superior) pair, a median pair, and an anterior (or inferior) pair. In nearly all the Theraphosae the anterior pair are absent, while the posterior spinnerets are largely de- veloped. In the Palpimanidae only the anterior spinnerets are present. When all six are found, the usual arrangement is in the form of a rosette, the median spinnerets being hidden by the others in repose, but this disposition is widely departed from. In Hahnia (Agelenidae), for instance, they are ranged in a transverse row at the end of the abdomen, the posterior spinnerets occupying the extremities of the row, and the median ones the centre. | These spinnerets are highly mobile TONSIL = spinnerels of Ween appendages, and additional play is given — diademata. A, Ventral view to their action by the presence of articula- Mea eh c B, eens J ag ; C, profile. tions, much resembling the “ false ” joints sometimes found on the legs, on the posterior and anterior pairs. They are always at least bi-articulate, and sometimes present three or four joints. They are movable turrets on which are mounted the “fusulae ” or projections where the tubes from the 326 ARACHNIDA—-ARANEAE CHAP. spinning glands open. These are often very numerous, especially in the orb-weaving spiders, where the spinning powers are most highly developed. They consist of two portions, a cylindrical or conical basal part, succeeded by a very fine, generally tapering tube. In some spiders the fusulae are all much alike, but usually a few very much larger than the rest are noticeable under the microscope, and these are often alluded to as “spigots.” The smaller ones are also divisible into two kinds, a few short conical fusulae being noticeable amongst the much more numerous cylindrical tubes. We shall treat of the functions of the various fusulae later (see pp. 335 and 349). Simon remarks that though the battery of fusulae is most complicated in those spiders which possess the greatest spinning powers, it is by no means among them that extremely long spinnerets are developed. The posterior spinnerets of some of the Hersiliidae are of great length, but these spiders spin very little except in forming their egg-cocoons. In addition to the six spinnerets, and just in front of them, there is to be found in some spiders an extra spinning organ in the form of a double sieve-like plate, the “cri- bellum.” ~~ his is always corre- lated with a comb of curved bristles on the metatarsi of the fourth pair of legs, the “cala- mistrum.” Such | importance 1s Fia. De TN Spinnerets of Amaurobius similis 2. Much assioned to these enlarged. «a, Anus; cr, cribellum; 7.s, inferior spinneret ; 2 m.s, median spinneret ; s.s, superior spinneret. B, Part of Organs by Sunon, the 4th leg of the same Spider, showing the calamistrum (ca) that the Araneae oh c C on the metatarsus. Veraeare divided by him according to whether they are present or absent, into CRIBELLATAE and EcRIBELLATAE. This is probably an exaggerated view of the importance of these organs, and the lor Cn BY i iy aaa XI STRIDULATING ORGANS 227 spiders possessing them certainly do not seem to form a natural group. Stridulating Organs—When Arthropod animals are capable of producing a sound, the result is nearly always obtained by “stridulation,” that is, by the friction of two rough surfaces against each other. The surfaces which are modified for this purpose form what is called a “stridulating organ.” Such organs have been found in three very distinct Spider families, the Theridiidae, the Sicariidae, and the Aviculariidae. Hitherto they have only been observed in three positions— either between the thorax and abdomen, or between the chelicerae and the pedipalpi, or between the pedipalpi and the first legs. In the Sicariidae and the Aviculariidae, the sounds have been distinctly heard and described. Those produced by the Theridiudae would appear to be inaudible to human ears. Westring’ was the first to discover (1843) a stridulating organ in the small Theridid spider Asagena phalerata. The abdomen, where the pedicle enters it, gives off a chitinous collar, which projects over the cephalothorax, and has the inner surface of the dorsal part finely toothed. When the abdomen is raised and depressed, these teeth scrape against a number of fine striae on the back of the posterior part of the ee ey: cephalothorax, A similar M™6,1857Strldvlatngs spperatue of aloe organ has been since found and toothed abdominal socket ; B, striated , area on the cephalothorax ; C, profile of the Spider, x 5. in various allied spiders, of which the commonest Eng- lish species is Steatoda bipunctata. In this group it is generally possessed by the male alone, being merely rudimentary, if present at all, in the female. In 1880 Campbell” observed that in some of the Theridiid Spiders of the genus Lephthyphantes, the outer surface of the 1 Nat. Hist. Tidsskr. iv., 1848, p. 349. oe imi SOCA SV grisly pe Lod. 328 ARACHNIDA-—ARANEAE CHAP. chelicera and the inner surface of the femur of the pedipalp were finely striated at the point, where they were rubbed together when the palps were agitated, but though the appropriate motion was frequently given, he could hear no sound. Meanwhile the noise produced by a large Thera- phosid spider in Assam (Chilobrachys — stridulans) had attracted attention, and its stridulating appa- ratus was described in 1875 by Wood-Mason.’ “The sound resembled that ob- tained by “drawing the back of a _ knife along the edge of a strong Fic. 184. — Chilobrachys stridulans in stridu- comb.” ie attitude. After Wood-Mason. Natural Subsequently certain Sicariid spiders of a genus confined to the southern hemisphere. were heard to produce a sound like the buzzing of a bee by the agitation of their palps, and both sexes were found to possess a very perfect stridulating organ, consisting of a row of short teeth on the femur of the pedipalp, and a striated area on the paturon of the chelicera. | Pocock has recently discovered that all the large kinds of Theraphosidae in the countries between India and New Zealand are, like Chilobrachys, provided with a stridulating organ. In these spiders also it is between the palp and the chelicera, and consists of a row of teeth or spines constituting a “pecten,” and a series of vibratile spines or “ lyra,” but whereas in Chilobrachys and its near relations the lyra is on the palp and the pecten on the paturon, in other spiders the positions are reversed. The lyra is a very remarkable organ, consisting of club-shaped, often feathery bristles or spines, which lie parallel to the surface to which they are attached, and which is slightly excavated for their reception. Lastly, many African Theraphosids possess a similar organ, 1 Proc. Asiat. Soc. Beng. 1875, p. 197. X1IT ALIMENTARY CANAL 329 not between the palp and the chelicera, but between the palp and the first leg. Various suggestions have been hazarded as to the use of these organs, but they partake largely of the nature of conjecture, especially in connexion with the doubt as to the possession of a true auditory organ by the Araneae. They may be summarised as follows. The Theridiid spiders are among those which show most indication of auditory powers, and the stridulating organs, being practically confined to the male, may have a sexual signifi- cance. Chilobrachys stridulates when attacked, assuming at the same time a “ terrifying attitude,” and its stridulating organ may serve the purpose attributed to the rattle of the rattlesnake, and warn its enemies that it is best let alone. If this be the case, there is no need that it should itself hear the sound, and, indeed, there is no evidence that the Avicularidae possess the power of hearing. In the inoffensive stridulating Sicarid spiders the sounds could hardly serve this purpose, and the presence of the organ in both sexes, and in immature examples, precludes the idea that its function is to utter a sexual call. Instead of trying to escape when disturbed, the spider starts stridulating, and Pocock suggests that the similarity of the sound produced to the buzzing of a bee may be calculated to induce its enemies to leave it in peace. Internal Anatomy. Alimentary System.—The alimentary canal of the Spider is divided into three regions, the “stomodaeum,” the mid-gut or “mesenteron,” and the hind-gut or “ proctodaeum.” The Stomodaeum consists of the pharynx, the oesophagus, and the sucking stomach, As we have said, the mouth is to be found between the rostrum and the labium. It opens into the pharynx, the anterior wall of which is formed by a chitinous plate on the inner surface of the rostrum, sometimes called the palate. As the inner surfaces of the rostrum and labium are practically flat, the cavity of the pharynx would be obliterated when they are pressed together, were it not for a groove running down the centre of the palate, which the apposed labium converts into a tube, up which the fluids of the prey are sucked. In the Thera- phosidae there is a corresponding groove on the inner surface of the labium. 330 ARACHNIDA—-ARANEAE CHAP. At the top of the pharynx, which is nearly perpendicular, the canal continues backwards and upwards as a narrow tube, the oesophagus, passing right through the nerve-mass, which embraces it closely on all sides, to the sucking stomach. At the com- mencement of the oesophagus is the opening of a gland, probably salivary, which is situated in the rostrum. We now reach the sucking stomach, which occupies the centre of the cephalothorax. It is placed directly over a skeletal plate, the “ endosternite ” (Fig. 185, ¢), to which its lower surface is connected by powerful muscles, while its upper wall is protected by a hard plate or “ buckler,” which is similarly attached to the roof of the cephalo- thorax in the region of the “ fovea media.” The walls of the stomach are not themselves muscular, but by the contraction of the muscles above mentioned its cavity 1s en- larged, and fluids from the pharynx are pumped up into it. The canal thus far is lined by chitin, hke the exterior of the Fig. 185.—Diagram showing the ana- body, and forms a sort of compli- tomy of the-cephalothorax of a cated mouth-apparatus. Spider. Theright alimentary diverti- culum has been removed. a, Aorta ; The Mesenteron lies partly in c, left diverticulum with secondary 1 caeca; e, endosternite: oes, oeso- the cephalothorax and partly in Phagus, descending to the mouth; the abdomen. The thoracic portion, s, sucking stomach ; sh, dorsal 3 : shield of sucking stomach. shortly behind the sucking stomach, sends forward on either side a large branch or “diverticulum,” from each of which five secondary branches or “caeca” are given off (Fig. 185). Of these the anterior pair sometimes join, thus forming a complete ring; but usually, though adjacent, they remain distinct. The other four pairs of caeca curve downwards, protruding into the coxae of the legs, where they often terminate, but sometimes (Hpei7a) they con- tinue their curve until they meet, though they never fuse, under the nerve-mass. Behind the origin of the diverticula the mesenteron continues as a widish tube, and shortly passes through the pedicle and enters the abdomen, where, curving slightly upwards, it pro- ceeds along the middle line till it ends in the proctodaeum. XIII VASCULAR SYSTEM BS In the abdomen it is surrounded by a large gland, the so- called liver, and is dilated at one spot (Fig. 186) to receive the ducts from this gland. The fluid elaborated by this large abdominal gland has been shown to have more affinity with pancreatic juice than with bile. The Proctodaeum consists of a short rectum, from the dorsal side of which protrudes a large sac, the “stercoral pocket.” At its origin, the rectum receives the openings of two lateral tubes which reach it after ramifying in the substance of the liver. These have been called “ Malpighian tubules,” but their function is unknown. Loman’ has shown that they open into the mid- eut and not into the rectum, and there is reason to believe that true Malpighian tubules homologous to those of Insecta are absent in Arachnida, where their place seems to be taken by the coxal glands, which are considered to be the true excretory organs. In most spiders they open near the third coxae. Like the stomodaeum, the proctodaeum has a chitinous lining. Vascular System.—The earlier investigations on the circula- tion of the blood in Spiders were made by direct observations of the movements of the blood corpuscles through the more or less transparent integuments of the newly hatched young. Claparéde’s ° results were arrived at by this method. It is invaluable for demonstrating roughly the course taken by the blood, but in these immature spiders the blood-system has not attained its full com- plexity, and other methods of research have shown the spider to possess a much more elaborate vascular system than was at first suspected. The tubular heart lies along the middle line in the anterior two-thirds of the abdomen, sometimes close up against the dorsal wall, but occasionally at some little distance from it, buried in the substance of the liver. It is a muscular tube with three pairs of lateral openings or “ ostia,” each furnished with a simple valve which allows the entrance, but prevents the exit, of the blood. It is contained in a bag, the “ pericardium,” into which the ostia open. Both heart and pericardium are kept in place by a complicated system of connective tissue strands, by which they are anchored to the dorsal wall of the abdomen. Eight 1 Tijdschr. v. d. Nederl. Dierkundige Ver. (2), i., 1885-1887, p. 109. 2 Etudes sur la circulation du sang chez les Aranées du genre Lycose. Utrecht, 1862. bo ARACH NIDA—ARANEAE CHAP. WwW Los) arteries leave the heart, the principal one, or “aorta,” plunging downward and passing through the pedicle to supply the cephalo- thorax. Besides this, there is a caudal artery at the posterior end, and three pairs of abdominal arteries, which proceed from the under surface of the heart, and the ramifications of which supply, in a very complete manner, the various organs of the abdomen. The heart is not divided up into compartments. The anterior aorta passes through the pedicle, above the intestine, and presently forks into two main branches, which run along either side of the sucking stomach, near the front of which they bend os 4 WW Wolly Wms sa CY ’ , g oe ESSTIFITG TT RPCOIES O55 eirewe eR ORE. a <5) ' 17 Fic. 186.—Diagram of a Spider, Lpeira diademata, showing the arrangement of the internal organs, x about 8. 1, Mouth; 2, sucking stomach ; 3, ducts of liver ; 4, so-called Malpighian tubules ; 5, stercoral pocket ; Me anus ; 7, dorsal muscle of sucking stomach ; 8, caecal pr olongation of stomach ; 9, cerebral ganglion giving off nerves to eyes; 10, sub-oesophageal ganglionic mass ; 11, heart with three lateral openings or ostia ; 12, lung-sac ; 13, ovary ; 14, acinate and pyriform silk-glands ; 15, tubuliform silk-gland ; 16, ampulliform silk-gland ; 17, aggregate or slusinerarn silk-glands ; ; 18, spinnerets or mammillae ; 19, distal jot of “chelicera : 20, poison- gland ; 21, eye; 22, pericardium ; 23, vessel bringing blood from lung-sac’ to peri- cardium ; 24, artery. suddenly downwards and end in a “ patte d’oie,” as Causard ? expresses i1t—a bundle of arteries which proceed to the limbs (Fig. 185). Where the downward curve begins, a considerable artery, the mandibulo-cephalic, runs forward to supply the cheli- cerae and the head region. We have omitted certain minor branches from the main trunks which supply the thoracic muscles. The nerve-mass receives fine vessels from the “ patte d’oie.” There are no capillaries, but the blood is delivered into the tissues and finds its way, by irregular spaces or “lacunae,” into certain main venous channels or “ sinuses.” There are three such 1 Recherches sur Vappareil circulatoire des Aranéides. Lille, 1896. X11 REPRODUCTIVE AND NERVOUS SYSTEMS 343 in the cephalothorax, one median and the others lateral, con- siderably dilated in front, in the region of the eyes, and connected by transverse passages. By these the blood is brought back through the pedicle to the lung-books. In the abdomen also there are three main sinuses, two parallel to one another near the lower surface, and one peneath the pericardium. These likewise bring the blood to the lung-books, whence it is conducted finally by pulmonary veins (Fig. 186) back to the pericardial chamber, and thus, by the ostia, to the heart. The Spider’s blood is colourless, and the majority of the corpuscles are “ amoeboid,” or capable of changing their shape. Generative System. The internal generative organs present no great complexity, consisting, in the male, of a pair of testes lying beneath the liver, and connected by convoluted tubes, the “vasa deferentia,” with a simple aperture under the abdomen, between the anterior stigmata. The ovaries are hollow sacs with short oviducts which presently dilate to form chambers called “ spermathecae,” which open to the exterior by distinct ducts, thus forming a double orifice, fortified by an external structure already alluded to as the “epigyne.” The eges project from the outer surface of the ovary like beads, connected with the gland by narrow stalks, and it was not at first clear how they found their way into the interior cavity, but it has been ascertained that, when ripe, they pass through these stalks, the empty capsules never presenting any external rupture. The palpal organs have already been described. The sperma- tozoa, when received by them, are not perfectly elaborated, but are contained in httle globular packets known as “ spermato- phores.” Nervous System.—The Spider's central nervous system is entirely concentrated in the cephalothorax, near its floor, and presents the appearance of a single mass, penetrated by the oesophagus. It may, however, be divided into a pre-oesophageal portion or brain, and a post-oesophageal or thoracic portion. The brain supplies nerves to the eyes and chelicerae, while from the thoracic mass nerves proceed to the other appendages, and through the pedicle to the abdomen. The walls of the oesophagus are closely invested on all sides by the nerve-sheath or neurilemma. Sense Organs.—‘Spiders possess the senses of sight, smell, and 334 ARACHNIDA—ARANEAE CHAP, touch. Whether or not they have a true auditory sense is still a matter of doubt. Since sounds are conveyed by vibrations of the air, 1t is never very easy to determine whether responses to sounds produced near the animal experimented upon are proofs of the existence of an auditory organ, or whether they are only per- ceived through the ordinary channels of touch. In any case, the organs of hearing and of smell have not yet been located in the Spider. _M‘Cook considers various hairs scattered over the body of the spider to be olfactory, but from Gaskell’s researches upon allied Arachnid groups it would seem that the true smelling organ is to be sought for in the rostrum. Eyes.—Spiders possess from two to eight simple eyes, the external appearance and arrangement of which have already been briefly explained. They are sessile and immovable, though often so placed as to command a view in several directions. In structure they are essentially like the ocelli of Insects. Externally there is a lens, succeeded by a mass of transparent cells, behind which is a layer of pigment. Then come the rods and cones of the retina, to which the optic nerve is distributed. A comparison of this with the arrangement in the Vertebrate eye will show a reversal of the positions of the retina and the pigment-layer. The lens is part of the outside covering of the animal, and is cast at the time of moulting, when the spider is temporarily blind. It is stated, however, that the eyes do not all moult simultaneously. There is often a considerable difference between the various eyes of the same spider, especially with regard to the convexity of the lens and the number of rods and cones. Though most spiders possess eight eyes, the number is some- times smaller, and in some groups of eight-eyed spiders two of the eyes are sometimes so reduced and degenerate as to be prac- tically rudimentary. As might be expected, Cave-spiders (e.g. Anthrobia mammouthia) may be entirely sightless. Touch.—The sense of touch would appear to be extremely well developed in some spiders, and there is reason for believing that the Orb-weavers, at all events, depend far more upon it than upon that of sight. Among the hairs which are distributed over the spider’s body and limbs, several different forms may be distinguished, and some of them are undoubtedly very delicate sense-organs of probably tactile function. , >| XIV EFFECTS OF POISON 363 terror which is locally inspired by the first-named species, whose bite is believed to be fatal unless measures are promptly taken to counteract the poison. They sometimes cauterise the wound, but the usual treatment consists in inducing profuse perspiration ——a method of cure which recalls the Tarantula dance of Southern Europe. Flacourt * mentions the Vancoho as the most dangerous animal of Madagascar, and more formidable than the scorpion. He relates cases among his own negroes where the bite was followed by a condition of syncope which lasted two days. A New Zealand species is known by the natives as the Aatzpo. It is of about the size of a pea, and almost black in colour. Mr. Meek of Waiwera gives a most circumstantial account of the effect of its bite upon his son.”, During the four days which followed the bite he suffered excruciating pain, which spread from his leg to the spine, arms, and chest, and he lost twelve pounds in weight. Relief was obtaimed by frequent doses of brandy and the use of a liniment. The natives of New Zealand have a great horror of this spider, but hold the curious belief that its death will ensure the cure of any one it may have bitten. If unable to find it, they will burn the house down rather than allow it to escape. Their dread, however, is confined to a variety which lives among the sedge of the sea-beach, and they carefully avoid sleeping in such places. Two of the best authenticated cases of serious results ensuing from the bite of a spider of this genus come from North Carolina.’ A farm labourer in the employ of Mr. John Dick of Greens- borough was bitten by Latrodectus mactans about half-past eight in the morning, and died between ten and eleven o’clock at night. Small pimples were raised in the neighbourhood of the bite, but no puncture was discernible. Intermittent pains and spasms ended in a comatose condition from which he did not rally. The man appeared previously to be in perfect health. Another man on Mr. Dick’s farm was bitten by the same species of spider. He resumed work, but a spasm of pain caused him to mount his horse and endeavour to ride home, but he fell off, and lay in a state of unconsciousness. He was found in this condition by a fellow-workman, and taken home. Large quantities l Hist. de la grande tle de Madagascar, 1658, p. 156. 2 Science Gossip, 1877, p. 46. 3 Insect Life, i., 1889, p. 205. 364 ARACHNIDA—ARANEAE cna. of whisky were administered without any intoxicating effect, and this afforded some relief from the constantly-recurring spasms. The paroxysms continued for three weeks, and two months elapsed before he was able to resume work. On the ankle where he was bitten pimples appeared as in the previous case, and these broke out again, long after the occurrence, whenever he became over- heated in his work.’ These accounts are sufficiently circumstantial and well authen- ticated, but the fact of the actual bite depends upon the state- ment of the victims alone, and they may possibly have mistaken the cause of their trouble. Southern Europe possesses a congener of this spider in Latrodectus 15-guttatus, the well-known “ Malmignatte,”’ which is also considered extremely poisonous. The Royal Academy of Medicine and Surgery at Barcelona appointed Dr. Graells, in 1835, to inquire into the effects of the bite of this spider, cases of which had become exceedingly-frequent. He found a curious correspondence between the frequency of these cases and -the advent of migratory locusts, which the spider successfully attacked. In his report! he details the symptoms in certain unquestionably authentic cases. There was a double puncture, surrounded by red circles, the region of the wound afterwards swelling greatly. The pain and swelling extended over the whole limb, and often to the body, and convulsions occurred, followed by great prostration and collapse. All the patients eventually recovered, their cure being heralded by profuse perspiration. It must be mentioned, however, that the eminent Arachnologist M. Lucas states that he has several times allowed himself to be bitten by this identical spider without any ill effects. The testimony is thus conflicting in this case also. It is impossible, however, to believe that there is no basis in fact for the poisonous reputation of a comparatively insignificant-looking spider in so many widely-separated parts of the world, supported as it 1s by certain well-substantiated cases. The variable effects of its bite may find a partial explanation in a variation in the strength of its venom at different seasons, and it has already been mentioned that the injection of poison into its victim is a voluntary act, and does not necessarily accompany its bite. Among the 1 Ann. Soc. ent. France, xi., 1842, p. 205. Translated from the Spanish by L. Fairmaire. XIV _ POISON—FERTILITY 365 species regarded as especially venomous must be mentioned Phidippus morsitans, one of the larger of the Attidae. It is exceedingly likely that the bite of the large tropical Aviculariidae is really formidable. They appear, however, more anxious to escape than to show fight, and we possess lttle reliable information with regard to them. Doleschall shut up small birds with two West Indian species, and death followed their bite almost immediately. Ten days’ starvation appeared to weaken the venom, for a bird bitten by a spider fasting for that period recovered after an indisposition of six hours. Most Arachnologists have recorded experiments with regard to the venom of the commoner European species, with equally con- flicting results. Blackwall came to the conclusion that loss of blood, and not poison, caused the death of spider-bitten insects. He could not himself distinguish a spider bite from the prick of a needle inflicted upon his hand at the same time. Bees, wasps, and grasshoppers survived the bite about as long as other insects of the same species outlived a needle-prick in the same part of the body. Walckenaer’s experience was of the same nature. Bertkau, however, when bitten in the hand, felt clear indications of an irritant poison in the wound. The hairs of some of the large hairy species of the Aviculariidae possess poisonous properties. They are readily parted with, and when the animal is touched by the hand considerable irritation is set up. Fertility of Spiders.—Spiders vary greatly in the average number of eggs laid by different species, and within the limits of each species there is a very considerable variation in fertility. As a rule it appears that the large and vigorous spiders are more prolific than the smaller and weaker members of the order. Were all the facts before us, however, we should no doubt find that the number of eggs laid bore a direct proportion, not to the size of the species, but to the dangers to which the young of that species are exposed. Where the total numerical strength of a species is fairly stationary, such a proportion must of course exist. Some species, no doubt, are tending to become extinct, while others are increasing in numerical importance. As a general rule, however, it is safe to infer that, if a species is especially prolific, special dangers attend the rearing of the young. The largest of North American Epeirids, Argiope cophinaria,’ 1 M‘Cook, American Spiders and their Spinning Work, ii., 1890, p. 188. 366 ARACHNIDA—ARANEAE CHAP. constructs a cocoon containing, on an average, 1150 eggs. As many as 2200 have been counted in exceptional cases. Even this number is exceeded in the case of some of the great Aviculariidae. Theraphosa leblondi deposits as many as 3000 egos. The large European Epeirids, 2. quadrata and #. diademata, lay about 600 eggs, those of Lycosa narbonensis reaching about the same number. Those American spiders which have been described as stringing up a series of cocoons in their webs usually attain about the same aggregate, the eggs being less numerous in each cocoon. These are examples of fairly large and fertile spiders. In the case of other species the number of eggs laid is exceedingly small. Ero furcata makes a single cocoon containing six eggs. Synageles pieata, an ant-like Attid, lays only three. Oonops pulcher con- structs several cocoons, but each contains only two eggs. The egos of Cave-spiders, and such as live in dark and damp places, are generally few in number. ). The burrow is sometimes simple and sometimes branched, and the trap-door may be either thin, or thick with bevelled edges. Allied genera are Hermacha and Rachias in South America, Spiroctenus in South Africa, Genysa in Madagascar, Scalidognathus in Ceylon, and Arbanitis in New Zealand. The genus Cteniza (fovea procurved ~) possesses only a single species (C. sawvaget), found in South-East France and Italy. Pachylomerus is a widely-distributed genus, being represented in North and South America, Japan, and North Africa. The tibiae of the third pair of legs are marked above by a deep impression near the base. A closely allied genus, Conothele, inhabits Southern Asia and New Guinea. The widely-distributed genus Acanthodon, which has repre- sentatives in all the sub-tropical countries of the world, together with the South American genera /diops and Pseudidiops, and the Indian genus Heligmonerus, present a peculiar arrangement of the eyes, one pair being situated close together in the middle of the front of the caput, while the remaining six form a more or less compact group some distance behind them. Among the many other genera of the Ctenizinae may be mentioned Cyrtauchenius, of which many species inhabit North- West Africa, and its close ally Amblyocarenum, represented on both shores of the Mediterranean, and in North and South America. They differ from Cteniza chiefly in the possession of strong scopulae on the tarsi and metatarsi of the first pair of legs, and in the double row of teeth with which the tarsal claws are furnished. XV AVICULARIIDAE 389 Their burrows are often surmounted by a sort of turret raised above the level of the ground. (v.) The BARYCHELINAE are burrowing forms which resemble Nemesia, but have only two tarsal claws. Leptopelma is the only European genus, and has close affinities with certain South American genera (Psalistops, Huthycoelus, etc.). Pisenor inhabits tropical Africa, and Diplothele, unique in possessing only two spinning mammillae, is an inhabitant of India. (vi.) The AVICULARIINAE include all the large hairy spiders which are commonly called Mygale. The genus Phlogius, which inhabits Southern Asia, forms a lidless burrow, though it has no rastellus, but practically all the other members of the group are non-terricolous, ving under stones or in holes in trees, where they weave a slight web. They are nocturnal in their habits. They all possess two tarsal claws, and the labium is free and spined at the tip. Of the four spinnerets the posterior pair are long and three-jointed, while the anterior are short and not very close together. The particular form of the tarsi and the nature of the scopulae,' “ claw-tufts,” and spines upon them are of great import- ance in distinguishing the members of this group. The Aviculariinae comprise about sixty genera from all the tropical and sub-tropical regions of the world. The genus J/schnocolus extends into the Mediterranean region, having representatives besides in Southern Asia and in Central and South America. Allthe tarsi have their scopulae divided longitudin- ally by a band of hairs. Chaetopelma inhabits Egypt, Syria, and Arabia, and Cyclosternum is found in West Africa as well as in Central and South America. In these genera the scopulae of the last two pairs of legs are alone divided. The largest known spider is Theraphosa leblondi, which is a native of Guiana. It measures 9 cm. (about three and a half inches) in length. Eurypelma is a genus of large spiders entirely confined to the New World, where it possesses many species. The genus Avicularia is also American, and includes a number of large long-haired spiders with short and very strong legs, on which The ‘‘scopula”’ is the pad of close-set thick hairs whieh covers the under surface of the tarsus and often of the metatarsus. The ‘‘ claw-tufts” are groups of longer hairs, often extending beyond the claws, and giving the foot a bifid appear- ance. 390 ARACHNIDA—ARANEAE CHAP, the scopulae and claw-tufts are well developed. Its nearest allies in the Old World are the Indian genus Poecilotheria, and the West African genus Scodra. The stridulating spider figured on p- 328 belongs to this group, Chilobrachys being a genus from Ceylon. (vu.) The DipLURINAE are a very aberrant group, including some twenty genera of Aviculariidae, usually of medium size, and possessed, as a rule, of very long posterior spinnerets. They do not burrow or live in holes or under stones, but weave webs of close texture, much resembling those characteristic of the Agelenidae (see p. 415). The tarsal claws are three in number, and there are never any claw- tufts. The rastellus, of course, is absent. Two genera have representatives in Europe, Brachythele inhabiting the East aie DN Gade Mediterranean region (as well as many aye et “other parts of the world), while Macrothele is found in Spain as well as in the Malay Peninsula and New Zealand. Ischnothele dumicola is a native of Western India. Diplura is a South American genus. Tvrechona venosa, a large species remarkable for the orange bands which decorate its abdomen, is also a native of South America. The New Zealand genus Hexathele, and the genus Scotinoecus from Chili, possess six spinnerets. MJasteria (Ovalan Island) and Accola (Philippines and South America) differ from the rest of the family in having only six eyes. Fam. 3. Atypidae.—Spiders with anteriorly projecting and vertically articulating chelicerae, but with no trough on the paturon for the reception of the unguis, which is guarded when closed by a single row of teeth. The spinnerets are normally six, and the anal tubercle is above, and well removed from the posterior spinnerets, The Atypidae are a small family of six genera, rather closely related to the Aviculariidae, and by some Arachnologists incor- porated with them. They may be regarded as the representatives of that family in sub-tropical and temperate regions. In form they are strongly built, with smooth integuments, and their legs are short and powerful. Of the twenty-four species hitherto xv CLASSIFICATION 391 described almost all belong to the northern hemisphere. Five are natives of Europe, and two are included in the English fauna. The best known is Atypus ajfinis, which has been found in several localities in the south of England, and which has occurred on the Devil’s Dyke, near Cambridge. The female measures about half an inch in length, the male being smaller. It burrows a deep cylin- drical hole at the edge of a grassy or heathery bank and lines it with a loose tube of silk, which extends considerably beyond the orifice of the burrow, either lying flat on the ground, or raised up and attached to the neighbouring herbage. py4. 993, Arypus affinis, ¢. There is no lid, but the upper end of the tube is always found closed, whether by its elasticity or by the deliberate operation of the spider is not known. The animal is nocturnal in its habits. Another species, A. beckvi, occurs very rarely in the south of England. The genus Atypus has representatives in Central and South Europe, North Africa, Japan, Java, and North America. Of the other genera, Calommata inhabits Central and South-East Asia and Japan, Brachybothriwm, Atypoides, and Hexura are peculiar to North America, while Wecicobothrium comprises a single species (MW. thorelli) native to the Argentine.* Fam. 4. Filistatidae.— Cribellate Spiders of moderate size, usually brown or yellow in colour, with smooth integuments and somewhat long tapering legs. The eight eyes are compactly arranged, and the palpal organs of the male are of simple struc- ture. The six spinnerets are short, the anterior pair being thick and separated. Two pulmonary sacs, with two minute tracheal stigmata close behind them and widely separate. There is but one genus, /i/istata, in this family. About fifteen species have been described, five of which inhabit the Mediterranean region. Three are found in America, and others inhabit Central Asia, the Philippines, and Australia. The genus 1 The three families mentioned above constitute the ‘‘ Araneae Theraphosae ” of Simon, the remaining families being distinguished as ‘‘ Araneae Verae.” The Aviculariidae and the Atypidae are united by some authors to form the Thera- phosidae. 392 ARACHNIDA—ARANEAE CHAP. is not represented in this country, but one species, / testacea, has an extremely wide distribution in the Old World, while 7. capitata extends throughout the American continent. The calamistrum of the female is short, only occupying a portion of the metatarsus of the fourth leg. The cribellum is divided, These spiders weave a web of close texture, of an irregular tubular form. Fam. 5. Oecobiidae (Urocteidae).—Two very remarkable genera constitute this family, Oecobius and Uvoctea. The species of Oecobius, about fifteen in number, are small spiders, inhabiting subtropical countries—and especially desert regions—and spinning a slight web under stones, or in holes in Fra. 204.—A, Occobius maculatus, much enlarged ; B, Uroctea durandi, slightly enlarged. (After Simon.) walls. The female possesses a small transverse cribellum, the two halves of which are widely separated. The calamistrum is but feebly developed. No example has occurred in this country, but nine species have been described in the Mediterranean region. The three species of Uroctea are rather large spiders, two being native to Africa, while the third inhabits China and Japan. They are ecribellate. These two genera very closely resemble each other, not only superficially, but in certain structural details notably the remarkably developed and two-jointed anal tubercle— and their close affinity supples the strongest argument against separating the spiders which possess cribellum and calamistrum into a group by themselves. In both genera the cephalothorax is very broad and rounded at the sides. The eight eyes are compactly arranged. The sternum is broad and _ heart-shaped. XV CLASSIFICATION 39 ios) The legs are nearly of equal length, and the posterior spinnerets have very long terminal joints. Fam. 6. Sicariidae (Scytodidae).— The Sicariidae are a small group of six-eyed spiders, usually with weak legs and slow halting movements; they lve under stones or in outhouses. The cephalothorax is generally smooth and devoid of the median fovea, and the palpal organs of the male are extremely simple. The best known genus is Scytodes, one species of which (S. thoracica) has on rare occasions been found in outhouses in the south of England, in Dorsetshire, and Kent. This is a remarkable spider, about one-third of an inch long, with a pale yellow ground- colour, marked with black spots and patches. The cephalothorax is smooth and dome-shaped, and highest near the posterior end. All the other members of the family are exotic. Lowosceles is found in the Mediterranean region and all over America, as well as in Japan. The median fovea is present in this genus. Sicarius is a native of America and South Africa. It is of stouter build than Scytodes, and the legs are stronger. Drymusa belongs to South Africa. The peculiar New Zealand species Periegops hirsutus is placed by Simon in this family, as is also the North American genus Plectreurys, notwithstanding its possession of eight eyes. Fam. 7. Hypochilidae——Two species only are included in this family, Hypochilus thorelli of North America, and Ectatosticta davidi, a native of China. They have four pulmonary sacs, though they possess little else in common with the “Thera- phosae.” The pedipalpus of the male is very remarkable, the tarsus being almost unmodified, and the very small palpal organ being inserted at its extremity. These spiders are cribellate. Fam. 8. Leptonetidae.—The Leptonetidae are small spiders with smooth and usually dull-coloured integuments. Most of them are cave-living, but some are found amidst vegetable débris in damp spots in forests. The eyes are six in number, and the legs are generally long and thin. There are five genera. Leptoneta has about ten species living in caves in the Pyrenees. ‘The single species of Zelema (7. tenella) has the same habitat. Ochy- rocera has representatives in tropical Asia and America, and is somewhat more ornate than most members of the group. Uso/ila has a single species, inhabiting North America, while 7heotina is found in caves in the Philippines and in Venezuela. Fam. 9. Oonopidae.—The Oonopidae are very small spiders, 394 ARACHNIDA—ARANEAE CHAP. seldom exceeding 2 mm. in length (the largest 4 mm), living among vegetable débris. Oonops pulcher, the only English repre- sentative of the family, is not rare under stones or in the débris at the bottom of hedges. It is a small brick-red spider, easily recognised by its six comparatively large oval eyes, which are pale-coloured, and occupy the whole of the caput. ° The minute spiders of this family were until recently over- looked by collectors in foreign countries, but now more than a hundred species have been described, belonging to some eighteen genera. Thirteen species inhabit the Mediterranean region, occurring especially on the African side. In several genera there is a “scutum” or hard plate on the abdomen. This is the case with Dysderina, which has a wide distribution, as have also Ischnyothyreus and Opopaea, and the non-scutate genus Orchestina. Fam. 10. Hadrotarsidae—This family contains only two species, Hadrotarsus babirusa from New Guinea, and Gmogala scarabeus from Sydney. In general appearance they resemble the scutate Oonopidae, but they have eight eyes, curiously arranged, two large, somewhat triangular eyes being situated near the middle of the cephalothorax, and two groups of three small eyes on either side of the front part of the caput. These spiders are very minute. Fam. 11. Dysderidae.—Six-eyed spiders, with long free labium, and long maxillae provided with a well-developed scopula. The cephalothorax is rather flat, and the abdomen is oval or cylindrical, the integument being smooth and usually rather soft. The palpal organ of the male is of simple structure. The Dysderidae are divided into two sub-familes, DYSDERINAE and SEGESTRINAE, for the most part confined to temperate regions. (1.) The DyspERINAE are easily recognised by a peculiarity of the sternum. Instead of being merely excavated along its border for the reception of the legs, its edge is folded round the coxae to meet the carapace, and thus forms a series of collars or sockets in which the limbs are articulated in perfect isolation from each other. These spiders vary considerably in size, and are gener- ally of a somewhat uniform coloration, never marked with vivid patterns. There are eight genera of this sub-family, two of which are represented in England. Dysdera cambridgii is not a rare spider under stones in rocky xe CLASSIFICATION 395 localities, such as the Isle of Portland, and occurs, though less commonly, all over the country in similar situations, and under the loose bark of trees. It is half an inch in length, with a chestnut-coloured cephalothorax and legs, and dull yellow abdomen. A closely allied species, D. crocota, also occurs more rarely. Harpactes hombergii is common in vegetable débris and under decaying bark. It is about a quarter of an inch in length, of slender form, with black-brown cephalothorax and clay-coloured abdomen. The legs are yellowish and annulated. More than forty exotic species of Dysdera and twenty-four of Harpactes have been described. Another genus of the Dysderinae is Stalita, which comprises three species, inhabiting the caves of Dalmatia and Carniola. (i.) The SEGESTRIINAE include two genera, Segestria and Ariadna. Segestria senoculata occurs in England in similar localities to those where Dysdera cambridgw is found. It is not much smaller than that spider, and has a dark brown cephalothorax and legs and a dull yellow abdomen, with a series of adder-like diamond-shaped black markings along the middle. Two other species have occurred on rare occasions in England, and twelve more are recorded from the various temperate regions of the world. Ariadna is the only Dysderid genus which invades the tropical regions. It includes about twenty species. Fam. 12. Caponiidae.—This is a small family of three genera and about twelve species, remarkable in haying no pulmonary sacs but five tracheal stigmata,’ and in the peculiar arrangement of their six spinnerets, those which are ordinarily median being in the same transverse line with the anterior ones. The single species of Caponia (C. natalensis) inhabits South Africa, while Caponina has two species in South America. These spiders are eight-eyed, but the two median posterior eyes are much the largest, and these alone are present in the remarkable genus ops, of which several species inhabit South America and adjacent islands. Fam. 13. Prodidomidae.—This small family includes about 1 According to Bertkau (in a letter to Simon, cited in Hist. Nat. des Ar. i. p- 327), two pairs of linear stigmata under the anterior part of the abdomen lead, to pulmonary sacs, but to tracheae. 396 ARACHNIDA—ARANEAE CHAP. twenty species of minute spiders from sub-tropical regions. They are eight-eyed, with short smooth legs, terminated by two claws not dentated. The spinnerets are especially characteristic. Prodidomus (Miltia) includes fifteen species from the Medi- terranean region, Africa,and America. Zimris is an Asiatic genus. The single species of Heleis (H. c¥inita) is from the Cape. Fam. 14. Drassidae.— Elongate spiders with low cephalo- thorax. Legs meu rather long, strong, and tapering, terminated by two pectinate claws, armed with spines, oa) scopulate. The body is smooth or short-haired and frequently wnicolor- ous and sombre-coloured, seldom ornate. The eyes, normally eight, are in two transverse rows. The mouth parts (labium and maxillae) are long. Spin- nerets as a rule terminal, and visible from above. This important family includes a large number of species from all parts of the world, fifty-six being natives of the British Isles. There are familar examples in the brown or mouse-coloured spiders which — scurry away when stones are raised, or when _ loose Hie 205.—Drassid Spiders. 1. Drassus lapidosus. bark is pulled off a tree. Wee 3. Zora spinimand 4. The family may be divided into seven sub- families, of which four, DRASSINAE, CLUBIONINAE, LIOCRANINAE, and MICARIINAE, are represented in this country. . G.) The Drasstnaz include more than twenty genera, some of which possess numerous species and have a wide distribution. The following may be mentioned :— xv DRASSIDAE 307 Drassus contains twelve British species. The commonest is D. lapidosus, a large dull brown spider, more than half an inch in length, which lives beneath stones in all parts of the country. At least a hundred species of this genus have been described. Melanophora (= Prosthesima)' includes a large number of species. They are dark-coloured active spiders, many of them jet black and glossy. Seven are recorded from the British Isles, the average size being about a quarter of an inch. They are found under stones. A closely allied genus is Phaeocedus, whose single species (P. braccatus) has occurred, though very rarely, in the south of England. Gnaphosa has fifty-five species, of which twenty-eight are European, and four are British. Gi.) The CLUBIONINAE have the anterior spinnerets closer together, and the eyes more extended across the caput than in the foregoing sub-family. Nearly thirty genera have been established, of which three claim special attention. Clubiona includes more than 100 species, chiefly inhabiting temperate regions. Fifteen are included in the British list. They are mostly unicolorous, and yellow or brown in colour, but a few (C. corticalis, C. compta, etc.) have a distinct pattern on the abdomen. Cheiracanthium is a large and widely spread genus, counting three English species. There are more than a hundred species of the genus Anyphaena, of which one only (A. accentuata) occurs in this country, where it is common upon bushes and trees in the south. Gi.) The LrocrRANINAE include about twenty-four genera, of which Zora, Liocranum, Agroeca, and Micariosoma are sparingly represented in this country. Gv.) The MIcaRIINAE are a remarkable group of Spiders con- taining numerous ant-like mimetic forms. Two species of Micaria alone are English, but that genus is abundantly represented on the Continent, where the species: mount up to forty. They are mostly small, dark, shining spiders, which, though not particularly ant- like in form, recall those insects both by their appearance and movements. Some of the exotic genera, and particularly the South American genus Myrmeciwm, possess remarkable instances of mimetic resemblance to ants. JMcaria pulicaria is a very ' L. Koch replaced Melanophora by Prosthesima, believing the former to be pre- occupied, but according to Simon (Hist. Nat. des Ar. i. p. 341) C. Koch’s use of Melanophora for an Arachnid was antecedent (1833) to Meigen’s employment of it for Diptera, 1838. 398 ARACHNIDA—ARANEAE CHAP, pretty little spider, about a sixth of an inch in length, black, with iridescent hairs, and some white marks on the abdomen. It runs about in a very active ant-like fashion and does not object to the sunshine. It is fairly abundant in England. Fam. 15. Palpimanidae.—This family includes a few genera of exotic spiders. They are especially characterised by the great development of their anterior legs, which are not much used for locomotion, but are frequently raised as the spider moves along, generally somewhat slowly, by means of the other three pairs. The best known genera are Metronax and Stenochilus from India, Huttonia from New Zealand, and Palpimanus from the Mediterranean region, Africa, and South Asia. Fam. 16. Eresidae.—The Eresidae are a small family of cribellate spiders whose systematic position has been the subject of much discussion. In general appearance they resemble the Attidae (vide infra), but this resemblance is quite superficial. On the whole they seem more nearly allied to the following family than to any other. They are stoutly built, with thick, strong legs, and live either in the ground or on bushes, where they weave a close-textured web. One species, Hresus cinna- berinus, has occurred on rare occasions in the south of England, and the male, which is a third of an inch in length, is perhaps the most striking member of our Spider fauna, the abdomen being scarlet, with four (or sometimes six) black spots edged with white hairs. The cephalothorax is black, with red on the postero-lateral borders. The abdomen of the female is black. Fam. 17. Dictynidae.—Cribellate spiders, with oval cephalo- thorax and broad convex caput, with the eyes, normally eight, ranged across it in two straight or slightly curved transverse rows. Basal joints of chelicerae long and strong, often bowed. Leys rather strong. Tarsi three-clawed and devoid of scopula. The Dictynidae are sedentary spiders which weave a web of irregular strands, covered by the close weft which is the product of the cribellum. Some live under stones or in holes in walls, while others spin their webs in bushes or herbage. There are about sixteen genera, of which Dictyna and Amaurobius are the most important. Nearly a hundred species of Dictyna have been described. They are small spiders, usually living in grass and herbage. Thirty species inhabit Europe and the neighbouring coast of reo) XV CLASSIFICATION 399 Africa, and eight of these are natives of Britain. LD. arundinacea is very abundant, especially in heather. It is about an eighth of an inch in length. DD. uneinata is also often met with. Amaurobius, of which about eighty species are known, includes some species of much larger size. Three species are native to this country, A. ferow, A. similis, and A. fenestralis. A. ferox is a large and rather formidable-looking spider, more than half an inch in length, with powerful chelicerae. It is found under stones and bark, and in cellars and outhouses. A. similis is the commonest species in England, though A. fenestralis somewhat replaces it in the north. They are smaller than A. ferox, but are found in similar situations. Fam. 18. Psechridae.—This is a small family of cribellate spiders, consisting only of two genera, Psechrus and Fecenia, and some eight species, all natives of Southern Asia and the adjacent islands. The two species of Psechrus are large spiders. They make large domed webs, which they stretch between trees or rocks, and beneath which they hang in an inverted position. The calamistrum of these spiders is short, about half the length of the fourth metatarsus. Fam. 19. Zodariidae (Enyoidae)—In this family are in- eluded a number of remarkable exotic spiders, most of them somewhat Drassid-like in appearance, but generally with three- clawed tarsi. The group appears to be a somewhat heterogeneous one, the twenty genera of which it consists presenting rather a wide range of characteristics. Cydrela is an African genus of moderate sized spiders, contain- ing five species of very curious habits. They scramble about and burrow in the sand, in which, according to Simon,’ they appear to swim, and their chief burrowing implements are their pedipalpi, which are specially modified, the tarsi in the female bristling with spines, and being armed with one or more terminal claws. Laches(Lachesis) includes some larger pale-coloured spiders found in Egypt and Syria, under stones in very hot and dry localities. Storena has representatives in all the tropical and sub-tropical parts of the world, and numbers about fifty species. They are of moderate size, with integuments smooth and glossy or finely shagreened, usually dark-coloured, with white or yellow spots on the abdomen. Hermippus (Fig. 206) is also African. Zodarion 1 Hist. Nat. des Ar. i. p. 416. 400 ARACHNIDA—ARANEAE CHAP. (Enyo) includes about thirty-five species of rather small, generally unicolorous spiders, very active and fond of the sunshine. They spin no web, but have a retreat under a stone. Their chief prey appear to be ants. Most of the species are native to the Medi- terranean region, the others belong- ing to Central and Southern Asia. Simon includes in this family the remarkable genus Cryptothele, found in Ceylon, Malacca, New Guinea, and various Oceanic islands. They are moderate sized brownish spiders, with hard in- teguments rugged with tubercles and projections. Their most curi- ous characteristic 1s their power of iia. 20d emmep peer eaatne Foam retracting their spinnerets within (After Simon. ) ~ a sort of sheath, so that they become entirely invisible. Fam. 20. Hersiliidae.—This is a very distinct family of spiders, with broad cephalothorax, with well-marked fovea and striae, and small, well defined caput. The eyes, usually eight, are black except the median anterior pair. The legs are long and thin, and the tarsi three- clawed. The abdomen is oval or sub-globular, short haired, and gener- ally of greyish colora- tion. The — spinnerets supply the chief charac- teristic, the posterior pair being long — often ex- cessively long—and two- jointed, the terminal joint tapering and flexible. The colulus is_ large. They are very active spiders, living on tree trunks or walls, or under stones, but spreading no snare. Some of them are of considerable size. Fic. 207.—Hersilia caudata, 2. (After Pickard- Cambridge. ) Xv CLASSIFICATION 401 Hersilia includes nine species native to Africa and Asia. Tama is the only genus represented in the New World, two of its species being found in South America, while others inhabit Africa, Asia, and Austraha. Another genus, Hersiliola, is principally African, but extends into Spain. Fam. 21. Pholcidae.—This is another very well - marked family. The most striking peculiarity of its members is the possession of extremely long and thin legs, the metatarsi being especially elongated, and the tarsi furnished with several false articulations. The eyes are also very characteristic. They are usually eight in number, the two anterior median eyes being black, while the other six are white, and arranged in lateral groups of three, some- times on prominences or stalks. The abdomen is sometimes nearly globular, but more often long and cylindrical. Most of the genera, which, including several new genera lately established by Simon, number more than twenty, are poor in species, but enjoy a very wide distribution. This is explained by the fact that many of them live in cellars and outhouses. This is the case with the genus Pholcus, of which the sole English species Ph. phalangioides is a perfect nuisance in buildings in the most southern parts of the country, “ spinning large sheets of irregular webs in the corners and angles, and adding to them year by year.” Other genera are Artema (Africa, South Asia, Polynesia, America), which includes the largest examples, and Spermophora, a six-eyed genus whose few species are widely distributed. Fam. 22. Theridiidae.—Sedentary spiders, usually with feeble chelicerae and relatively large abdomen. Snare irregular. The Therididae, as here understood, are a very extensive family, and more than half the British spiders (about 270 species) are included within it. This family and the next present unusual difficulties of treatment, and there is great divergence of opinion as to the most satisfactory way of dealing with them. This is chiefly due to the fact that, notwithstanding an infinite variation of facies, important points of structure are wonderfully uniform throughout both the two groups, while any differences that do occur are bridged over by intermediate forms which merge into each other. Simon ~ has become so impressed with the difficulty of drawing 1 Pickard-Cambridge, Spiders of Dorset, p. 77. * Hist. Nat. des Ar. i. p. 594. VOL. IV 2D 402 ARACH NIDA—-ARANEAE CHAP. any Glear line between certain groups which he _ previously classed under the Theridiidae and the spiders commonly known as Hpeiridae, that he has recently removed them from the Theridiidae and united them with the orb-weaving spiders to form the Family Argiopidae, the family name Epeiridae being dis- carded. The groups which, in his view, belong to the Argiopidae will be indicated below. This view has not met with universal acceptance, and notwithstanding the undoubted difficulty of clearly distinguishing between the two families, it is more con- venient in the present work to maintain as a separate family a group of spiders nearly all of whose members possess the easily recognised characteristic of spinning a circular snare. The Theridiidae and the Epeiridae form the great bulk of the sedentary spiders. They do not wander in search of prey, but sit in snares of various structure and wait for their victims to entangle themselves. The spinnerets, organs whose peculiarities are often strongly marked in other families, are here wonderfully constant in their arrangement and general appearance, forming a compact rosette-like group beneath the abdomen. Their eyes, normally eight in number, present an infinite variety of arrange- ment. Their chelicerae and mouth-parts vary considerably, but no abruptness of variation is distinguishable. This is unsatis- factory from a systematic point of view, and the necessary result is that certain groups might with equal propriety be classed with the Theridiidae or the Epeiridae. The latter family will here be taken as including all the orb-weaving spiders and a few groups which appear inseparable from them. We shall consider the Theridiidae as comprising the seven sub-families, ARGYRODINAE, EPISININAE, THERIDIONINAE, PHORON- CIDIINAE, ERIGONINAE, FORMICINAE, and LINYPHIINAE, and shall briefly deal with them in this order. (.) The ARGYRODINAE are very curious spiders with very long and often flexible abdomen. They are commonly parasitic on the circular snares of Epeirid spiders, between the rays of which they spin their own irregular webs. There are three genera, Argyrodes, Ariamnes, and Rhomphaea, which are distributed in the tropical and sub-tropical regions all over the world. (ii.) The Epistninar hardly conform to the character of sedentary spiders, being frequently found outside their webs. In most species the abdomen is narrow in front and broader behind, xv THERIDIIDAE 403 where it is abruptly truncated or bluntly pointed. The genus Episinus is widely distributed, and one species, #. truncatus, is one of our most peculiar English spiders. It occurs occasionally under ledges of grassy or heathery banks. The genus Zomoxena is an inhabitant of tropical Asia. Janulus is found in the same regions, and in tropical America. (ii.) The THERIDIONINAE are a large group of spiders, often very ornate, and spinning snares of irregular threads running in all directions. The abdomen is usually more or less globular. The chelicerae are small and weak, and the paturon is transversely (not obliquely) truncated for the reception of the small unguis or fang. The somewhat long thin legs are almost or entirely destitute of spines. We may consider certain genera as typical of the various groups into which this sub-family naturally falls. Zheridion 1s the richest genus of the entire order, numbering some 520 species, of which seventeen inhabit the British Isles. During the summer months nearly every bush is studded with the irregular webs of these little spiders, generally prettily coloured, and with globular abdomen. The commonest is 7° sisyphium, which swarms on holhes and other bushes all over the country. One of the handsomest is 7. formosum, a rather local species, about a sixth of an inch in length, with the abdomen beauti- fully marked with oblique lines of white, yellow, red, and black. T. tepidariorum, common in conservatories, is like a large and plainer edition of 7. formosum. T. riparium is remarkable for the curious earth-encrusted tube which it forms for the recep- tion of its egg-cocoon. 7. bimaculatum may often be seen among coarse herbage, holding on to its ridiculously large egg- cocoon ; it is a small spider, and the sexes are more than usually unlike. Latrodectus and Dipoena are associated exotic genera, includ- ing some of the largest species of the group. Latrodectus is peculiarly interesting on account of the great reputation for especially poisonous properties which some of its species have acquired. The New Zealand “Katipo” is JL. scelio, while L. 13-guttatus enjoys an almost equally evil reputation as the “malmignatte” in Corsica. The American species L. mactans (Fig, 197, p. 362) is also considered highly venomous. These spiders form their irregular webs on low bushes, and it is curious 404 ARACHNIDA—ARANEAE CHAP. that they are usually marked with red or yellow spots on the abdomen. They have been referred to in the section on the venom of spiders (see p. 362). The genus Steatoda possesses one English species (S. bipunctata) which is extremely common in buildings and in the angles of walls, and is a rather striking spider, with dark cephalothorax, and livid brown abdomen with a broken white stripe down the middle. Several closely allied genera are also sparingly repre- sented in this country, among which may be mentioned Crustu- lina (two species), Asagena (one species), Zeuvtana (two species), Lithyphantes (one species), Laseola (five species), and Huryopis (two species). In some of these the male is provided with a stridulating organ between the thorax and abdomen (Fig. 183, p- 327). The remarkable genus TZetrablemma (see p. 318) is considered by Simon to have affinities with this group, though Pickard-Cambridge, who first described it, is inclined to rank it among the Dysderidae. (iv.) The PHORONCIDIINAE are a remarkable group of spiny Theridiids whose superficial resemblance to the Gasteracanthinae of the Epeiridae (see p. 409) has often deceived Arachnologists as to their true affinities. There are eight genera, all exotic, inhabiting hot countries, and spinning a Theridion-like web on bushes. Phoroncidia has twelve species in South Asia and Madagascar. Trithena (Fig. 208) is its American representative, five species being found in South America, Ulesanis has Fic. 208.—Trithena about twenty species, and extends from South tricuspidata 2. America to Australia. x 38. (After f Simon.) (v.) The ERIGONINAE are an Immense group of minute, sober-coloured spiders, which include the “ Money-spinners ” of popular nomenclature, and are largely responsible for the gossamer which fills the air and covers every tuft of grass in the autumn. The number of species described is very large and constantly increasing, and more than a hundred are recognised as British. Desperate efforts have been made of late years to grapple with this almost unmanageable group, but the multitude of genera which have been proposed can hardly as yet be considered to be finally established. The small size of these spiders, which XV THERIDIIDAE 405 renders the aid of a microscope necessary to make out their structural peculiarities, robs them of their attractiveness to any but the ardent Arachnologist, but they number among them some of our most remarkable English forms, and many of them well repay examination. The smallest English species, Panamomops diceros, measures about 1 mm. (about 5); inch) in length. Many of the groups are jet black, some with dull and others with shiny integuments. They are never greatly variegated in hue, but the glossy black of the cephalothorax, combined with red-brown or yellow legs, gives to some species a rather rich coloration. It is impossible here to deal with this sub-family in detail. Some of its members must be familiar enough to everybody, and the reader is recommended to spend an hour of a warm autumn day in watching them depart on the ballooning excursions, of which a description has been given (see p. 341), from the knobs which surmount iron railings in a sunny spot. Among them he is pretty sure to find the genus #7rigone—containing some of the largest members of the group— strongly represented. In some species the male presents a remarkable difference from the female in the structure of its cephalothorax, which has the head region produced into eminences sometimes of the oddest con- formation. An extreme example is seen Fic. 209.—Profile of cephalo- . in Walckenaera acuminata, a fine species in which the male caput is produced into a sort of spire, bearing the eyes, and nearly as high as the cephalothorax is long (Fig. 209, 3). (vi.) The ForMIcINAE include only thorax of 1, Lophocarenum insanum ; 2, Dactylo- pisthes digiticeps; 3, Walckenaera acuminata (+ abdomen); 4, Diplo- cephalus bicephalus ; 5, Metopobractus rayt. two genera, Mormicina (South Europe) and Solenysa (Japan). They are somewhat ant-like in appearance. (vil.) The Lryypuiinak are closely allied to the Erigoninae, but the legs are usually armed with spines, and very commonly the female has a dentated claw at the end of the pedipalp. We include here about thirty genera of spiders of moderate or small size, living for the most part on bushes or herbage. The 406 ARACHNIDA—-ARANEAE CHAP. characteristic Linyphian web is a horizontal sheet of irregular strands, anchored to neighbouring twigs or leaves by cross threads in all directions, and the spider generally lurks beneath the web in an inverted position. Some of the larger species are very familar objects, Linyphia triangularis being one of the most abundant English spiders, filling furze and other bushes with its extensive spinning work. The sub-family may be roughly divided into three groups, of which the first is small, consisting of only three exotic genera of one species each. Donachochara may be taken as the type genus. They are moderate-sized spiders with rather short legs, found in France and Holland. The second group consists of a number of genera of small spiders, sober-coloured, and generally more or less unicolorous in brown, yellow, or black, living in herbage. The sexes are much alike, the males never exhibiting the excrescences on the caput so often met with in the Erigoninae. The genus Z%neticus may be considered the type. It includes about forty species, of which about half are British. They are mostly dull yellow or brown spiders, averaging perhaps the eighth of an inch in length. Allied genera which are represented in England are Porhomma (twelve species), JZicroneta (twelve species), Sintula (twelve species). The American cave-genus Anthrobia comes here. The third and last group is that including Linyphia and allied genera. They are moderate-sized or small spiders with long spiny legs and particularly long tarsi. The abdomen is generally decorated. The caput is frequently rather prominent and crowned with hairs. Of the large number of spiders which have been described under the generic name of Linyphia, Simon? only admits about fifty species. Ten are included in the British lst. JZ. triangu- laris has already been mentioned, but there are other common species, as L. montana, L. marginata, and L. clathrata. The members of most of the associated genera are rather small in size. We may briefly mention Bolyphantes, Bathyphantes, Lephthy- phantes, and Labulla, all of which include English species.? Fam. 23. Epeiridae.—This family includes all the spiders 1 Hist. Nat. des Ar. i. p. 692. ’ The Erigoninae, Formicinae, and Linyphiinae, together with the Epeiridae, form Simon’s family of Argiopidae. XV EPEIRIDAE 407 which spin circular or wheel-like snares, the highest form of spider industry, together with a few forms so closely allied in structure to orb-weaving species as to be systematically insepar- able from them. It is practically co-extensive with the Argio- pinae, Tetragnathinae, and Nephilinae of Simon’s Argiopidae in the Histoire naturelle des araignées.' No one is unfamiliar with the orbicular snares, the structure of which has already been described with some minuteness (see p- 344), and some of the spiders which construct them are among the best known members of the order. It is impossible here to deal with the multitudinous forms embraced by this family. We must mention those genera richest in species, and some others of special interest. It will be con- venient to indicate eight sub-families or groups, which include most of the forms likely to be met with. These are the THE- RIDIOSOMATINAE, 'TETRAGNATHINAE, ARGIOPINAE, NEPHILINAE, EPEIRINAE, GASTERACANTHINAE, POLTYINAE, and ARCYINAE. Gi.) The THERIDIOSOMATINAE are a small group which might with equal propriety be classed with the Theridiidae or the Epeiridae. TZheridiosoma argenteolum is a rare spider in Dorset- shire. It is a minute spider, one-twelfth of an inch in length, with silvery white globular abdomen variegated with reddish brown, and yellow cephalothorax with darker caput. Some allied spiders spin a roughly circular snare. Gi.) The TETRAGNATHINAE consist chiefly of two genera, Pachy- gnatha and Tetragnatha. The first consists of spiders which are not orb-weavers, but live in herbage, especially in swampy places. Two species, Pachygnatha clerckii and P. degeerti, are common in England, and a third, P. listeri, is sometimes met with. They are rather striking, prettily marked spiders, with strongly developed chelicerae. The species of 7etragnatha are true orb-weavers, and may easily be recognised by their cylindrical bodies, elongated chelicerae, and long legs, stretched fore and aft along the rays of their webs. Five species have been recorded from England, and the genus contains at least a hundred species in all; almost every country in the world, regardless of its latitude, supplying examples. 1 7,e. as developed in the course of the work, not as set forth on p. 594 of vol. i., where five sub-families are established (Theridiosomatinae, Arciinae, Eurycor- minae, Amazulinae, Poltyinae), which are afterwards merged in the Argiopinae. 408 ARACHNIDA—ARANEAE CHAP. Simon associates with these spiders the genus Meta, which includes perhaps our commonest Epeirid, JMeta segmentata, a smallish and not very striking Orb-weaver, with a rather elon- gated or sub-cylindrical abdomen. Every garden is pretty sure to abound in it. (iii.) The ARGIOPINAE include many large and very striking members of the Epeiridae. There are about a hundred species of Argiope (Fig. 198, p. 379) spread over the tropical and sub- tropical countries of the world. They rarely invade the temperate regions, but A. bruennicht is found in South Europe, and J. trifasciata in Canada. The large spiders with transverse bars of yellow or orange on their abdomen, and often with a silvery sheen, belong to this genus. The species of the allied genus Gea are generally much smaller, and their abdomen more elongated. Both genera are found in tropical and sub-tropical regions all over the world. Argiope always sits in the middle of its circular web. There are invariably some flossy zigzag bands of silk stretched between two of the rays, and the web is generally accompanied by an irregular net on its border, where the much smaller male may be found. (iv.) Among the NEPHILINAE are to be found the largest Epeirids. Indeed, the largest yield in size only to the Avicu- lariidae. Nephila is a tropical genus, numbering about sixty species. The abdomen is generally elongated and somewhat cylindrical, and is strikingly variegated. It is in this group that the disparity in size between the sexes is most marked (see p. 379). (v.) The Eprrrinak! include the bulk of the Orb-weavers, and form a very extensive group. Five genera and twenty-eight species are in the British list. 1 Simon’s treatment of this group in his Hist. Nat. Ar. does not appear to us satisfactory. He revives the name Araneus as a generic term, a proceeding to which there are very valid objections, and merges in it, in whole or in part, about twenty-five generally received genera, including 800 species. He then proceeds to break up the genus Araneus into six entirely artificial ‘‘series,” according to the eyes. However unsatisfactory the merged genera may be, nothing seems to be gained by this proceeding. The facts about ‘‘Araneus” are these. Clerck and Linnaeus used the name ‘‘4raneus” for every member of the order. Latreille, in sub- dividing the order, retained the name for 4. (Hpetra) diademata (1804), but later (1827) transferred it to 4. (Tegenaria) domestica. Walckenaer, seeing the impro- priety of using Araneus as a generic term, discarded it, establishing Epeira, which has since obtained universal recognition. XV EPEIRIDAE 409 No spider is more familiar than Hpeira diademata (Fig. 181, p. 325), the Garden-spider, par excellence, which attains its greatest size and spreads its largest snares in the autumn. The smaller and much less conspicuous Zilla w-notata is sure to be found abundantly in the same locality. Several other Epeirids are to be found in this country, especially in the south, by sweeping heather or bushes with a net, or shaking the boughs of trees over an umbrella or other receptacle. The little apple-green species is Epeira cucurbitina. E. cornuta is extremely common in marshy places all over the country. In furze bushes, and often among sedge in swampy places, will frequently be found #. quadrata, one of the largest and handsomest species we possess. The ground-colour may vary from orange-red to green, and there are four conspicuous white spots on the abdomen. The tent- like retreat which this spider makes near its snare often catches the eye. E. umbratica is a dark flat, somewhat toad-hke Epeirid of retirmg habits, which stretches its snare usually on wooden palings, between the timbers of which it squeezes its flat body, and waits for insects to entangle themselves. Two of our finest Epeiras, 2. pyrami- data and £. angulata (Fig. 210), are seldom met with, and only in the south. Our only Cyclosa (C. conica) is easily recognised by the peculiar form of its abdomen, which is greatly prolonged beyond the spinnerets. It is a small, rather dark species, which constructs a particularly perfect snare. Five British Epeirids belong to the genus Singa. They are small creatures, not exceeding a sixth of an inch in length. They live in heathery and marshy localities. (vi.) The GASTERACANTHINAE are a remarkable group of Epeirids, characterised by the hard and coriaceous integument covering the abdomen, which is usually furnished with a number of more or less formidable thorn-like spines, calculated to render these spiders by no means pleasant eating for insectivorous birds. An even more constant characteristic is the presence on the back Fic. 210.—Epeira angulata, @ . 410 ARACHNIDA—ARANEAE CHAP. of the abdomen of a number of “ sigilla,” or somewhat seal-like impressions arranged symmetrically, four forming a trapezium in the middle, while the others are dis- tributed round the border. There are about 200 species of Gastera- cantha, all natives of tropical countries. The spiders of the genus Micrathena (Acrosoma) have a more elongate cephalo- thorax, and sometimes the spines are ex- ceedingly long, far exceeding the length of the body proper. Among the less spiny members of this group are some remarkable mimetic ant-like forms. (vii.) The PotryryaE include some ae par te remarkable spiders, found in Africa and be South Asia for the most part, though sparingly represented in America and Oceania. They are generally largish spiders, often with a very odd conformation of the abdomen, which is generally much raised. The type genus is Poltys. (vili.) The ArcyINAE, which are more characteristic of Australia and the neighbouring islands, are a small group of spiders, usually yellow with black markings, and with the somewhat square-shaped cephalothorax usually prominent at the angles. The type genus is Arcys. Fam. 24. Uloboridae.—The Uloboridae are cribellate spiders, with rather elongate cephalothorax, devoid of median fovea. The eribellum is transverse and generally undivided. The first pair of legs’ are usually much the longest. The metatarsi of the fourth legs, in addition to the calamistrum, bear a number of generally regularly arranged spines. The eyes are often situated on tubercles. Three sub- families are recognised, DINOPINAE, ULOBORINAE, and MIAGRAMMOPINAE. (i.) The DrnopInak are a small group comprising only two genera, Dinopis and Menneus. The calamistrum is short, occupy- ing not more than half of the metatarsus. Twenty species of Dinopis and six of Menneus are scattered over the tropical regions of the world. (ii.) The ULoporrnak include a number of spiders which have been described under several generic names, but are now considered to fall into two genera, Sybota and Uloborus. Sybota has only two XV CLASSIFICATION Aviat species, one in the Mediterranean region and one in Chili. There are about sixty species of Uloborus, some of which have a wide distribution, while many (e.g. U. republicanus, of Venezuela) are social. The type species, U. walchenaerius, is a very rare spider in England. (ii.) The MIAGRAMMOPINAE include two genera containing some very interesting forms. The genus Miagrammopes, of which twenty species have been deseribed, though the number is probably far greater, is characterised by a very long cylindrical abdomen, and by the apparent possession of only four eyes, in a transverse row. These are really the posterior eyes; and the anterior eyes, or some of them, are present in a very reduced condition. Little is known of the habits of these spiders. The other genus, Hyptiotes, though only boasting three species, possesses a special interest on account of the remarkable snare constructed by the spiders which belong to it. This has already been described in the section upon defective orb-webs (see p. 349). The type species, 7. paradoxus, is very rare in England, and though small and inconspicuous, it is certainly one of the most curious members of our Spider fauna, Fam. 25. Archeidae.—This small family includes certain remarkable fossil spiders from Baltic amber, and two rare recent forms, Archea (Hriauchenus) workmani from Madagascar, and sae tere a Mecysmauchenius segmentatus from America. cy The chelicerae, which are extraordinarily long, are articulated far away from the mouth-parts. The caput is clearly marked off from the thorax, and is much raised. In several other respects these spiders are very distinct from all other members of the order. Fam. 26. Mimetidae.—The Mimetidae form a small group in general appearance recalling the Therididae, with which family they were for a long time incorporated. The chief genera are Ero, Mimetus, and. Gelanor. Ero furcata (=thoracica) is a pretty little spider, not rare among grass in England. The upper side of its very convex abdomen is marked with red, yellow, and black, and bears two little protuberances or humps near the middle. It is only about an eighth of an inch long. 412 ARACHNIDA—-ARANEAE CHAP. Its interesting egg-cocoon has already been alluded to (see p. 358). E. tuberculata has been found on rare occasions in this country. There are about ten other species of ro, all small spiders, and living in temperate regions. The genus J/imetus Gn which is merged Blackwall’s Ctenophora) includes a number of larger, more strongly-built spiders, living for the most part in tropical countries. The genus Gelanor (Galena) is the American representative of the group, its three species being rather large spiders, inhabiting Central and South America. The males of this genus have remarkably long and slender pedipalpi, much longer than the whole body. Fam. 27. Thomisidae—The Thomisidae are the Latigrade spiders of Latreille, and the “ Crab-spiders” of popular nomen- clature. Their legs are extended more or less laterally instead of in the normal fore and aft directions, and their progression is frequently strikingly crab-like. They form a very large group of more than 140 genera, including spiders of every size, and they are to be found in every quarter of the world. Forty-three species are British. Many strange forms are included in this group, and several of the sub-families into which it has been divided contain only one or two genera. The bulk of its members fall into the sub-families THOMISINAE, PHILODROMINAE, and SPARASSINAE. G.) The THoMISINAE (MISUMENINAE of Simon’s Hist. Nat.) include what may be called the more normal members of the family, distributed among more than sixty genera. Six of these genera are represented in the British Isles. Our commonest Crab-spider is probably Yysticus cristatus, abundant everywhere in grass and herbage. Young specimens may often be seen upon iron railings in the autumn. Twelve other species of that genus are on the British list. They are of small or moderate size, rarely exceeding a quarter of an inch inlength. A closely allied genus is Oxyptila, of which we have seven species. The more striking members of this sub-family to be found in England are our single representa- tives of the genera Miswmena, Diaea, and Thomisus. Misumena vatia is a handsome species, the female measuring sometimes more than a third of an inch, and having its large yellow or green abdomen marked, in many specimens, with a pair of bright red bands, which, however, are not always present. The males ee THOMISIDAE 413 are much smaller and darker. It is common in some parts of England, especially in the south, where it is to be sought for in bushes and trees. Diaea dorsata is one of our prettiest British species, with light ereen legs and cephalothorax, and a yellow abdomen with a red-brown central marking. It is common in the New Forest and other southern localities. The female attains a quarter of an inch in length. Thomisus onustus, a rare spider among heather, is recog- nisable by the shape of its abdomen, which is_ broadest behind and abruptly truncated. When adult the abdomen is a pale yellow, but the young are suffused with a pink hue closely corresponding with that of the heather blossom in which they are frequently found sitting. Gi.) The PHILODROMINAE have the cephalothorax more rounded in front, and the legs, especially the second pair, Fie, 213.—Thomisid spiders. A, Micrommata usually longer than in the virescens, 9; B, Xysticus pini, 2; C, MOsiniae. Mliereseare ten Philodromus margaritatus, §; D, Tibellus oblongus, 2 . genera, of which the most important is Philodromus, which numbers about a hundred species. They are active spiders, living upon bushes and trees, and most of them are inhabitants of temperate regions. We have about twelve species in the British Isles. The commonest is Ph. aureolus, which is abundant on bushes in most parts of the country. Some species are very prettily marked, and one, Ph. margaritatus (Fig. 213, C) presents a very good example of protective colora- tion, being almost indistinguishable on the blue-grey lichen on tree trunks, where it lies in wait for insects. Another important genus, including some fifty species, is 414 ARACHNIDA—ARANEAE CHAP. Thanatus, extending from tropical to arctic regions, but very sparingly represented in England. 7h. striatus ( = hirsutus) occurs occasionally, and one example of the fine species 7h. formicinus has been taken in the New Forest. The members of this genus as a rule affect dry and sandy habitats. The genus Z%bellus includes few species, but has a wide dis- tribution. The type species 7” oblongus (Fig. 213, D) is found in the temperate regions all over the world, and is common in Eng- land. It is a pale straw-coloured spider with a much elongated abdomen. It closely resembles the stems of dry grass in hue, and when alarmed it remains perfectly still with its legs embracing the stem and its abdomen closely applied to it. (iii.) The SPARASSINAE! include most of the large Latigrade forms, and number about forty genera. Heteropoda venatoria is a cosmopolitan species, and though proper to warm countries, is often introduced here on hothouse plants, and has been known to establish itself in the open air in botanical gardens. Our only indigenous member of this sub- family is Micrommata virescens (Fig. 213, A). This striking spider is found, though rarely, in the south of England. The female is half an inch in length and of a vivid green hue, while the more cylindrical abdomen of the male is yellow with three longitudinal scarlet lines. Other genera are Sparassus, Torania, and Delena. (iv.) The APHANTOCHILINAE include two curious genera which are exclusively American. The labium is much reduced and the sternum is shortened, terminating between the third pair of legs. The species of Aphantochilus are largish, glossy-black spiders, sometimes spotted with white. Some of them mimic ants of the genus Cryptocerus. The other genus is Bucraniwm. (v.) The STEPHANOPSINAE include about sixteen genera, of which the best known are Stephanopsis and Regillus. There are about fifty species of Stephanopsis, most of them Australian, while the eight species of Regillus belong to Africa and South Asia. The mimetic form Phrynarachne decipiens has already been alluded to (see p. 574). (vi.) The SELENOPINAE consist of a single genus, Selenops, of 1 Simon, in his Histoire naturelle des araignées, removes the Sparassinae and the Selenopinae to the Clubionidae, considering that, notwithstanding the direc- tion of their legs, they have a greater affinity with that group than with the other Thomisidae. XV CLASSIFICATION 415 which ten or twelve species are known, some of which are very widely distributed, though confined to hot regions. These spiders, which are all large, are easily recognised by their extremely flat bodies and the peculiar arrangement of their eyes, all eight of them being placed more or less in a single transverse line. Fam. 28. Zoropsidae—The Zoropsidae are cribellate spiders of large size, with well-developed scopulae on tarsi and metatarsi. The eribellum is divided, and the calamistrum, which is very short, is not well developed. Most are inhabitants of hot regions, where they live under stones or bark. Zoropsis has six species, chiefly inhabitants of North Africa, though representatives occur on the European side of the Mediterranean. Acanthoctenus has - two species in South and Central America. Fam. 29. Platoridae—The Platoridae are Thomisid-like, medium-sized spiders, generally with a uniform yellow or brown coloration. The spinnerets are their most characteristic features. The median pair present a large flat surface studded with two parallel rows of large fusulae, while the anterior pair are situated outside them, and are thus widely separated. There are only three genera, and very few species of this family. Plator insolens is a Chinese species. Doliomalus and Vectius belong to South America. Fam. 30. Agelenidae—Sedentary spiders with slight sexual dimorphism ; with three tarsal claws and devoid of scopulae. The Agelenidae spin a more or less extensive web of fine texture, usually accompanied by a tubular retreat. Our com- monest cellar spiders belong to this group, which may be divided into three sub-families, CYBAEINAE, AGELENINAE, and HAHNIINAE. (i.) The CYBAEINAE include some sixteen genera, of which two deserve special mention on account of the peculiar habits of the spiders belonging to them. Desis is a genus of marine spiders, said to live on coral reefs below high-water mark, and to remain in holes in the rock during high tide, enclosed in cocoons impermeable to the sea-water. At low tide it is stated that they come forth and prey upon small crustaceans. Argyroneta has only one species, A. aquatica, spread throughout Europe and North and Central Asia. It is the well- known “ Water-spider,” which is so often an object of interest in aquaria. 416 ARACHNIDA—ARANEAE CHAP, (ii.) The AGELENINAE also contain sixteen genera, but it is a much larger group, some of the genera being rich in species. They are mostly moderate or large-sized hairy spiders, living in temperate or cold climates. There are about fifty species of Tegenaria, seven of which have been recorded as British. Our commonest Cellar-spider is 7. derhamii, but the very large long-legged species found in houses in the southern counties of England is 7. parietina (= guyonit = domestica). There are not many species of Agelena, but one, A. /abyrinthica, is a common object in this country, with its large, close-textured web and accompanying tube spread on grassy banks by the wayside. Coelotes atropos is a formidable-looking spider, found occasionally under stones in England and Wales. Another genus, Cryphoeca, has three British representatives. (iii.) The HAHNIINAE are recognised at once by their spinnerets, which are arranged in a single transverse line, the posterior pair being on the outside, and generally much the longest. Hahnia contains several species of very small spiders, of which four or five are British, usually occurring among moss or herbage. The aberrant form Nicodamus (Centropelma), usually placed among the Theridiidae, is removed by Simon to the Agelenidae, forming by itself the sub-family Gv.) NIcoDAMINAE. Fam. 31. Pisauridae.——The Pisauridae are hairy, long-legged spiders, intermediate, both in structure and in habits, between the Agelenidae and the Lycosidae. Many new genera have recently been added to the group, but many of them only include one or two species. Pisaura is spread throughout the temperate regions of the Old World, and P. (Ocyale) mirabilis is common in England, being found abundantly in woods and on commons. It is a striking spider, more than half an inch in length, and its elongate abdomen is marked on either side with a sinuous longitudinal white band. There are some thirty species of Dolomedes scattered over the temperate regions of the world. D. jimbriatus is a rare species in marshy spots in the south of England, and is one of the largest British spiders. The ground-colour is deep brown, with two longitudinal yellowish stripes both on cephalothorax and abdomen. The genus Dolomedes is replaced by Thawmasia in South America. XV LYCOSIDAE AW, Fam. 32. Lycosidae.—These are what are popularly known s “ Wolf-spiders.” They are vagabond hunting spiders, spinning no snare, but chasing their prey along the ground, and in the breeding season carrying their egg-bags with them, attached be- neath the abdomen. Some of aon burrow in the loose earth or sand, but others seem to have nothing in the way of a habitation. The arrangement of the eyes is very characteristic. They are in three rows. The front row consists of four small eyes above the insertion of the chelicerae, and directed forwards. Two com- paratively very large eyes form the next row, and occupy the upper angles of the facies, being also directed forwards. The third row consists of two medium-sized eyes placed dorso-laterally on the caput, some distance behind the rest, and looking upwards. The tarsi are three-clawed. The so-called “Tarantula” spiders belong to this group, though the name has been so abused in popular usage, and has passed through so many vicissitudes in scientific nomencla- ture, that it is diffi- cult to tell what creature is intended by it. In America the Aviculariidae are commonly called Tarantulas. The two chief genera of this exten- sive family are Lycosa and Pardosa. The genus Lycosa includes about 400 species. It has béen —— wa 0 ume Fia. 214.—Lycosid Spiders. 1, Lycosa fabrilis, ? ; to time into various 2, Lycosa picta, 2 ; 3, Pardosa amentata, @. genera (Zvrochosa, Pirata, Tarentula, stank but these glide into each other by im- perceptible degrees, and are now discarded. ‘They are large or moderate-sized spiders, found in every part of the world. About twenty species are British, some of them being fine and hand- VOL. IV 2E 418 ARACHNIDA—ARANEAE CHAP. somely marked. One of the prettiest is Lycosa picta, common on the sandhills in some localities. Some exotic species are very large, Lycosa ingens, from Madeira, measuring sometimes more than an inch and a half in length. Pardosa (Fig. 188, p. 341) is not so rich in species, but the individuals of some species are wonderfully numerous. Hundreds of P. lugubris, for example, may be seen scampering over the dead leaves of a wood in the autumn. These spiders are generally sombrely coloured and well covered with hair. Perhaps the com- monest and most° widely-spread species in this country is P. amentata. Fam. 33. Ctenidae—The Ctenidae are Zycosa-like spiders, having in certain points of structure close affinities with the Pisauridae and the Sparassinae of the Thomisidae. The limits of the family are not well defined, and many arachnologists place in it some of the genera allotted above to the Pisauridae, while others do not consider the group sufficiently marked off to con- stitute a separate family at all. As here understood they are equivalent to the Cteninae of the Clubionidae in Simon’s /Zistovre naturelle. The eyes are arranged in the Lyeosa fashion, but the tarsi have only two terminal claws and well-developed “ claw- tufts,” frequently accompanied by a scopula. There are strong, regularly-arranged spines under the tibiae and tarsi. There are about fifteen genera. Uliodon numbers six species of large hairy spiders in Austraha. Ctenus is rich in species, having about sixty, found in all hot countries, but especially in America and Africa. They are also of large size and usually of yellowish coloration, often diversified by a pattern on the abdomen. The fifteen species of Leptoctenus are proper to tropical Asia. Acantheis from South Asia and Hnoplectenus from Brazil are more slender, elongate forms, recalling Zetragnatha. Caloctenus includes a number of Pardosa-like spiders found at a high elevation in South America. The Ctenidae have the habits of the Lycosidae, and are wandering spiders, some forming a burrow in the ground. Fam. 34. Senoculidae.—The South American genus Sen- oculus (Labdacus) alone constitutes this family. The species are probably numerous, but ten only have been described. They are moderate-sized spiders, spinning no web, but running with astonishing speed over the leaves and stems of plants. The XV CLASSIFICATION 419 generic name is really inapplicable, as there are eight eyes, but the anterior laterals are much reduced. The abdomen is long, and the legs are long and unequal, the first pair much the longest and the third much the shortest. Fam. 35. Oxyopidae.—The Oxyopidae form a well-marked group, with oval cephalothorax somewhat narrowed in front, and lanceolate abdomen. The eight black eyes have a characteristic arrangement, and the anterior medians are always very small. The legs are long and tapering, and not very unequal, and are furnished with particularly long spines, which give these spiders a very characteristic appearance. There are eight genera, of which the most important are Pucetia and Oxyopes. Pucetia contains a number of rather large spiders, generally bright green, often variegated with red. They affect particular plants. For instance, P. viridis, which occurs in Spain, is always found on Ononis hispanica. There are about thirty species of this genus distributed over the tropical and sub-tropical regions of the world. Oxyopes numbers many species, certainly more than fifty, and has a similar distribution, but some of its members invade colder regions. They are of rather small size. 0. lineatus is a very rare spider in the south of England. The Oxyopidae are diurnal spiders, running over plants in search of prey, and often leaping, after the fashion of members of the following family. Fam. 36. Attidae (Salticidae).— Wandering spiders with cephalothorax broad anteriorly, and bearing eight homogeneous eyes in three rows. Four eyes, largely developed, are directed forward ; the remaining four eyes are placed dorsally in two rows, the first pair beng much reduced in size. The Attidae or Jumping-spiders form the most extensive family of the whole order, the known species amounting to something like four thousand. It is only of late years that their vast numbers have begun to be realised, for their vagabond habits and great activity enabled them to a great extent to elude the earlier collectors, whose methods were not as thorough as those now in vogue. Their real home is in the tropical regions, temperate fauna being comparatively poor in Attid species. France boasts nearly 150, but only 37 are recorded for the British Isles, and 2 at least of these are recent introductions. Some of the tropical forms are most brilliantly coloured, 420 ARACH NIDA—ARANEAE CHAP. glowing with vivid colours and metallic hues, and they have fre- quently excited the admiration of travellers. The coloration is nearly always due to the hairs and scales with which the spiders are clothed, and is, unfortunately, almost incapable of preservation in the collector’s cabinet. These spiders are all wanderers, spinning no snares, though they form a sort of silken cell or retreat, in which the female lays her eggs. Their habits are diurnal, and they delight in sunshine, They stalk their prey and leap upon it with wonder- ful accuracy. They invariably attach a thread at intervals in their course, and on the rare occasions when they miss their aim while hunting on a perpendicular surface, they are saved from a fall by the silken line proceeding from the spot whence the leap was made. The movements of these spiders are sufficient to indicate their systematic position without entering upon structural details, but - their eyes deserve a special mention. They are all dark - coloured and very unequal in size, and they occupy the whole area of the caput, usually forming a large quadrilateral figure. Four large eyes occupy the facies or “ forehead,” the medians being especially large. Next come two very small eyes, behind the anterior laterals, and lastly two of medium size at the posterior corners of the caput. This vast family does not lend itself easily to Fic. 215 -—Attid Spiders. A, Salticus scenicus, 6 ; division into sub-families, mica, 9; D, Ballus variate, and it. will be impos- sible here to do more than indicate a very few of the multitudinous forms. The most familiar British example is Salticus scenicus (Epi- blemum scenicum), the little black and white striped spider to be XV ATTIDAE 421 seen hunting on walls and fences during the summer, arpissa muscosa 1s the largest English species, measuring about half an inch. It has a brownish-yellow coloration, and is found, though not commonly, in similar situations. Attus pubescens affects grey stone walls, on which it is nearly invisible except when moving. The other British species are mostly to be found on trees and shrubs or among herbage, or hunting over bare sandy spots in the sunshine. XVII HARVEST-SPIDERS 441 Members of this group vary considerably in habit. The best known forms are exceedingly active, and trust to their speed in endeavouring to escape from danger, at the same time emitting an odorous fluid from two apertures situated just above the coxae of the first pair of legs. These active Harvestmen are only found in the mature state at certain seasons of the year, and are believed, therefore, to live only for a single season. Slow-moving forms, likethe Nemasto- matidae and the Trogu- lidae, which live amidst grass and herbage, have a much longer duration of life. In danger they remain perfectly still, and trust to their earthy appearance to escape observation. They are stated to be extremely thirsty ; animals, and have been observed drinking from the dewdrops on her- bage. It is probably on this account that they are sometimes seen attacking juicy vege- table matter, for with- out doubt they are essentially carnivorous. The larvae of insects, young spiders, mites, and myriapods are their customary food. It is not requisite that the prey should be alive, but they will not touch anything mouldy. Notwithstanding their apparently weak mouth-parts, they do not merely suck the juices of their victims, but masticate and swallow solid particles. Cannibalism is frequently observed among them. The males fight fiercely with one another at the breeding DE ac \ Fic. 229,.—Oligolophus spinosus. (After Pickard-Cambridge. ) 442 ARACHNIDA—PHALANGIDEA CHAP, time. The females, with their long extrusible ovipositors, place groups of twenty to forty eggs in small holes in the ground or under stones or bark, unprotected by any form of cocoon. The eggs hatch into fully-formed Phalangids, which are at first white, but attain their coloration after the first moult. They subse- quently moult from five to nine times. The distribution of this group is world-wide, and some of the exotic species are very remarkable in form. Only twenty-four species have as yet been recorded in this country. External Structure——In the Phalangidea there is no con- striction between the cephalothorax and the abdomen, and in the Ischyropsalidae alone is the distinction between them readily observable. This is due to the partial or complete fusion of the first five segments of the abdomen with the carapace or cephalo- thoracic shield in most species, these segments being indicated, if at all, merely by faint striae or successive transverse rows of spines or tubercles. In the forms possessing hard integuments (Gonyleptidae, Nemastomatidae, Trogulidae) this fusion results in a dorsal “scutum,” the component parts of which cannot easily be distinguished. The cephalothorax is often surmounted by a turret—usually grooved dorsally, and beset on its edges with a spiny armature— on the sides of which are the two simple eyes. The position and shape of this turret and the arrangement of its spines are of importance in the classification of the group. In the Trogulidae the base of the turret gives rise to a re- markable, forwardly-directed, bifurcate structure, furnished with numerous strong tubular bristles. This is called the “hood,” and its hollowed- out under surface forms a chamber, the “ camerostome,” in which he the basal joimts = of the pedipalpi. oe In most European Phalangids the under surface of the cephalothorax is 30)\ almost entirely concealed by the forwardly Fie, 230.—Hood of Meto- projecting portion of the abdomen bearing Oe aE tie one generative opening, and by the gnatho- bases, not only of the pedipalpi, but of the first and sometimes of the second legs. As in Spiders, however, there is always present a “sternum” and generally a “labium.” The sternum XV It EXTERNAL FEATURES 44.3 is long and narrow in the Mecostethi, and Cyphophthalmi, but in the Plagiostethi, which include most of the forms found in temperate regions, 1t 1s very short Se and transverse, and is hidden by y)- _pre-Ep. Seg : : es the abdominal prolongation before mentioned. mn The anterior wall of the mouth is formed by a beak-like plate, the “epistome,’ the basal portion of which -is covered externally by a second plate, for which Simon! pro- poses the name “ pre-epistome.” In some Phalangids there are three li se Wes 7 et ee little Fic. 231.—Mouth-parts of Phalan- chitinous plates, one median and two gium. A, B, C, Gnathobases of lateral, on the clypeus, between the pedipalp and first and second legs : ch, chelicera ; ep, epistome ; anterior border of the carapace and lab, labium; m, mouth ; ped, the insertion of the chelicerae. They — Peuipalr : pre-ep, pre-epistome ; 4 st, sternum, shown by the removal are best seen in Nemastoma. of the anterior part of the genital The abdomen always presents Aotted li Daa ham aar Wha dotted line ; 1, 2, 3, 4, legs. evidences of segmentation, though there is a difference of opinion as to the number of segments of which it is composed. This is due to the already mentioned partial or complete fusion of the anterior segments with the cephalothorax. From the admirable researches of Hansen and Sorensen ? it seems likely that the normal number of abdominal segments is ten. Ventrally, the abdomen is produced forward into a “sternal process” which is capped by a genital plate, hardly distinguishable in the Phalangidae, but readily visible in the other families, which surrounds and masks the unpaired genital orifice. Two stigmata or breathing pores are situated on the sides of the first ventral plate, which these authors consider to be composed of two fused sternites. As in other Arachnids there are six pairs of appendages articulated to the cephalothorax. They are the chelicerae, the pedipalpi, and the four pairs of ambulatory legs. The chelicerae are three-jointed and chelate, the second joint having its inner portion produced into an apophysis to which the final joint is apposed. In certain forms (Gonyleptidae, 1 Arachnides de France, vii., 1879, p. 122. 2 On two Orders of Arachnida, Cambridge University Press, 1904. 444 ARACH NIDA—PHALANGIDEA CHAP. Ischyropsalis) the chelicerae are remarkably long, and may considerably exceed the total length of the trunk. The pedipalpi are six-jointed, possessing coxa, trochanter, femur, patella, tibia, and tarsus. They are leg-like and are never chelate, but in some forms terminate in a single movable claw. The coxal joints are provided with maxillary plates. The legs are normally seven-jointed, as in Spiders, the penultimate joint being the metatarsus. The tarsus is always multi-articulate, the number of its joints being variable. It bears terminally one or two simple claws. “ False articulations ” (where the parts are not inserted one into the other, but are only marked off by a membranous ring) are of frequent occur- rence in the legs of these creatures. The first legs, like the pedipalps, bear maxillary plates, as do also the second in most Phalangids. The maxillae of the second legs are, however, entirely absent in Nemastoma, and rudimentary in the Gony- leptidae and the Ischyropsalidae. The coxae of the legs are all largely developed, but are not capable of free motion, being soldered to, and practically forming part of, the cephalothoracic floor. In some forms they are only separated from one another by sight grooves. The extreme length of the legs, and their hard and _ brittle nature, are characteristic features of the Phalangids, though in some species (Trogulidae) they are com- paratively short. The first pair of legs are always the shortest, and the second the longest. The sexual organs of Phalangids are ordinarily concealed, and the sexes can only be distinguished by certain very variable secondary characters, the males being usually smaller of body and longer of leg than the females, besides being more distinctly coloured and being armed with more numerous and longer spines. Sometimes the male chelicerae are highly characteristic. Phalangids are usually destitute of spinning organs, but such have been discovered, in a rudimentary state, in the Cyphoph- thalmi, which are said to spin slight webs. Internal Structure——In Phalangium the mouth leads up- wards into a membranous pharynx, wider than that of Spiders, but narrowing into an oesophagus which passes between the cerebral and thoracic ganglionic nerve-masses. It then turns backwards over the thoracic ganglion, being slightly dilated at XVII ANATOMY 445 that point. Immediately afterwards it dilates into a flask-like gastric sac which occupies almost the whole width of the abdomen, and proceeds straight to the anus. Viewed from above, the shape of this sac is entirely concealed by the large number of caeca (thirty) to which it gives rise dorsally and laterally. The two largest of these caeca extend, parallel to each other, over the whole of the abdominal portion of the gastric sac, and are flanked by four lateral pairs of smaller caeca, while there is a cluster of small caeca covering the anterior and narrower portion of the flask-like stomach. The large hepatic mass so conspicuous on opening dorsally the abdomen of a Spider is here entirely absent, but its functions are believed to be performed by certain wrinkled, tubular, longi- tudinally parallel bodies, about seven in number, closely applied to the wnder surface of the flask. The masticating portions of the maxillae of the pedipalpi and the first pair of legs are hollow distensible sacs, often seen in a swollen condition in specimens kept in spirits. They are furnished, on the inner surface, with a horny ridge. Owing to the fixity of the coxae of the legs, their maxillary plates are incapable of much lateral motion, but are rubbed against each other vertically. Beyond the fact that the heart is a dorsal tube lying along the anterior two-thirds of the alimentary canal, and divided by constrictions into three well-marked and equal portions, little is known of the blood-system of these animals. It is probably essentially like that of Spiders, but the presence of a pericardial sac has not yet been established, nor has the course of the blood- vessels been described in detail. As in other Arachnids, the principal ganglionic nerve masses closely embrace the oesophagus. Immediately anterior to it, forming a conical mass with its base on the oesophagus, is the cerebral ganglion, while just behind it is the transverse portion of the large thoracic nerve-centre. In Phalangiwm opilio, accord- ing to Tulk,! a median nerve is given off from the apex of the cerebral mass (the paired nature of which is apparent) and bifur- cates to the two eyes. Two lateral nerves proceed to certain organs near the origin of the second pair of legs, which were thought by the old writers to be lateral eyes, but which are now 1 Mag. Nat. Hist. (i.), xii., 1848, p. 325. 446 ARACHNIDA—PHALANGIDEA CHAP. known to be glands for the manufacture of the odorous fluid which these animals can exude. The thoracic ganglion expands, on either side of the oeso- phagus, into a mass which extends nearly as far forward as the apex of the cerebral ganglion. These lateral masses give off nerves to the appendages. From the back of the transverse portion proceed three nerves. The median nerve passes above the generative organs, and soon branches into two nerves which presently swell out to form gangha of considerable size, beyond which they soon join again and give off an anasto- mosing net-work of nerve-fibres. The lateral nerves immediately branch. The outer branch Fia. 232.—Nervous and respiratory systems dilates into a ganglion which of a Phalangid. Nerves black, tracheae supphes the external part of ooo white. c.g, Cerebral ganglion; y’, g’,9"”, : : ganglia supplying viscera ; m.n, median the generative organ. The abdominal nerve ; oe, passage for oeso- inner branch, which is longer, phagus ; st, stigma ; ¢h.g, thoracic gang- . Ss lion ; ¢7, main trunk of tracheae. also forms a ganglion the nerves from which are chiefly distri- buted to the under surface of the alimentary canal. The respiratory organs consist of two large tracheal tubes with numerous branches, having their external openings or “stigmata” near the base of the fourth pair of legs. The two main tubes are directed forwards, and are mainly concerned with supplying the largely developed muscles of the legs. The dis- tribution of branches to the abdomen is comparatively feeble. The particular arrangement of tubes in P. opilio, according to Tulk, may be seen in the accompanying figure. There are a pair of coxal glands, of excretory function, opening in the neighbourhood of the coxae of the third pair of legs. — The Phalangidea are remarkable among Arachnids in the possession of large protrusible external organs of generation. The ovipositor of the female may be as long as the whole body of the animal, and the intromittent organ of the male is of XVII CLASSIFICATION 447 almost equal length. The pedipalpi take no part in the fertilisa- tion of the female, which is accomplished directly. The protrusible organs are concealed under the forwardly- projecting anterior segment of the abdomen beneath, the genital orifice being thus in many cases quite near the head-region. The internal sexual organs are not very complex. The ovary re-enters upon itself, forming a ring, and from the point of re-entry a tube proceeds towards the centre of the ring, dilating to form an ovisac. It then narrows, turns forward, tenes once more into a second ovisac, from which the oviduct proceeds to the base of the ovipositor. This is a flattened organ, grooved on its upper surface and bifid at its extremity. The testis of the male is a single sac-like gland, from either end of which proceeds a vas deferens, which, after several convolutions, unite into a sperm-sac which opens at the base of the penis. Partial hermaphroditism is a very frequent phenomenon among the Phalangids, the testis often producing ova as well as spermatozoa. Though the males fight fiercely at the breeding time, the animals on the most part live peacefully together. Henking! found that the eggs of Liobunum, which were about half a millimetre in diameter, were laid during October and hatched out in the following April. Classification.—The Order Phalangidea is divided into three Sub-orders : 1, CYPHOPHTHALMI; 2, Muco OSTETHI ; 3, PLAGIOSTETHI. Sub-Order 1. Cyphophthalmi. Phalangids with dorsal and ventral scutum, only the last abdominal segment remaining free. Eyes two or absent. Maxillary lobe on coxae of first pair of legs rudimentary. Sternum long and narrow. Anterior segment of abdomen not projecting ventrally beyond the coxae of the fourth pair. Odoriferous glands open on prominences. In 1875 Stecker published a description of a remarkable creature which he said he had found in Bohemia, and which he named Gibocellum sudeticum. Among other points it possessed four eyes and four spinning mammillae, and it differed so much from other Cyphophthalmi as to necessitate the foundation of a ' Zool. Jahrb, iii., 1888, p. 319. 448 ARACH NIDA——PHALANGIDEA CHAP. family, Gibocellidae, for its reception. No one else appears to have seen the animal, or any of Stecker’s preparations of it, and Hansen and Sorensen ' adduce grave reasons for believing that it never existed at all. If this species is to be disallowed, the Cyph- ophthalmi all fall into a single family. Fam. Sironidae.—These somewhat Mite- like Phalangids are rarely met with, partly, no doubt, because of their retiring habits and small size, the known forms ranging Fic. 233.— Parasiro from 6 mm. to less than 2 mm. in length. uence Of the seven genera which have been estab- lished, Séylocellus numbers eight species from Borneo and Sumatra, and Pettalus two species from Ceylon. Ogovia, Miopsalis, and Purecellia have one species each, from South Africa, Further India, and the Cape, respectively. The only European forms are the two species of Sivo (France and Austria), and Parasiro corsicus. No species has yet been found in England. Sub-Order 2. Mecostethi.” (LANIATORES). Sternum long and narrow. Dorsal scutum leaving at least the last three segments free. Openings of odoriferous glands not on prominences. The fourth pair of legs usually long and powerful. One terminal claw on each of the first two pairs of legs; two on the last two pairs. The Mecostethi are essentially tropical forms, though a few representatives are found in the caves of Southern Europe. One family (Phalangodidae) has its headquarters in the hot regions of the Old World, while the other two (Cosmetidae, Gonyleptidae) are confined to Central and South America. Fam. 1. Phalangodidae.— Body piriform or triangular, broadest behind. Last ventral segment of abdomen much the largest. Very narrow sternum. Eye-turret near anterior border of cephalothorax. Chelicerae narrow at base. Pedipalpi long and strong. Maxillary plates on first pair of legs rudimentary. No stigmata visible. The only European forms of this family belong to the genus ele. app.t01 10. * Long sternum (ujKos=length ; «7700s =breast). XVII CLASSIFICATION 449 Phalangodes. Theyall avoid the light,and are usually found in caves. Simon ' records six species found in France. A North American species, P. armata, is entirely destitute of eyes. The family has representatives in Australia and in tropical Africa and Asia. Mermerus, Epidanus, Maracaudus, and Sitalces are some of the exotic genera. The other two families of this Sub-order— Fam. 2, Cosmetidae; Fam. 3, Gonyleptidae— include a large number of species, some of con- siderable size (up to an inch in length of body), found in Central and South America. Sub-Order 3. Plagiostethi.” (PALPATORES ) Fic. 234.—Phalan- Hee godes terricola, enlarged. (After First abdominal segment produced forward Simone) ventrally to the level of the first pair of legs, bringing the mouth and the genital opening very near together. Sternum consequently much reduced. Pedipalpi thin, with terminal claw absent or rudimentary. Terminal claws of the legs single. The Plagiostethi include most of the Harvestmen of temperate regions, the most familiar examples of these creatures belong- ing to the large family Phalangidae, and being much more in evidence than the slow-moving and ground-living forms in- cluded in the other families. Fam. 1. Phalangiidae.—Hye-turret always far removed from anterior border of cephalothorax. Second pair of legs with well- marked maxillary lobes. Legs similar, without the false joint called “trochantin.” Multiarticulate tarsi. Simple pedipalpi, with tarsus much longer than tibia, and possessing terminal claw. Some have soft, some coriaceous integuments. The Phalangidae fall naturally into two groups or sub-families, named by Simon ScLEROSOMATINAE and PHALANGIINAE. The first. group consists of more or less coriaceous forms living among moss and herbage. They are not very numerous, there being only about twelve known European species divided among the three genera, Sclerosoma, Mastobunus, and Astrobunus. 1 Arachnides de France, vii., 1879. 2 Transverse sternum (m)\dy.os = transverse). VOL. IV 2G 450 ARACHNIDA—-PHALANGIDEA CHAP, Two species of Sclerosoma are found in England, S. guadri- dentatum occurring not uncommonly among moss or under x ; stones in various parts of the ‘ “oe country. Its back is studded with wart-lke tubercles, which give it a characteristic’ appear- ance. The PHALANGINAE are soft- bodied Harvestmen, always with long legs, which in the genus Liobunum attain an inordinate length. There are nine European genera, Liobunum, Prosalpia, Gyas, Oligolophus, Acantholo- Fia, 235.—Sclerosoma quadridentatum. ( fe OED ae Ds (After Pickard-Cambridge.) Platybunus, and Megabunus, comprising in all about fifty species. Five of these genera are represented in England. The familiar Phalangids, with small, almost spherical bodies and ridiculously long legs, belong to the genus Liobunum, L. rotundum being the common species. It is mature in autumn, when it may be seen scampering at a great pace among the herbage. It very readily parts with its limbs, and Pickard- Cambridge’ relates that he once “saw one running with very fair speed and facility, having lost all but two_ legs, an anterior one on one side and a posterior one on the other.” The Harvestmen so frequently seen on walls belong, as a rule, to the genus Phalangium. The best known example is Phalangium opilio (the P. cornutum of Linnaeus), the male of which possesses a remarkable development of the chelicerae. The genus Oligolophus is well represented in this country, nine species having been recorded. They do not differ greatly from Phalangium, but have, as a rule, more massive bodies, and rather stout, though tolerably long legs. The largest English Harvest- man, not rare under stones at Cambridge, is 0. spinosus, whose body measures half an inch in length. 0. agrestis is perhaps the commonest British Phalangid, and is abundant im woods and among herbage, and on low trees. 1 Monograph of the British Phalangidea, Dorchester, 1890. XVII CLASSIFICATION AIS A Platybunus has two, and Megabunus one British representa- tive. They are of small size, and are to be sought for among heather or dead leaves . in. spring or early \ summer, 1 Fam. 2. Ischyro- psalidae. — Coriaceous Phalangids, with eye- turret far removed from anterior border of cephalothorax. Max- illary lobes of second war “of legs ~~ rudi- mentary, in the form of tubercles. .. Legs similar, without “ tro- chantin.” Multiarticu- ? late tarsi. Tarsus of 7 pedipalp without claw, and shorter than meta- tarsus. Pedipalps long and horizontal. This family includes i a small number of / large or moderate-sized Phalangids, which are found occasionally in thick moss, or in caves, in mountainous regions of the south of Europe, and belong to the genera Jschyropsalis and Sabacon. There is a North American genus, 7'aracus. Fam. 3. Nemastomatidae.—Coriaceous Phalangids, with cephalothorax fused with the first five segments of the abdomen, forming a scutum. Eye-turret near anterior border. No maxillary lobe on second coxae. Similar legs, without “ trochantin.” Multi- articulate tarsi. Tarsus of pedipalp without claw, and shorter than metatarsus. There is but one genus, Wemastoma, in this family, and the members of it are, as a rule, rather small and dark Phalangids, which live under stones or in moss or débris, and are found in Fria. 236.—Oligolophus spinosus. (After Pickard-Cambridge. ) 452 ARACHNIDA——-PHALANGIDEA CHAP. the mature state at all seasons of the year. There are about twenty European species, but only two of these, WV. dugubre and NV. chrysomelas, have as yet been found in Britain. WV. lugubre is a very common animal, and though it does not obtrude itself upon public notice, its lttle black body with two pearly white spots must be a familiar object to all insect collectors who have occasion to search under stones or among moss in damp places. Its legs are short and stout, but those of N. chrysomelas, which is a_ brighter coloured Harvestman with spots of dull gold colour, are long and slender. Fam. 4. Trogulidae. — Coriaceous and very hard integument. Anterior part of cephalothorax pro- duced into a bifurcate “hood.” Often a “ trochantin.” The Trogulidae are very slow-moving Phalangids of moderate or large size (a sixth to half an inch in body), found under stones or in damp moss and débris. They are Mite- like in general appearance, and may readily be distinguished from all other Harvestmen by the presence of the “ hood” (Fig. 230, p. 442), the hollowed-out under surface of which forms a chamber, called by Simon the “ camerostome,” in which he the basal portions of the pedipalps. Only a single immature specimen has been found in England, belonging probably to the species Zvrogulus tricarinatus. It was found in Dorsetshire. Some members of the family are not uncommon in various regions of the Continent. There are four genera, Dicranolasma, Anelasmocephalus, Calathocratus, Fie, 238. — Trogulus y : aquaticus. a, Hood. and Trogulus. Two other genera, Amopaum and (After Simon.) Metopoctea, have been established, but the former is probably the young of Dicranolasma and the latter of Trogulus. According to the monograph on the British Phalangidea by the Rev. O. Pickard-Cambridge, cited above, the following species have been recorded in this country. They all fall under the sub-order Plagiostethi :— Fria. 237.—Nemastoma lugubre. XVII BRITISH HARVEST-SPIDERS igs BRITISH PHALANGIDEA. PHALANGITIDAE, Sclerosoma quadridentatum, Cuvier. 9 romanum, L. Koch. Liobunum rotundum, Latr. ee blackwallii, Meade. Phalangium opilio, Linn. x parietinum, De Geer. - sawatile, C. Ii. Koch. 3 minutum, Meade. Platybunus corniger, Meade. ‘ triangularis, Herbst. Megabunus insignis, Meade. Oligolophus morio, Fabr. 35 alpinus, Herbst. ‘: cinerascens, C. L. Koch. ss agrestis, Meade. 3 tridens, C. L. Koch. v palpinalis, Herbst. 5 ephippiatus, C. L. Koch. <3 sptnosus, Bose. NEMASTOMATIDAE. Nemastoma lugubre, Miller. = chrysomelas, Hermann. TROGULIDAE. Anelasmocephalus cambridgit, Westwood. Trogulus tricartnatus, Viinn. CHAPTER XVIII ARACHNIDA EMBOLOBRANCHIATA (CONTINUED)— ACARINA— HAR- VEST-BUGS——PARASITIC MITES——TICKS——-SPINNING MITES—— STRUCTURE——METAMORPHOSIS——CLASSIFICATION Order IX. Acarina (Acari, Acaridea). Arachnids with unsegmented,' non - pediculated abdomen. Respiration by tracheae, or by the general surface of the body. Mouth parts suctorial, but frequently capable of biting or piercing. Metamorphosis always observable. THE Acarina or Mites are remarkable not so much for the number of their species, ‘which is very considerable, as for the vast multitude of individuals of the Order, which is far in excess of that of any other Arachnid group. This fact is correlated with their minute size. Very few Mites exceed half an inch in length, while very many are microscopic creatures, often measuring less than the hundredth of an inch. Taken all round, a millimetre may be considered a large size for a Mite. There is much variety of habit within the Order. All Mites live principally on fluid nutriment, but it may be obtained from living animals or plants or from decaying organic matter. Some are entirely parasitic upon plants or animals; others attach themselves to animals in their larval stage, but are free when adults; while others, again, live an entirely independent and predaceous life. The greater number of the Mites are too small to strike the eye. Some of them have, however, contrived to attract attention, In no very agreeable manner. Every one knows the Mite popularly called the “ Harvest-bug,” but to this day there is some uncertainty as to 1 The single exception is Optlioacarus, see p. 473. 454 CHAP. XVIII - HARVEST-BUGS APIKE NS) 455 its identity. It was described as a separate species under the name of Leptus autumnalis, and Mégnin was the first to show that it was the larval form of one of the Trombidiidae (see p. 472). Most authors have considered it the larva of 7rombidiuwm holosericeum, but Murray referred it to the genus Zetranychus. The difficulty is that the minute creature cannot be removed from its victim without such injury as to prevent it from being bred out and the mature form determined. Brucker ' has recently compared a large number of “ Harvest-bugs” taken from human beings with the figures and descriptions of the larvae of certain Trombidiidae given by Henking and Berlese, and he determined them as the larvae of 7. gynopterorum. Quite possibly, however, more than one genus is concerned in the production of this pest. That certain skin-diseases are due to Mites (Demodicidae, Sarcoptidae) is a fact which is widely known. ‘The fruit-grower, too, has to take cognisance of the Order, for his trees may suffer from “ Red-spider” (7etranychus telarius), and his black-currant bushes fail under the attack of the “ Gall-mite” (Hriophyes or Phytoptus ribis). The curious swellings or galls which disfigure the leaves of many trees are sometimes of insect origin, but they are often due to Mites. Domestic pets suffer greatly from Acarine parasites. 5 magnified. A, Demodex follicu- to swelling and distortion. Ae Eriophyes (Phyptop- Pam. 2. Demodicidae.——The = = single genus Demodex which constitutes this family consists of a few species of microscopic Mites which inhabit the hair-follicles of mammals, and are the cause of what is known as “ follicular mange,’ some other forms of mange being due to members of the succeeding family. Demodea possesses eight short, three-jointed legs, each terminated by two claws. The abdomen is much produced, and jis transversely striated. About ten species have been described, but of these five are probably varieties of D. folliculorum (Fig. 240, A), which infests Man. Sub-Order 2. Astigmata. The Astigmata are Mites of more or less globular form, with chelate chelicerae and five-jointed legs. All members of the group are eyeless. Their habits arevery various, some feeding on vegetable matter and others on carrion, while a large number are parasitic on animals. Tracheae are absent. There is only one family. VOL. IV 2 H 466 ARACHNIDA—ACARINA CHAP. Fam. 1. Sarcoptidae.—No tracheae or stigmata. Apical rostrum. Oviparous or ovoviviparous. The seventy genera and 530 odd species of this family are divided into a number of sub-families, of which the principal are the Sarcoptinae, the Analgesinae, and the Tyro- elyphinae. (i.) The Sarcoptinae are the so-called “ Itch- mites.” They are minute animals, with bodies transversely wrinkled and legs terminating in suckers or bristles. The genus Sarcoptes, which includes about fifteen species, lives in tunnels which it burrows in the skin of mammals. Gi.) The Analgesinae are the “ Birds’- feather Mites.” The principal genera are Pterolichus (120 species), Pteronyssus (33 species), Analges (23 species), Megninia (42 species), and Alloptes (33 species). (iii.) The Tyroglyphinae ' have received the popular name of “ Cheese-mites,” from the best known example of the group. They are smooth-bodied, soft-skinned white Mites, with legs usually terminating in a single claw, sometimes accompanied by a sucker. They are for the most part carrion-feeders, living Fig. 241.—A, Leg of @ ypon decaying animal or vegetable matter, fowl infested with ee ; ‘“leg-scab” ; B, but a few are parasitic on mammals, insects, female of Sarcoptes and worms. mutans, greatly magnified. (After There are sixteen genera, including about Saat, fifty species. T'yroglyphus siro and T. longior are common Cheese-mites. Other species live in decaying vegetables and food-stuffs. Some of the genus Glycyphagus (G. palmifer, G. plumiger) are very remarkable for the palmate or plumose hairs which decorate their bodies. The remarkable hypopial stage in the development of Tyroglyphus has been mentioned on. p. 463. The Tyroglyphinae are the lowest of the free-living Acarine forms. i aut AA = * MPL rie! ¢ rie Ps ta * y ; + CHAPTER XXI PYCNOGONIDA ! REMOTE, so far as we at present see, from all other Arthropods, while yet manifesting the most patent features of the Arthropod type, the Pyenogons constitute a little group, easily recognised and characterised, abundant and omnipresent in the sea. The student of the foreshore finds few species and seldom many individuals, but the dredger in deep waters meets at times with prodigious numbers, ~ a lending a character to ! the fauna over great areas. The commonest of our native species, or that at least which we find the oftenest, is Pycnogonum littorale (Phalangiwm lit- torale, Strom, 1762). We find it under stones near low-water, or often clinging louse-like to a large Anemone. The squat segmented trunk carries, on four pairs of strong lateral processes, as many legs, long, robust, eight-jointed, furnished each with a sharp terminal claw. In front the trunk bears a long, stout, 1G. 262.—Pycnogonuim littorale, Strom, x 2. ' Pycnogonides, Latreille, 1804 ; Podosomata, Leach, 1815 ; Pychnogonides ow Crustacés aranéiformes, Milne-Edwards, 1834; Crustacea Haustellata, Johnston, 1837 ; Pantopoda, Gerstaecker, 1863. 501 502 PYCNOGONIDA CHAP, tubular proboscis, at the apex of which is the mouth, suctorial, devoid of jaws; the body terminates in a narrow, lmbless, unsegmented process, the so-called “abdomen,” at the end of which is the anal orifice. The body-ring to which is attached the first pair of legs, bears a tubercle carrying four eye-spots ; and below, it carries, in the male sex, a pair of small limbs, whose function is to grasp and hold the eggs, of which the male animal assumes the burden, carrying them beneath his body in a flattened coherent mass. In either sex a pair of sexual apertures open on the second joints of the last pair of legs. The integument of body and limbs is very strongly chitinised, brown in colour, and raised into strong bosses or tubercles along the middle line of the back, over the lateral processes, and from joint to joint of the limbs. The whole aninal has a singular likeness to the Whale-louse, Cyamus mysticeti (well described by Fr. Martins in 1675), that clings to the skin of the Greenland Whale as does Pycnogonum to the Anemone, a resemblance close enough to mislead some of the older naturalists, and so close that Linnaeus, though in no way misled thereby, named it Phalangium balaenarum. ‘The sub- stance of the above account, and the perplexity attending the classification of the animal, are all included in Linnaeus’s short description :' “Simillimus Onisco Ceti, sed pedes omnes pluribus articulis, omnes perfecti, nec plures quam octo. Dorsum rubrum, pluribus segmentis; singulis tribus mucronibus. Cauda cylin- drica, brevissima, truncata. Rostrum membranaceum, sub- subulatum, longitudine pedum. Genus dubium, facie Onisci ceti; rostro a reliquis diversum. Cum solo rostro absque maxillis sit forte aptius Acaris aut proprio generi subjiciendum. . . . Habitat in mari norvegico sub lapidibus.” * 1 Syst. Nat. ed. xii. 1767, vol. ii. p. 1027. * Briinnich’s description (‘‘ Entomologia,” 1764), is still more accurate, and is worthy of transcription as an excellent example of early work. “Fig. iv. Novum genus, a R[ev.] D[om.] Strom inter phalangiis relatum, Sindm. Tom. i. p. 209, t. 1, f.17. Exemplar hujus insecti, quod munificentia R. Autoris possideo, ita describo ; Caput cum thorace unitum, tubo 6 excavato cylindrico, antice angustiore, postice in thoracem recepto, prominens ; Oculiiv. dorsales, a, in gibbositate thoracis positi; c, Antennae 2 tubo breviores moniliformes, subtus in segmento thoracis, cui oculi insident, radicatae ; segmenta corporis, excepto tubo, iv., cum tuberculo e medio singuli segmenti prominulo. Pedes viii., singuli ex articulis vii. xO GENERAL STRUCTURE 503 The common Pycnogonum is, by reason of the suppression of certain limbs, rather an outlying member than a typical repre- sentative of the Order, whose common characters are more strikingly and more perfectly shown in species, for instance, of Nymphon. Of this multiform genus we “have many British species, some of the smaller being common below tide-marks, creeping among weeds =. or clinging like Cap- ae rellae with skeleton SY, limbs to the branches a, of Zoophytes, where their slender forms are not easily seen. In contrast to the stouter body and hmbs of Pycnogonum, the whole fabric of Nymphon tends to elongation ; the body is drawn out so that the successive lateral processes stand far apart, and a slender tween the oculiferous ‘ tubercle and the pro- see bosecis; the legs are produced to an amazing length and an extreme fi) degree of attenuation : i “mirum tam parvum — ~ corpus regere tam a} magnos pedes,” says Fic. 263.—Dorsal view of Nymphon brevirostre, a, Hodge, x 6. Britain. neck intervenes _ be- I Linnaeus. Above the base of the proboscis are a pair of three-jointed appendages, the two terminal joints of which compose a forcipate claw ; below and behind these come a pair of delicate, palp-lke brevissimis compositi, ungue valido terminati. Ex descriptione patet insectum hoe a generibus antea notis omnino differre, ideoque novum genus, quod e crebris articulationibus Pyenogonum dico, constituit.” The confusion between Cyamus and Pycnogonum seems to have arisen with Job Baster, 1765; cf. Stebbing, Anow- ledge, February 1902, and Challenger Reports, ‘‘ Amphipods,” 1888, pp. 28, 30, ete. 504 PYCNOGONIDA CHAP. limbs of five joints; and lastly, on the ventral side, some little way behind these, we find the ovigerous legs that we have already seen in the male Pycnogonum, but which are present in both sexes in the case of Nymphon. At the base of the claw which terminates each of the eight long ambulatory legs stands a pair of smaller accessory or “auxiliary” claws. The genera- tive orifices are on the second joint of the legs as in Pycnogonum, but as a rule they are present on all the eight legs in the female sex, and on the two hindmost pairs in the male. One of the Antarctic Nymphonidae (Pentanymphon) and one other Antarctic genus less closely related (Decolopoda) have an extra pair of legs, No other Pyenogon, save these, exhibits a greater number of appendages than Nymphon nor a less number than Pyenogonum, nor are any other conspicuous organs to be discovered in other genera that are not represented in these two: within so narrow limits he the varying characters of the group. In framing a terminology for the parts and members of the body, we encounter an initial difficulty due to the ease with which terms seem applicable, that are used of more or less analogous parts in the Insect or the Crustacean, without warrant of homology. Thus the first two pairs of appendages in Nymphon have been commonly called, since Latreille’s time, the mandibles and the palps (Linnaeus had called them the palps and the antennae), though the comparison that Latreille intended to denote is_ long abandoned ; or, by those who leaned, with Kroyer and Milne - Edwards, to the Crustacean analogy, mandibles and maxillae. Dohrn eludes the difficulty qe Fain he ee by denominating the appendages by below, showing chelo- simple numbers, Le Lt eT ee Ava. ae palps, and oviger- and this method has its own advantages ; but it is better to frame, as Sars has done, a new nomenclature. With him we shall speak of the Pycnogon’s body as constituted of a trunk, whose first (composite) segment is the cephalic segment or head, better perhaps the cephalothorax, and which terminates in a caudal segment or abdomen: the “head” bears the proboscis, the first appendages XX1 BODY AND LIMBS 505 or “chelophores,”’ the second or “palps,” the third, the false or “ ovigerous ” legs, and the first of the four pairs of “ambulatory ” legs. The chelophores bear their chela, or “hand,” on a stalk or scape ; the ambulatory legs are constituted of three coxal joints, a femur, two tibial joints, a tarsus, and a propodus, with its claws, and with or without auxiliary claws. The Body.—The trunk with its lateral processes may be still more compact than in Pyenogonum, still more attenuated than in Vymphon. In a few forms (eg. Pallene, Ammothea, Tanystylum, Colos- sendeis) the last two, or even more, segments of the trunk are A Fic. 265.—A, Colossendeis proboscidea, Sabine, Britain ; B, Aimmothea echinata, Hodge, Britain ; ©, Phozxichilus spinosus, Mont., Arctic Ocean. (The legs omitted.) more or less coalescent. In Rhynchothorax the cephalic segment is produced into a sharp-pointed rostrum that juts forward over the base of the proboscis. The whole body and limbs may be smooth, tuberculated, furnished with scattered hairs, or some- times densely hispid. The proboscis varies much in shape and size. It may be much longer or much shorter than tne body, cylindrical or tumid, blunt or pointed, straight or (e.g. Decolopoda) decurved ; usually firmly affixed to the head and pointing straight forwards ; sometimes (Hurycide, Ascorhynchus) articulated on a mobile stalk and borne deflexed beneath the body. Chelophores.—The first pair of appendages or chelophores are wanting in the adult Pycnogonum, Phoxichilus, Rhyncho- thorax, and Colossendeis.' 1 Hoek, Chall. Rep. p. 15, mentions a specimen of Colossendeis gracilis, Hoek, 506 PYCNOGONIDA CHAP, In Ammothea and its allies they are extremely rudimentary in the adult, being reduced to tiny knobs in Vanystylum and Fic. 266.—A, B, Chelophores of Ascorhynchus abyssi, G.O.S. A, Young; B, adult. (After Sars.) ©, Anterior portion of Ammothea hispida, Hodge, Jersey: late larval stage (= Achelia longipes, Hodge), showing complete chelae. D, Chela of Eurycide hispida, Kr. Trygaeus, and present as small two-jointed appendages in Ammo- thea. in this last, if not in the others also, they are present in complete chelate form in the later larval stages. In Burycide, Ascorhynchus, and Barana they are usually less atrophied, but yet comparatively small and with imperfect chelae, while in some Ascorhynchi (4A. minutus, Hoek) they are reduced to stumps. In Pallenopsis the scape of the chelophore consists of two joints, as also in Decolopoda and some Ascorhynchus: in Nymphon, Frc. 267.—Chelae of species of Nymphonidae: A, Mymphon brevirostre, Hodge; B, Boreonymphon robustum, Bell; C, Chaetonymphon macronyx, G.O.S. ; D, Nymphon elegans, Hansen. Phoxichilidium, Pallene, and Cordylochele of one only; in all ‘furnished with a pair of distinctly three-jointed mandibles ; and the specimen was the largest of the three obtained.” XXI CHELOPHORES, PALPI, ETC, 507 ce these the terminal portion or “hand” forms a forcipate “chela,” of which the ultimate joint forms the “movable finger.” In some species of Vymphon the chela is greatly produced and attenuated, and armed with formidable serrate teeth on its opposing edges ; in others it is shortened, with blunter teeth ; in Boreonymphon robustum the claws are ereatly curved, with a wide gape between. In this last, and in Phowichilidium, the oppos- ing edges are smooth and toothless. In Cordy- Pre, 268. — Proboscis lochele the hand is almost globular, the movable ee finger being shortened down, and half enclosed _ coilis,G.0.8. (After by the other. Sars.) Palpi.—tThe second pair of appendages, or palps, are absent, _or all but absent, in the adult Pyenogonum, Phoxichilus, Phoai- chilidium, Pallene, and their allies. In certain of these cases, eg. Phoxichilidium, a knob remains to mark their place; in others, e.g. Pallenopsis, a single joint remains; in a few Pallenidae a sexual difference is manifested, reduction of the appendage being carried further in the female than in the male. The composition of the palps varies in the genera that possess them. In Nymphon there are five joints, and their relative lengths (especially of the terminal ones) are much used by Sars in defining the many species of the genus. The recently described Paranymphon, Caullery, has palps of six or seven joints. In the Ammotheidae Fig. 269.—Kury- the number of joints ranges from five or six in — ies Tanystylum to nine (as a rule) in Ammothea and stalked pro. Oorhynchus, or ten, according to Dohrn, in certain pe “IS- species of Ammothea. Colossendeis and the Eury- cididae have a ten-jointed palp, which in this last family is very long and bent in zigzag fashion, as it is, by the way, also in Ammothea. The terminal joints of the palp are in all cases more or less setose, and their function is conjecturally tactile. Ovigerous Legs.—Custom sanctions for these organs an inappropriate name, inasmuch as it is only in the males that they perform the function which the name connotes.' They ! As a rare exception, Hoek has found the eggs carried on the ovigerous legs in a single female of Nymphon brevicaudatum, Miers. 508 PYCNOGONIDA CHAP, probably also take some part, as Hodgson suggests, in the act of feeding. In Pycnogonum, Phoxichilus, Phoxichilidium, and their im- mediate allies they are absent in the female; in all the rest wy A B Cc D Fic. 270.—Ovigerous legs of A, Phoxichilus spinosus, Mont. ; B, Phoxichilidium femor- ee Rathke ; C, Anoplodactylus petiolatus, Kr.; D, Colossendeis proboscideus, they are alike present in both sexes, though often somewhat smaller in the female than in the male. They are always turned towards the lower side of the body, and in many cases even their point of origin is wholly ventral. The number of joints varies: in Phowi- chilidium five, Anoplodactylus six, FiG, 271.— Terminal joints of oviger- Phoxichilus seven ; in Paranymphon ous leg of Rhynchothorax medi- _.- : ‘ . . ihe ys COR Oe eight; in Pyenogonum nine, with, in addition, a terminal claw; in the Amuiotheidae from seven (7rygaeus) to ten, without a claw; in Pallenidae ten, with or without a claw ; in Lhynchothorax, Colossendeis, Eurycide, Ascorhynchus, Nymphon, ten and a claw. The appendage, especially when long, is apt to be wound towards its extremity into a spiral, and its last four joints usually possess a peculiar armature, In Rhynchothorax this pene takes the form of a stout toothed tubercle Terminal joints of on each joint; in Colossendeis of several — oviserdus oe ae rows of small imbricated denticles; in ; Nymphon and Pallene of a single row of curious serrate and pointed spines, each set in a little membranous socket. Legs.—The four pairs of ambulatory legs are composed, in all cases without exception, of eight joints if we exclude, or nine XXI AMBULATORY LEGS 509 if we include, the terminal claw. They vary from a length about equal to that of the body (Pycnogonum, Rhynchothorax, Ammothea) to six or seven times as much, perhaps more, in Nymphon and j \ | \ | \ j Fic. 273.—Nymphon strémii, Kr. Male carrying egg-masses on his ovigerous legs. } t=} fo] Lo] fo) Colossendeis, the fourth, fifth, and sixth joimts being those that suffer the greatest elongation. The seventh joint, or tarsus, 1s Fig. 274.—Terminal joints (tarsus and propodus) of legs. 1, Chaetonymphon hirtum, Fabr. ; 2, V. strémii, Kr. ; 3, Nymphon brevirostre, Hodge ; 4, Ammothea echinata, Hodge ; 5, Ascorhynchus abyssi, G.O.S. (All after Sars.) usually short, but in some Nymphonidae is much elongated; the eighth, or propodus, is usually somewhat curved, and usually possesses a special armature of simple or serrate spines. The 510 PYCNOGONIDA CHAP. Fie. 275.—Legs of A, Pallene brevirostris, Johnston ; B, Anoplodactylus petiolatus, Kr. ; ©, Phoxichilus spinosus, Mont. ; D, Oolossendeis proboscidea, Sabine ; E, Ammothea echinata, Hodge, 3. auxiliary claws, sometimes large, sometimes small, lie at the base of the terminal claw in Ammotheidae, Phoxichilidae, in Phoxi- Oe GLANDS St chilidium, in most Pallenidae, in nearly all Nymphonidae. Their presence or absence is often used as a generic character, helping to separate, eg., Pallene from Pseudopallene and Pallenopsis, and Phowxichilidium from Anoplodactylus ; nevertheless they may often be detected in a rudimentary state when apparently absent. The legs are smooth or hirsute as the body may happen to be. aya ® NI meg ~ Fic. 276.—Boreonyinphon robustum, Bell. Male with young, slightly enlarged. Faeroe Channel, Glands.—In some or all of the appendages of the Pycnogonida may be found special glands with varying and sometimes obscure functions. The glands of the chelophores (Fig. 280, p. 522) are present in the larval stages only. They consist of a number of flask-shaped cells ' lying within the basal joint of the appendage, and generally opening at the extremity of a long, conspicuous, often mobile, spine (e.g. Ammothea (Dohrn), Pallene, Tanystylum (Morgan), Nymphon brevicollum and N. gracile (Hoek)). They secrete a sticky thread, by means of which the larvae attach ' Meisenheimer (Zeitsch. wiss. Zool. \xxii., 1902, p. 235) compares these with certain glands described in Branchipus by Spangenberg and by Claus. 512 : PYCNOGONIDA CHAP. themselves to one another and to the ovigerous legs of the male parent. In Nymphon hamatum, Hoek, the several filaments secreted by the separate sacculi of the gland issue separately. In Pyenogonum the spine on which the gland opens is itself prolonged into a long fine filament, and here, according to Hoek, the gland is in all probability functionless and rudi- mentary. Hoek has failed to find the gland in Ascorhynchus, and also in certain Nymphonidae (e.g. Boreonymphon robustum, Bell), in which the young are more than usually advanced at the time of hatching. The gland has also been described by Lendenfeld and others in Phoxichilidium, whose larvae do not cling together but live a parasitic life; in this genus the long spine or tubercle is absent on which the orifice is usually situated, and, according to Lendenfeld, the secretion issues from many small orifices set along the opposing edges of the chela. Of the two species described by Dohrn as Barana castelli and B. arenicola, the former has the spine of inordinate length, more than twice as long as the whole body, chelophore and all; while in the latter (which species rather resembles Ascorhynchus) the spine is altogether absent. In the palps and ovigerous legs of the adult are found glandular bodies of a hollow vesicular form with a simple ning of cells, the vesicle being divided within by a septum with a central orifice, the outer and smaller half opening to the exterior. These glands are probably of general occurrence, but they have been but little investigated. They lie usually in the fourth and fifth joints of the palp, and the third and fourth joints of the ovigerous leg. Hoek describes them in Discoarachne (Tanystylum) as lying within the elongated third joint of the palp, and opening by a sieve-plate at the end of the second joint. In Ammothea (Dohrn) and Ascorhynchus (Hoek) they open on a small tubercle situated on the fifth joint of the palp. In Nymphon, Hoek describes them as opening by a small pore on the fourth joint of the ovigerous leg. Dohrn failed to find them in Pyenogonum, but in Phoxichilus, Phoxichilidium and Pallene he discovered the glands appertaining to the palps, though the palps them- selves have disappeared in those genera; he has found the glands also in Ammothea, in larvae that have not yet attained their fuil complement of legs. The males in nearly all cases are known to possess glands in XXI GLANDS—ALIMENTARY SYSTEM legs the fourth joints or thighs of all the ambulatory legs, and these glands without doubt act as cement-glands, emitting, lke the chelophoral glands of the larvae, a sticky thread or threads by which the eggs and young are anchored to the ovigerous legs. In some species of Vymphon and otf Colossendeis Hoek could not find these, and he conjectures them to be conspicuous only in the breeding season. While in most cases these glands open by a single orifice or by a few pores grouped closely together, in Barana, according to Dohrn, and especially in b. arenicola, the pores are distributed over a wide area of the femoral joint.’ In Discoarachne (Loman) and Trygaeus they open into a wide chitinised sac with tubular orifice. While the function of these last glands and of the larval glands seems plain enough, that of those which oceur in the palps and ovigerous legs of both sexes remains doubtful. In their morphological nature the two groups of glands are likewise in contrast, the former being unicellular glands, such as occur in various parts of the integument of the body and limbs of many Crustacea; while the latter are segmentally arranged and doubtless mesoblastic in origin, lke the many other segmental excretory organs (or coelomoducts) of various Arthropods. By adding colouring matters (acid-fuchsin, etc.) to the water in which the animals were living, Kowalevsky demonstrated the presence of what he believed to be excretory organs in Phoxichilus, Ammothea, and Pallene. These are small groups of cells, lying symmetrically near the posterior borders of the first three body-segments, and also near the bases of the first joints of the legs, dorsal to the alimentary canal.” Alimentary System.—The proboscis is a very complicated organ, and has been elaborately described by Dohrn.’ It is a prolongation of the oral cavity, containing a highly developed stomodaeum, but showing no sign of being built up of limbs or 1 Ortmann, who would unite Barana with Ascorhynchus, observes: ‘‘ Bei dieser Gattung [Ascorhynchus] konnte ich die Kittdriisen beobachten, die bei 4. ramipes mit dem von Barana castelnaudi [castelli] Dohrn, bei A. eryptopygius mit Barana arenicola iibereinstimmen und also die primitivsten Formen der Ausbildung zeigen.” —Zool. Jahrb. Syst. v., 1891, p. 159. 2 Mém. Acad. Sci. St-Pétersb. (vii.), xxxviii., 1892. ® Fauna u. Flora G. von Neapel, iii. Monogr. 1881, p. 46; see also Loman, J.C. C., Tijdschr. D. Ned. Dierk. Ver. (2), viii., 1907, p. 259. VOL. IV 2 L PYCNOGONIDA CHAP, 514 gnathites. The mouth, situated at its apex, is a three-sided orifice, formed by a dorsal’ and two lateral lobes; and hence the proboscis has been assumed by some, on no competent evidence, to be . constituted of a degenerate “pair of appendages and a labrum or upper lip. Each of the three lobes which bounds the mouth shows the following structures: firstly, a lappet of external chitinised integument, overlapping, as the finger-nail overlaps the finger, a cushion-like lip, ridged after the fashion of a fine-cut file in some species, hairy in others, on the inner surface where the three lips meet to close the orifice of the mouth. Below this again is a pro- minent tooth (Fig. 277, mt), supported, as are the lips, by a system of chitinous rods, which are but little developed in the genus here figured, though conspicuous and com- plicated in others. Transverse ridges run across the angles where adjacent lips meet, and the whole mechanism Fic. 277.— Longitudinal constitutes an section through one efficient valve, preventing the escape of ‘“‘antimere"” of the Nowedetood Tl ; ; uke f tl proboscis in Phoxi- SWallowed 1ood. ye greater portion of the chilus — charybdaeus. G, g', Principal and secondary ganglia; /, sieve -hairs; JZ, lip; mt, oral tooth ; WV, NV’, proboscis is occupied by a masticating or triturating apparatus, the oesophageal cavity expanding somewhat and having its walls inner and outer nerve- Gensely covered, in three bands correspond- cords; #, proboscis: ing to the antimeres, with innumerable teeth. (After Dohrn.) = ; ‘ minute spines (i) or needles, sometimes supplemented by large teeth (/) that point forwards somewhat obliquely to the axis of the proboscis.” In the curious East Indian genus Pipetta (Loman) the sucking and sifting mechanism is low down in the proboscis, and the organ is prolonged into a very fine tube, the lips growing together till they leave an aperture of only 007 mm. for the absorption of liquids. ' The dorsal lobe is absent in Rhynchothorax. ’ For a very detailed account of this mechanism, here epitomised in the merest outline, and for an account of its modifications in diverse forms, the student must consult Dohrn’s Monograph (¢. cit. pp. 46-53). XXI PROBOSCIS—-ALIMENTARY SYSTEM 515 In some cases, where the proboscis itself is short, as in Pallene, this mechanism is carried backwards into the fore-part of the body; and, in the latter genus, the narrow oesophagus or” Fic. 278.—Transverse sections through the proboscis of Ph. charybdaeus. A, Anterior, through the principal ganglionic mass (G) ; B, posterior, at the level of the sieve- hairs (1). Coec, Intestinal caeca ; Dil. M, dilator muscles ; 1, inner nerve-ganglion, = — rn ? C + . 7! y oh ta . . 1+] C 7 1 7 with circular commissure ; V’, outer nerve ; 07, chitinous lining of oral cavity ; RM, Ret.M, retractor muscles. (After Dohrn.) which succeeds the masticatory apparatus is lkewise provided with extrinsic muscles. The oesophagus is followed by a long gastric cavity, which sends forth eaecal diverticula into the chelo- phores (when these are present), and four immensely long ones into the ambulatory legs. The caeca are attached to the walls of the limb cavities, especially at their extremities in the tarsi, by suspensory threads ol connective tissue, and the whole 7.5) o79 — tsnevems — eection gut, central and diverticular, is further through the basal joint of the supported by a horizontal septal mem- M4 Teg im Phowichilus charyb- [i daeus, 9. Cut, Cuticle; Hyp, brane, running through body and legs, —_hypodermis ; nt, intestinal cae- hich t hed leplaad 1 cum; JV, nerve-cord; Ov, ovary ; which separates the dorsa 00d-Vesse Sept, septum. (After Dohrn.) and sinus from the gut, the nervous system and the ventral sinus, giving support also to the reproduc- tive glands. A short and simple rectum follows the gastric cavity. In Phowichilus, which lacks the three anterior appendages in the female and the two anterior in the male, two pairs of caeca run from the gut into the cavity of the proboscis (Fig. 278, B, coec.).' 1 Dolign, ¢. cit. p. 55. 5 16 PYCNOGONIDA CHAP. Circulatory System.—The heart has been especially studied by Dohrn in Phovichilus. It consists of a median vessel running from the level of the eyes to the abdomen, furnished with two pairs of lateral valvular openings, and sometimes, though not always, with an unpaired one at the posterior end. The walls are muscular, but with this peculiarity that the muscular walls do not extend around the heart dorsally, in which region its lumen is only covered by the hypodermis and cuticle of the back. The blood-spaces of the body are separated into dorsal and ventral halves by the septal membrane already referred to, which is per- forated in the region of the lateral processes by slits placing the two cavities in communication; this septal membrane runs through the limbs to their tips, and far into the proboscis, where it is attached to the edge of the superior antimere. The blood is a colourless plasma with several kinds of corpuscles, of which the most remarkable are amoeboid, actively mobile, often coalescing into plasmodia. The course of the circulation is on the whole outwards in the inferior or ventral sinus, inwards towards the heart in the superior, save in the proboscis, where the systole of the heart drives the blood forwards in the dorsal channel. The beat is rapid, two or three times in a second, according to Loman, in Phoxichilidium. Especially in the species with small body and exaggerated legs, the movement of the circulatory fluid is actuated more by the movements of the hmbs and the contrac- tions of the intestinal caeca than by the direct impulse of the heart. Nervous System.—The nerve-chain consists of a fused pair of supra-oesophageal gangha, which innervate (at least in the adult) the chelophores, and of ventral ganglia, whence proceed the nerves to the other limbs. The ganglia of the second and third appendages are fused with one another, sometimes also with the gangha of the first ambulatory legs; the ganglia of the three posterior pairs of legs are always independent (though the development of their longitudinal commissures varies with the body-form), and they are succeeded by one or two pairs of ganglia, much reduced in size, situated in the abdomen, of which the posterior one innervates the muscles of the abdomen and of the anal orifice. Each lateral nerve divides into two main branches, which supply the parts above and below the septal membrane. The nerve-supply of the proboscis is very com- XXI NERVOUS SYSTEM—EYES 517 plicated. Its upper antimere is supphed from the pre-oral, its two lateral antimeres from the first post-oral, ganglion, and each of these three nerves divides into two branches, of which the inner bears six to eight or more small ganglia, which annular commissures passing round the pharynx connect one to another. Of these ganglia and commissures the anterior are the largest, and with these the outer lateral nerve-branches of the proboscis merge. The immediate origin of the nerves to the chelophores is from the median nerve that springs from the under side of the supra-oesophageal ganghon to run forward into the proboscis, but it is noteworthy that the chelophores receive twigs also from the lateral nerves of the proboscis which arise from the post-oral ganglia. Eyes.—Eyes are the only organs of special sense known in the Pycnogons. The deep-water Pycnogons, in general those inhabiting depths below four or five hundred fathoms, have in most cases imperfect organs, destitute of lens and of pigment, so imperfect In many cases as to be described as wanting. It is rare for the eyes to be Jacking in shallow-water species, as they are, for instance, in Ascorhynchus minutus, Hoek, dredged by the Challenger in 38 fathoms, but, on the other hand, it is no small minority of deep-water species that possess them of normal character and size, even to depths of about 2000 fathoms, In all cases where eyes are present, they are simple or “monomeniscous ” eyes, four in number, and are situated in two pairs on an “oculiferous tubercle,’ sometimes blunt and low, sometimes high and pointed, placed on the so-called cephalo- thorax, or first, compound, segment of the body. The anterior pair are frequently a httle larger, sometimes, as in Phoxichilidium mollissimum, Hoek, very much larger, than the posterior. The minute structure of the eye has been investigated by Dohrn, Grenacher, Hoek, and Morgan. The following account is drawn in the first instance from Morgan’s descriptions.’ The eye of a Pyenogon (Phoxichilidium) is composed of three layers, an outer layer of specialised ectoderm cells (hypodermis) that secrete the cuticular lens, a middle layer of visual or retinal elements, and an inner layer of pigment-cells. The elements of the middle layer consist of much elongated cells, whose branching outer ends are connected with nerve-fibrils and 1 Biol. Stud. Johns Hopkins Univ. v., 1891, p. 49. pt 8 PYCNOGONIDA CHAP. interwoven in a protoplasmic syncytium, whose middle parts are occupied by the nuclei and whose inwardly-directed ends form the retinal rods or bacilli. The pigment-cells of the inner layer are of various forms, those towards the middle of the eye being small and flattened, those at the sides being, for the most part, long and attenuated, so seeming, as Morgan remarks, to ap- proximate in character to the retinal elements. The pigment layer is easily dispersed and reveals beneath it a median vertical raphe, caused by the convergence of the cells of the middle layer from either side, and along the line of this raphe the optic nerve joins the eye, though its subsequent course to its connection with the retinal elements is obscure. It is at least clear that the retina is an “inverted” retina, with the nerve-connected bases of its cells lying outwards and their bacillar extremities directed inwards. In a longitudinal vertical section of the eye of a larva (Tanystylum), at a stage when three pairs of walking Jegs are present, Morgan shows us the pigment-layer apparently con- tinuous with the hypodermis just below the eye, and in close connection with the middle layer at the upper part of the eye. From this we are permitted to infer a development by invagina- tion, in which the long invaginated sac is bent and pushed upwards till it comes into secondary contact with the hypoderm, so giving us the three layers of the developed eye. This manner of formation is precisely akin to that described by Parker, Patten, Locy, and others for the median eyes of Scorpions and of Spiders, and the organ is structurally comparable to the Nauplius- or median eye of Crustacea. But neither in these cases nor in that of the Pycnogon is the whole process clear, in consequence chiefly of the obscurity that attends the course of the optic nerve in both embryo and adult. For various discussions and accounts, frequently contradictory, of these phenomena, the reader is referred to the authors quoted, or to Korschelt and Heider’s judicious summary.' There seems to be a small structure, of some sort or other, between the ocelli on either side. Dohrn thought it might be auditory, Loman that it might be secretory, but its use is unknown. Integument. — The chitinised integument is perforated by 1 Vergl. Entwickl. d. wirbellosen Tiere, Jena, 1893, p. 664. XXI INTEGUMENT—REPRODUCTIVE ORGANS 519 many little cavities, some of them conical and tapering to a minute external pore, the others more regularly tubular. Some- times, but according to Hoek rarely, the tubular pore-canals communicate with, or arise from, the conical cavities, The pore- canals transmit a nerve for the supply of sensory hairs, often forked, which arise from the orifice of the canal in little groups of two or more, sometimes in rosettes of eight or nine. These setae are small or rudimentary in Ascorhynchus and_ totally wanting in Oolossendeis; they appear to be extremely large and stellate in Paranymphon. The conical cavities contain proliferated epithelial cells, blood-corpuscles, and cells of more doubtful nature that are perhaps glandular. According to Dohrn, glands exist in connection with both kinds of imtegumentary perforations, and he suspects that they secrete a poisonous fluid in response to stimuli affecting the sensory hairs; Hoek, on the other hand, is inclined to ascribe a respiratory function to the cavities; but imdeed, as yet, we must confess that their use is undetermined. Reproductive Organs.—In each sex the generative organs consist of a pair of ovaries or testes lying above the gut on either side of the heart; in the adult they are fused together posteriorly at the base of the abdomen, and send long diverticula into the ambulatory legs. In the female Phowichilidium, at least, as Loman has lately shown, the fusion is complete, and the ovary forms a thin broad plate, spreading through the body and giving off its lateral diverticula. The diverticula of the testes reach to the third joint of the legs, those of the ovaries to the fourth, or sometimes farther. The ova ripen within the lateral diverticula, chiefly, and sometimes (Pallene) exclusively, in the femora or fourth joints of the legs,’ which, in many forms, are ereatly swollen to accommodate them; the spermatozoa, on the other hand, are said to develop both within the legs and within the thoracic portions of the testis. The genital diverticula may end blindly within the leg, or communicate through a duct with the exterior by a valvular aperture placed on the second coxal joint. Such apertures occur, as a rule, on all the legs in the females, in Rhynchothorax and Pycnogonum on the last only. In the males an aperture is present on all the legs in Decolopoda and Phoxichilidium ; on the last three in Nymphon and Phowichilus ; 1 Tn the second joint in Ascorhynchus abyssi, Sars, and A. tridens, Meinert. 520 PYCNOGONIDA CHAP, in most genera on the last two; in Pycnogonum and Rhynchothoraxz on the last only. Very commonly the female individuals are somewhat larger than the males, and in some species (Ammothea, Trygaeus) the latter are distinguished by a greater development of spines or tubercles on the body and basal joints of the legs (Dohrn). The act of fecundation has been observed by Cole’ in Anoplodactylus. The animal reproduces towards the end of August. Consorting on their Hudendrium (Hydroid) colony, the male climbs upon the female and crawls over her head to lie beneath her, head to tail; and then, fertilisation taking place the while, the hooked ovigerous legs of the male fasten into the extruding egg-masses and tear them away. The whole process 1s over in five minutes. The fresh egg-masses are more or less irregular in shape, and white in colour like little tufts of cotton. Each ball of eggs that the male carries represents the entire brood of one female, and in Phowichilidium Loman has seen a male carrying as many as fourteen balls. Fertilisation is external, taking place while the eggs are being laid. The spermatozoa have small rounded heads and long tails, and are thus unlike the spermatozoa of most Crustacea. Development.— Until the hatching of the embryo, the eggs of the Pycnogons are carried about, agglutinated by cement- substance into coherent packets, on the ovigerous legs of the males. They are larger or smaller according to the amount of yolk - substance present, very small in Phowxichilidium and Tanystylum (Morgan), where they measure only ‘05 mm. in diameter; larger in Pallene (25 mm.); larger still (‘5-"7 mm.) in Nymphon. In Pallene each egg-mass commonly contains only two eggs; in the other genera they are much more numerous, rising to a hundred or more in Ammothea (Dohrn). The egg- masses may be one or more on each ovigerous leg, sometimes (Phoxichilidium angulatum, Dohrn) a single egg-mass is held by both legs; they are extremely numerous in Phowichilus, and in Pycnogonum they coalesce to form a broad pad beneath the body. The fact that it is the male and not the female that carries the eggs was only announced in 1877 by Cavanna;? 1 Biol. Bulletin Woods Holl, vol. ii., Feb. 1901, p. 196. 2 Studi e ricerche sui Picnogonidi, Firenze, 1876. LO DEVELOPMENT 521 before, and by some even after lis time, the two sexes were constantly confused.' Segmentation is complete, symmetrical in the forms with smaller eggs, unequal in those burdened with a preponderance of yolk (Morgan). In Padlene, as in the Spider’s egg, what is described as at first a total segmentation passes into a superficial or centrolecithal one by the migration outwards of the nuclei and the breaking down of the inner ends of the wedge-shaped segmentation-cells. The blastoderm so formed becomes con- centrated at the germinal pole of the egg. ‘MONT (ssey 10) OT 6-F 2 “OTIQOW * WVCIAHLOWNY seutds es sf sg i peteqye0g 6 ED My 0 Avequawt pny, a * PYUOUUnT_T ayRllas Arey 9 ut pexeyop pazmatses ‘MOL ao -Iplt efoto “peypeqs ca Mey tray PG TT? AA 7 | wey? omow | 3 ‘? OL OL ‘poytttol-g adeog) ‘aT tqoyy AVAIGIOAY AG pearmnoop SavuTqaTOS adits ‘o[IqouL 7 ‘2 ‘7 ‘L | & ‘e ‘] ‘T | QueoseTeoD ii ‘smor Auvyy | 3 ‘°P OT OL 0 PRL MaMLOG *“UVAILANaUsSso to“) | payutol-z quaoseTRoo ayduuts & *D adeos ‘|]RUS pedmmo Gy ‘2 ‘GL |‘G ‘F ‘eG ‘I| ‘pesuepuog| ¢ ‘sMOd N07 | szutol OT squtol oT ‘oqatdmog -ap ‘poxty * avdldodo 109g —(saeg ‘eqepteyooydAr9) fs) 2 : | ie ean | sSary | ‘op uo yYQeog, Sa Bea AO ‘sd[vg ‘saroydoreayp *stosoqoig "YGINODONOAG ‘ssuruedg [eymey XXI CLASSIFICATION —DECOLOPODIDAE IS seyal CLASS PYCNOGONIDA|! Marine Arthropoda, with typically seven (and very exception- ally eight) pairs of appendages, of which none have their basal joints subservient to mastication, the first three are subject to suppression, the first (when present) are chelate, the second palpiform, the third ovigerous, and the rest form ambulatory limbs, usually very slender and long; with a suctorial proboscis, a limbless, unsegmented abdomen, and no manifest respiratory organs. Fam. 1. Decolopodidae.— Appendage I. dwarfed, but com- Fic. 282.—Decolopoda australis, Bights. A, x 1: from a specimen obtained at the South Shetlands by the Scotia Expedition. B, First appendage, or chelophore. (A, original ; B, after Hodgson.) plete and chelate, scape with two joints; II. 9-10-jointed; III. well developed in both sexes, 10-jointed, the terminal joints with 1 See (inter alia) Dohrn, 7.c. ; E. B. Wilson, Rep. U.S. Fish. Comm. (1878), 1880 ; Hoek, Chall. Report, 1881-; G. O. Sars, Norw. N. Atl. Exp. 1891; Meinert, Lngol/ 532 PYCNOGONIDA CHAP. about four rows of teeth; five pairs of legs, destitute of accessory claws; genital apertures on all the legs (Bouvier). Decolopoda australis, Eights ' (1834), a remarkable form from the South Shetlands, recently re-discovered by the Scotia expedi- tion. The animal is large, seven inches or more in total span, in colour scarlet; it was found in abundance in shallow water and cast upon the shore. The body is greatly condensed, the proboscis is “clavate, arcuated downwards,’ and beset with small spines. A second Antarctic species, D. antarctica, has been described by Bouvier. The presence of a fifth pair of legs distinguishes Decolopoda from all known Pycnogons, except Pentanymphon. Stebbing would ally Decolopoda with, or even include it in, the Nymphonidae; but the presence of a second joint in the chelophoral scape, the number of joints in, and the armature on, the ovigerous legs, and the deflexed proboscis, are all characters either agreeing with or tending towards those of the KEurycididae ; while the Colossendeidae would be very like Decolopoda were it not for the complete suppression of the chelophores. It seems convenient to. constitute a new family for this remarkable form. Fam. 2. Colossendeidae (Pasithoidae, Sars).—Appendage I. absent in adult ; appendage IL. very long, 10-jointed; appendage III. 10-jointed, clawed, with many rows of teeth ; auxiliary claws absent ; segments of trunk fused ; proboscis very large, somewhat mobile ; genital apertures, in at least some cases, on all the legs. Pasithoe, Goodsir (1842), which Sars assumes as the type of the family, is here relegated to Ammothea.’ Colossendeis, Jarszynsky (1870) (Anomorhynchus, Miers (1881), Rhopalorhynchus, Wood- Mason (1873) ), remains as the only genus commonly accepted : large, more or less slender short-necked forms; world-wide, principally Arctic, Antarctic, and deep-sea; about twenty-five species.» The largest species, C. gigas, Hoek, from great depths Exped. 1899; Mobius, Fawna Arctica, 1901, Valdivia Exped. 1902; Cole, Harri- man Alaska Exped. 1904; Hodgson, Discovery Exped. 1907 ; Bouvier, Exp. Antarct. Fr. 1907. 1 Boston Journ. Nat. Hist. i., 1834, p. 203; Cf. Hodgson, Pr. R. Phys. Soc. Edinburgh, xvi., 1905, p. 85; Zool. Anz. xxv., 1905, p. 254; Discovery Exp., ‘*Pyenogonida,” 1907 ; Bouvier, Hxp. Antarct. Fr. 1907. 2 See pp. 535, 541. Cf. Dohrn (é. cit.), p. 228. 3 The first known species was described as Phowichilus proboscideus, Sabine, from the shores of the North Georgian Islands (1821). 3 XXI COLOSSENDEIDAE—EURYCIDIDAE 533 in the Southern Ocean, has a span of about two feet. The North Atlantic C. proboscidea and Antarctic C. australis are very closely related to one another. Carpenter would retain the genus Rhopalorhynchus tor Rh. kréyeri, W.-M. (Andamans), 2. clavipes, Carp. (Torres Straits), and &. tenwissimus, Haswell (Australia), all more or less shallow-water species, excessively attenuated, with the second and third body-segments elongated, the caudal segment excessively reduced, the club-shaped proboscis on a slender stalk, and other common characters. Pipetta weberi, Loman (1904), is a large and remarkable form from the Banda Sea, apparently referable, in spite of certain abnormal features, to this family; the proboscis is extraordinarily long and slender ; the palps have eight joints, the ovigerous legs eleven. Fam. 3. Burycididae (Ascorhynchidae, Meinert).— Appen- dage I. more or less reduced; appendage II. 10-jointed (absent in Hannonia); appendage III. 10-jointed, clawed, with more than one row of serrated teeth; proboscis movably articulated and more or less bent under the body ; auxiliary claws absent. Hurycide, Schiddte (1857) (Zetes, Kroyer, 1845): Appendage I. with two-jointed scape, without chelae in adult ; one species (£. hispida, (Ky.)), from the North Atlantic and Arctic, and two others from the East Indies, recently described by Loman. Sarana arenicola, Dohrn (1881), is nearly allied. Ascorhynchus, G. O. Sars (1876) (Gnampto- rhynchus, Bohm, 1879; Scaeorhynchus, Wilson, 1881), very similar to Hurycide, with which, according to Schimkewitsch, it should be merged, includes large, smooth, elongated forms, with long neck and expanded frontal region, and a long proboscis lacking the long scape that supports the proboscis in Lurycide; about twelve species, world-wide, mostly deep-water. Barana castelli, Dohrn, from Naples is akin to the foregoing genera, but seems to deserve generic separation from B. arenicola. -Ammothea longicollis, Haswell, from Australia, is, as Schimkewitsch has already remarked, almost certainly a Hurycide, as 1s also, probably, Parazetes auchenicus, Slater, from Japan. Hannonia typica, Hoek (1880), from Cape Town, is a remarkable form, lately redeseribed by Loman. The chelophores are much reduced, the palps are absent; the ovigerous legs are Fic. 283.— Hurycide his- pida, Kr. ; side view. 534 PYCNOGONIDA CHAP. 10-jointed, and clawed; the terminal joints of the latter bear long straight spines, scattered over their whole surface; the proboscis is borne on a narrow stalk, and sharply deflexed. The egos form a single flattened mass, as in Pycnogonum. While the lack of palps would set this genus among the Pallenidae, the remarkable proboscis seems to be better evidence of affinity with Ascorhynchus and Eurycide.' Nymphopsis, Haswell (1881), is a genus of doubtful affinities, placed here by Schimkewitsch, The first appendage is well- developed and chelate; the palps are 9-jointed, the ovigerous legs are 7-jointed, none of the joints being provided with the compound spines seen in Vymphon and pre It is perhaps an immature form. Schimkewitsch has described another species, N. korotnevi, and Loman a third, WV. muscosus, both from the East Indies. Fam. 4. Ammotheidae.—Akin to Enurycididae in having the proboscis more or less movably jointed to the cephalic segment, and appendage I. reduced, non-chelate in the adult ; the body is compact and more or less inperfectly segmented ; appendage IT. 4-9-jointed; appendage III. clawless, and the number of joints sometimes diminished, with a sparse row of serrated spines; auxiliary claws usually present. Ammothea, Leach (1815) (meluding Achelia, Hodge (1864) = the old non-chelate individuals): appendage I. very all 2-jointed; appendage I]. 8-9-jointed; caudal segment fused with last body- segment; about eighteen species, four from the South Seas, two or three from the East Indies, the rest mostly Mediterranean and North Atlantic, in need of revision. Ammothea longipes, Hodge, is the young of dAchelia hispida, Hodge ; and Ammothea magnirostris, Dohrn, is apparently the same species. A. fibuli- fera, Dohrn, seems identical with Achelia echinata, Hodge (of which A. brevipes, Hodge, is the young), and so probably is 4. achelioides, Wilson; Hndeis didactyla, Philippi (1843), is very probably the same species. 4. wniunguiculata, Dohrn (? Pariboea spinipalpis, Philippi (1848)), has no auxiliary claws, Leionym- phon, Mobius (1902), contains nine Antarctic forms, allied to Ammothea (including A. grandis, Pfeffer, and Colossendeis gibbosa, Mob., which two are probably identical), with characteristic 1 Pocock (Encycl. Brit., 10th ed., Art. ‘‘ Arachnida’’) makes Hannonia the solitary type of a family. Cf. Loman, Zool. Jahrb., Syst., xx., 1904, p. 385. XXI AMMOTHEIDAE—-RHYNCHOTHORACIDAE 535 transverse ridges on the body, a large proboscis, a 9-jointed palp, and somewhat peculiar ovigerous legs. Ciluneulus, Fragilia, and Scipiolus are new genera more or less allied to Leionymphon, described by Loman (1908) from the Siboga Expedition." Tanystylum, Miers (1879) (including Clotenia, Dohrn (1881), and Discoarachne, Hoek (1880)), has append- age I. reduced to a single joint or a small tubercle, and appendage II. 4-6-jointed; world-wide; about eight species. Austrodecus glacialis and Austroraptus polaris are two allied Antarctic species, described by Hodgson (1907), the former a curious little form with a pointed, weevil-like proboscis, no chelophores, and 6-jointed palp. Zrygaeus communis, Dohrn (1881), from Naples, has a 7-jointed, and Oorhynchus auck- landiae, Hoek (1881), a 9-jointed palp; the former has only seven joints in the ovigerous leg. Lecythorhynchus armatus, Bohm (1879), with rudimentary 2-jointed chelophores, and J. (Corniger) hilgendorfi, Bohm, with small tubercles in their place, both from Japan, have also 9-jointed palps: the former, at least, is apparently an Ammothea. Several insufficiently described genera, Phanodemus, Costa (1836), Platychelus, Costa (1861), Oiceobathes, Hesse (1867), and Béhmia, Hoek (1880), seem to be referable to this group; all have chelate mandibles, and may possibly be based on immature forms. Goodsir’s Pasithoe vesiculosa” is, in my opinion, undoubtedly Ammothea hispida, Hodge, and so also, I believe, is his Pephredo hirsuta; P. umbonata, Gould? (Long Island Sound), is, with as little doubt, Zanystylum orbiculare, Wilson. Fam. 5. Rhynchothoracidae.—The animal identified by Dohrn as Rhynchothorax mediterraneus, Costa (1861), is a minute and very remarkable form, without chelophores, with large 8-jointed palps, reduced by fusion to five joints, and 10-joited, clawed ovigerous legs, which last are provided on the last five jomts with peculiar toothed tubercles. The general aspect of the body is somewhat lke that of an Ammothea, which genus it resembles in the ventral insertion of the ovigerous legs and the somewhat imperfect segmentation of the body. It 1 Loman conjoins all these genera, and also Lecythorhynchus, with Nymphopsis, as a sub-family Nymphopsinae of Ammotheidae. 2 Edinb. New Phil. Journal, Oct. 1842, p. 367 (P. capillata on Plate). 3 Proc. Boston Nat. Hist. Society, vol. i., 1841-44, p. 92. 536 PYCNOGONIDA CHAP, differs from Ammotheidae in the possession of a claw on appen- dage III. It is highly peculiar in the structure of the mouth, in having a long forward extension of the oculiferous tubercle jutting out over the proboscis, in the extreme shortness of the intestinal caeca and ovaries which scarcely extend into the legs, and in the absence of cement-glands from the fourth joint of the legs; these last are present only in the third joint of the pen- ultimate legs. A single pair of generative orifices are found on A B Fic. 284.—Rhynchothorax mediterraneus, Costa. A, Body and bases of legs ; B, terminal joints of palp. (After Dohrn.) the last legs. A second species, F. australis, Hodgson, comes from the Antarctic. Fam. 6. Nymphonidae.— Appendage I. well-developed, chelate; II. well-developed, usually 5- jointed; III. well- developed in both sexes, usually 10-jointed, the terminal joints with one row of denticulated spines. — , Nymphon, Fabr. (1794), about forty-five recognised species, of which some are but narrowly defined. Closely allied are Chaetonymphon, G. O. Sars (1888), including thick-set, hairy species, about eight in number, from the North Atlantic, Arctic, and Antarctic; and Boreonymphon, G. O. Sars (1888), with one species (B. robustum, Bell, Fig. 276), also northern, in which the auxiliary claws are almost absent. Nymphon brevicaudatum, XI NYMPHONIDAE PALLENIDAE 537 Miers (=. horridum, Bohm), an extraordinary hispid form from Kerguelen,’ is also peculiar. Pentanymphon, Hodgson (1904), from the Antarctic (cireumpolar), differs in no respect save in the presence of a fifth pair of legs; one species. The only other genus is Paranymphon, Caullery (1896) (one species, Gulf of Gascony, West of Ireland, Greenland), in which the palp is (6-)7-jointed, the ovigerous leg 8-jointed, and the auxiliary claws are absent. Fam. 7. Pallenidae.—As in Nymphon, but appendage II. absent or rudimentary. Pallene, Johnston (1837): about ten species (Mediterranean, North Atlantic, Arctic, Australia). P. languida, Hoek, Australia, lacks auxiliary claws, and is otherwise distinct ; but P. novaezealandiae, G. M. Thomson, is typical. Pseudopallene, Wilson (1878):° appendage ITI. clawed ; auxiliary claws absent; four (or more) species (North Atlantic, Arctic, Antarctic). P. (Phoxichilus) pygmaea, Costa (1836), and P. spinosa, Quatref., seem to belong to this genus or to Pallene. Cordylochele, G.O.Sars (1888): closely allied, but with front of cephalic segment much expanded and chelae remarkably swollen, includes SS tee) three very smooth, elongated, northern species, to — brevirostris, John- which Bouvier has added one from the Antarctic; PEN Pallene laevis, Hoek, from Bass’s Straits, is somewhat similar. Neopallene, Dohrn (1881): as in Pallene, but with a rudimentary second appendage-in the female, and no generative aperture on the last leg in the male (one species, Mediterranean). Parapallene, Carpenter (1892): as in Pallene, but without auxiliary claws, and with the two last segments of the trunk (which in Pallene are coalesced) independent (about 1 Found by Sir John Ross’s expedition in 1840, and subsequently by the Challenger expedition and other visitors. ° Stebbing has recently shown (Knowledge, Aug. 1902, p. 157) that the genus Phoxichilus was instituted by Latreille (Nowy. Dict. d’hist. nat. 1804) for the Pycnogonum spinipes of Fabricius, now Pseudopallene spinipes, auctt. Hence he changes Pseudopallene to Phowxichilus, Latr., and Phoxichilidae and Phowxichilus, auctt., to Chilophoxidae, etc. ; it also follows that the family known to all naturalists as Pallenidae should, according to the letter of the law of priority, be henceforth known as the Phoxichilidae. In my opinion this is a case where strict adherence to priority would serve no good end, but would only lead to great and lasting confusion (cf. Norman, J. Linn. Soc. xxx., 1908, p. 231). 538 PYCNOGONIDA CHAP. ten species, East Indies and Australia); Pallene grubw, Hoek (Phouichilidium sp., Grube, 1869), is probably congeneric. Pallenopsis, Wilson (1881): appendage I. 2-jointed; appendage II. rudimentary, 1-jointed; appendage III. clawless; auxiliary claws present; slender forms, including some formerly referred to Phoxichilidium; about fifteen species, world-wide. Pallene dimorpha, Hoek, from Kerguelen, with 4-jointed palps, deserves a new generic appellation. P. Jongiceps, Bohm, from Japan, with rudimentary 2-jointed palps in the male, is also peculiar. Fam. 8. Phoxichilidiidae——Appendage I. well-developed ; II. absent; III. present only in the male, having a few simple A B Fic. 286.—Phoxichilidium femoratum, Rathke, Britain. A, The animal with its legs removed ; B, leg and chela. spines in a single row. The last character is conveniently diagnostic, but nevertheless the Phoxichilidiidae come very near to the Pallenidae, with which, according to Schimkewitsch and others, they should be merged; the two families resemble one another in the single row of spines on the ovigerous legs and in the extension of the cephalic segment over the base of the proboscis. Phoxichilidium, M.-E. (1840): appendage ITI. 5-jointed ; five or six species (Mediterranean, North Atlantic, Arctic, Australia, Japan). Anoplodactylus, Wilson (1878): appendage III. 6-jointed; auxiliary claws absent or very rudimentary; about twelve species, cosmopolitan, of which many were first XXI PHOXICHILIDIIDAE—PYCNOGONIDAE 539 referred to Phowichilidium. A. neglectus, Hoek, comes from 1600 fathoms off the Crozets. Oomerus stigmatophorus, Hesse (1874), from Brest, seems to belong to one or other genus, but is unrecognisable. Anaphia, Say (1821), is in all probability identical with Anoplodactylus, and if so the name should have priority. Halosoma, Cole (1904), is an allied genus from California. A Fie. 287.—A noplodactylus petiolatus, Kr., Britain. A, Dorsal view; B, side view. Fam. 9. Phoxichilidae.'— Appendage I. and II. absent; appendage III. present only in the males, 7-jointed, with minute scattered spines; auxiliary claws well-developed; body and legs slender. The only genus is Phowxichilus (auctt., non Latreille, Chilophozus, Stebbing, 1902); the type is P. spinosus, Mont. (non Quatrefages), from the N. Atlantic, and P. vulgaris, Dohrn, P. charybdaeus, Dohrn, and P. laevis, Grube, are all very similar. Endeis gracilis, Philippi (1843), is probably identical with P. spinosus, or one of its close allies. There are also known P. meridionalis, Bohm, P. mollis, Carp., and P. procerus, Loman, from the East Indies; P. australis, Hodgson, from the Antarctic ; P. béhmii, Schimk., of unknown locality; and forms ascribed to P. charybdaeus by Haswell and by Schimkewitsch from Australia and Brazil. Fam. 10. Pycnogonidae.— Appendages I. and II. absent ; appendage III. present only in the male, 9-jointed, with small, simple spines; auxiliary claws absent or rudimentary ; body and legs short, thick-set. The only genus is Pycnogonum, Briinnich (1764) (Polygonopus, 1 Vide note 2, p. 537. 540 PYCNOGONIDA CHAP, Pallas, 1766); the type is P. littorale, Strom, of the N. Atlantic ()-450 fathoms), to which species have also been ascribed forms from various remote localities, e.g. Japan, Chile, and Kerguelen. P. crassirostre, G. O. Sars, a northern and more or less deep-sea form, is distinct, and so also are P. nodulosum and P. pusillum, Dohrn, from Naples. P. stearnsi, Ives, from California, is like P. littorale, except for the rostrum, which resembles that of P. crassirostre. P. magellanicum, Hoek, P. magnirostre, Mobius, both from the Southern Ocean; P. microps, Loman, from Natal, and four others described by Loman from the East Indies, are the other authenticated species. Of P. philippinense, Semper, I know only the bare record; and P. australe, Grube, is de- scribed only from a larval form with three pairs of legs. P. orientale, Dana (first described as Astridiwm, n.g.), 1s also described from an immature specimen, and more resembles a Phoxichilus. The British Pycnogons. Dr. George Johnston,’ the naturalist-physician of Berwick-on- Tweed, Harry Goodsir,? brother of the great anatomist, who perished with Sir John Franklin, and George Hodge® of Seaham Harbour, a young naturalist of singular promise, dead ere his prime. were in former days the chief students of the British Pycnogons. Of late, Carpenter * has studied the Irish species; and the cruises of the Porcupine, Triton, and Knight Errant have given us a number of deep-water species from the verge of the British area. In compiling the following list, I have had the mdispensable advantage of access to Canon Norman’s collection, and the still greater benefit of his own stores of endless information.’ Pseudopallene circularis, Goodsir : Firth of Forth. Phoxichilidium femoratum, Rathke (P. globosum, Goodsir; Orithyia coccinea, Johnston) (Figs.270, B; 286): East and West coasts, Shetland, Ireland. Anoplodactylus virescens, Hodge (? Phoxichilidium | olivaceum, Gosse) : South coast. 1 Mag. Nat. Hist. vi., 1838, p. 42; Mag. Zool. and Bot. i:, 1837, p. 368. 2 Edinb. New Phil. Journ. xxxii., 1842, p. 136 ; xxxiii., 1842, p. 867 ; Ann. Mag. Nat. Hist. (1), xiv., 1844, p. 4. 3 Ann. Mag. Nat. Hist. (3), xiii., 1864, p. 113. * Proc. R. Dublin Soc. (N.S.), viii., 1893, p. 195; Fisheries, Ireland, Sci. Invest. 1904, No. iv. (1905). ° Cf. A. M. Norman, J. Linn. Soc. xxx., 1908, pp. 198-238. XXI THE BRITISH PYCNOGONS 541 A. petiolatus, Kr. (Figs. 270, c; 275, B; 287) (Pallene attenuata and pygmaea, Hodge ; Phoxichilidium exiguum and longicolle, Dohrn) : Plymouth, Firth of Forth, Cumbrae, Irish coasts. Ammothea (Achelia) echinata, Hodge (Fig. 265, B; 274, 4; 275, 8): Plymouth, Channel Islands, Isle of Man, Cumbrae, Durham (Hodge), West of Ireland. We have not found it on the East of Scotland. A. brevipes, Hodge, is presumed to be the young. Two of Dohrn’s Neapolitan species, A, fibulifera and A. franeiscana, are in my opinion not to be distinguished from one another, nor from the present species. A. hispida, Hodge (Fig. 266, c) (A. longipes, Hodge (juv) ; A. magnirostris, Dohrn ; ? Pasithoe vesiculosa, Goodsir ; ? Pephredo hirsuta, Goodsir): Corn- wall and Devon (Hodge and Norman), Jersey. The form common on the East of Scotland would seem to be this species. The Mediterranean A. magnirostris, Dohrn, appears to be identical. A. laevis, Hodge: Cornwall (Hodge), Devon (Norman), Jersey (Sinel). Tanystylum orbiculare, Wilson (Clotenia conirostre, Dohrn): Donegal (Carpenter), Phoxichilus spinosus, Mont. (Fig. 265, c; 270, a; 275, c): South Coast, Moray Firth, Firth of Clyde, Ireland. A smaller and Jess spiny form occurs which Carpenter records as P. laevis, Grube, but Norman unites the two under the name of Hndeis spinosus (Mont.). Pycnogonum littorale, Strom (Fig. 262): on all coasts, and to considerable depths (150 fathoms, West of Ireland), Nymphon brevirostre, Hodge (N. gracile, Sars) (Figs. 263, 264, 267, a; 272, 274, 3): common on the East Coast ; Herm (Hodge), Dublin, Queens- town (Carpenter). Our smallest species of Nymphon. N. rubrum, Hodge (N. gracile, Johnston; N.. rubrum, G. O. Sars): common on the East Coast ; Oban (Norman), Ireland (Carpenter). N. grossipes, O. Fabr., Johnston (N. johnstoni, Goodsir): Northumber- land, East of Scotland, Orkney, etc., not uncommon. N. gracile, Leach (N. gallicum, Hoek; p N. femoratum, Leach): South of England, West of Scotland, and Ireland. N. strémit, Kr. (N. gigantewm, Goodsir) (Figs. 273, 274, 2): East Coast, from Holy Island to Shetland. Chaetonymphon hirtum, Fabr. (Fig. 274, 1): Northumberland (Hodge), Margate (Hoek), East of Scotland, and Ireland, not uncommon. There seems to be no doubt that British specimens agree with this species as figured and identified by Sars. N. spinoswm, Goodsir (East of Scotland, Goodsir ; Belfast, W. Thompson), is, according to Norman, the same species. Sars’ Norwegian specimens figured under the latter name are not identical, and have been renamed by Norman C. spinosissimum, but are said by Meinert and Mobius to be identical with C. hirtipes, Bell. Hodge (1864) records Nymphon mixtum, Kr., and N. longitarse, Kr., from the Durham coast. His full list of the recorded species of other authors also includes the following doubtful or unrecognised species: N. pellucidum, N. simile, and N. minutwm, all of Goodsir, Pallene brevirostris, Johnston (P. empusa, Wilson ; ? P. emaciata, Dohrn) (Figs. 275, A; 285): all coasts. Examples differ considerably in size and proportions, as do Dohrn’s Neapolitan species one from another. We have specimens from the Sound of Mull that come very near, and perhaps agree 542 PYCNOGONIDA CHAP. XXI with, Sars’ P. producta, a species that scarcely differs from P. brevirostris, save in its greater attenuation ; the same species has also been recorded from Millport and from Port Erin. P. spectrum, Dohrn: Plymouth (A. H. Norman). Besides the above, all of which are littoral or more or less shallow-water species, we have another series of forms, or, to speak more correctly, we have two other series of forms, from the deep Atlantic waters within the British area. In the cold area of the Faeroe Channel we have Boreonymphon robustum, Bell; Nymphon elegans, Hansen; N. sluiteri, Hoek; N. stenocheir, Norman; Colossendeis proboscidea, Sabine; C. angusta, Sars. In the warm waters south and west of the Wyville-Thomson ridge we have Chaetonymphon spinosissimum, Norman; Nymphon gracilipes, Heller (non Fabr.); NV. hirtipes, Bell; N. longitarse, Kr.; V. macrum, Wilson; Pallenopsis tritonis, Hoek (= P. holti, Carpenter) ; “Anoplodactylus oculatus, Carpenter, and A. typhlops, G. O. Sars; and to the list under this section Canon Norman has lately made the very interesting addition of Paranymphon spinosum, Caullery, from the Porcupine Station XVIL., 8.S.E. of Rockall, in 1230 fathoms. Lastly, and less clearly related to temperature, we have Chaetonymphon tenellum, Sars; N. gracilipes, Fabr. ; WV. leptocheles, Sars; WN. macronyx, Sars; N. serratum, Sars ; and Cordylochele malleolata, Sars. Of the species recorded in the above list as a whole, Anoplo- dactylus virescens, Nymphon gracile, and Pallene spectrum reach their northern limit in the southern parts of our own area; Ammothea echinata, Anoplodactylus petiolatus, Pallene brevirostris, and Phoxichilus spinosus (or very closely related forms) range from the Mediterranean to Norway, the last three also to the other side of the Atlantic; Nymphon brevirostre and N. rubrum range from Britain, where they are in the main East Coast species, to Norway. Of the Atlantic species, other than the Arctic ones, the majority are known to extend to the New England coast. INDEX Every reference is to the page: words in italics are names of genera or species ; figures in italics indicate that the reference relates to systematic position ; figures in thick type refer to an illustration ; f. = and in following page or pages ; n. = note. Abalius, 312 Abdomen, of Malacostraca, 110; of Acan- tholithus, 178; of Birgus, 176; of Cenobita, 176 ; of Dermaturus, 178 ; of Hapalogaster, 178; of Lithodes, 178 ; of Pylopagurus, 178 ; of Trilobites, 235 ; of Scorpions, 297 ; of Pedipalpi, 309 ; of Spiders, 317 ; of Palpigradi, 422 ; of Solifugae, 426 ; of Pseudoscorpions, 431 ; of Podogona, 440 ; of Phalangidea, 440, 443 ; of Acarina, 457 ; of Pentastomida, 489 ; of Pyenogonida, 502 Abdominal glands, of Chernetidea, 432 Abyssal region (marine), 204 ; (lacustrine), 209 Acantheis, 418 Acanthephyra, 163 Acanthephyridae, 763 Acanthoctenus, 415 Acanthodon, 388 Acanthogammarus, 138 Acantholeberis, 53 Acantholithus, 181 ; A. hystrix, 178 Acanthophrynus, 313 Acari, 454 (= Acarina, q.v.) Acaridea, 454 (= Acarina, q.v.) Acarina, 258, 454 f.; parasitic, 455; ex- ternal structure, 457 ; spinning organs, 457; internal structure, 459; meta- morphosis, 462 ; classification, 464 Acaste, 249 Accola, 390 Acerocare, 247 Achelata, 429 Achelia, 534; A. longipes, 506 Achtheres, 75; A. percarum, 75 Acidaspidae, 251 Acidaspis, 226, 227, 230, 231, 235, 241, 251; A. dufrenoyi, 250; A. tubercu- lata, larva, 240; A. verneuili, 231; A. vesiculosa, 231 Aciniform glands, 335, 349 Acoloides saitidis, 367 Acroperus, 53; A. leucocephalus, 52 Acrosoma, 410 Acrothoracica, 92 Actaea, 191 ; habitat, 198 Actinopodinae, 387 Actinopus, 387 Aculeus, of scorpion, 303 Admetus, 313 Aegidae, 126 Aegisthus, 61 Aeglea laevis, 169 ; Aegleidae, 169 Aeglina, 227, 249; Ae. prisca, 248 Agelena, 416; A. brunnea, 367 ; A. laby- rinthica, 352, 353, 378, 380, 381, 416 ; A. naevia, 339 Agelenidae, 325, 352, 353, 415 Ageleninae, 4/6 Ageregate glands, 335, 349 Aglaspis, 279 Agnathaner, 66 Agnathonia, 529 Agnostidae, 244 Agnostini, 243 Agmnostus, 222, 223, 225, 231, 234, 245 ; A. integer, 245 Agraulos, 247 Agroeca, 3897 ; A. brunnea, cocoon, 358 Albunea, 171 ; respiration, 170 ; distribu- tion, 201 Albuneidae, 177 Alcippe, 92; A. lampas, 92, 93 Aleock, on Oxyrhyncha, 192; on phos- phorescence, 151 Alepas, S9 Alima, larva of Squilla, 145 Alimentary canal, of Crustacea, 14; of Phyllopoda, 28; of Cladocera, 42; of Squilla, 142 ; of Malacostraca, 110 ; of distribution, 212 543 544 INDEX Trilobites, 222; of Arachnida, 256 ; of Limulus, 268; of Scorpions, 304 ; of Pedipalpi, 310; of Spiders, 329; of Solifugae, 427; of Pseudoscorpions, 434 ; of Phalangidea, 444 ; of Acarina, 459 ; of Tardigrada, 480; of Pentastomida, ’ 491 ; of Pyenogons, 513 Alitropus (Aegidae), habitat, 211 Allman, on larvae of Pycnogons, 523 Alloptes, 466 Alona (including Leydigia, Alona, Harpo- rhynchus, Graptoleberis), 53 Alonopsis, 53 Alpheidae, 163 ; habitat, 198 Alpheus, 163; reversal of regeneration, 156 Alveolus, of palpal organ of Spiders, 322 Amaurobius, 399 ; A, fenestralis, 399; A. ferox, 399 ; A. similis, 399 ; spinnerets, 326 Amblyocarenum, 388 Amblyomma, 470 ; A. hebraeum, 456, 470 Amblypygi, 312 Ammothea, 505, 534; A. achelioides, 534 ; A. brevipes, 541; A. echinata, 505, 509, 510, 534, 541, 542; A. fibulifera, 522, 534, 541; A. franciscana, 541; A. grandis, 534; A. hispida, 534, 535, 541; A. laevis, 541; A. longicollis, 533: A. longipes, 506, 534, 541; A. magnirostris, 534, 541; ) Lamproglena, 68 Lampropidae, 727 Lamprops, 121 Langouste, 165 Laniatores, 448 Lankester, on Crustacean limb, 9; classification of Arachnids, 258, 277 ; on Limulus, 274, 305 Laophonte littorale, 62 ; L. mohammed, 62 Laseola, 404 Lathonura, 53 Latona, 51 Latreille, 385, 408 n., 412, 504, 526 Latreillia, 185 ; distribution, 205 Latreillopsis, 185 ; L. petterdi, 185 Latreutes ensiferus, habitat, 202 Latrodectus, 362, 403; L. 13-quttatus, 364, 403; ZL. mactans, 362, 363, 403 ; L. scelio, 403 Laura, 93; L. gerardiae, 93 Laurie, 309 n., 310, 311 Leach, 526 Lecythorhynchus armatus, 535 Leeuwenhoek, on desiccation in grada, 484 Leionymphon, 534 Lendenfteld, von, 512, 523 Lepas, 87 ; metamorphosis, 80; anatomy, 82; ZL. australis, Cypris, 82; L. fasci- cularis, Nauplius, 81; L. pectinata, pupa, 82 Lephthyphantes, 327, 406 Bempdurus, 23, 24, 36; heart, 29; L. glacialis, range, 34; L. patagonicus, 36; L. productus, 36; carapace, 20; telson, 23; ZL. viridis, 36 Leptestheria, 36; L. siliqua, 37 Leptochela, 163 Leptochelia, 122; L. dubia, dimorphism, 123 Leptoctenus, 418 Leptodora, 54; appendages, 42; alimentary eanal, 43; ovary, ‘44, 45; L. hyalina, 54 Leptodoridae, 54 Leptoneta, 393 Leptonetidae, 393 Leptopelma, 389 Leptoplastus, 247 Leptostraca, 7/7, 242: mentation, 7 Lernaea, 74; L. branchialis, 74, 75 Lernaeascus, 73 Lernaeidae, 74 Lernaeodiscus, 95 Lernaeopoda salmonea, 76 Lernaeopodidae, 75 Lernanthropus, 68 ; blood, 30, 68 Lernentoma cornuta, 72 Leuckart, on Pentastomida, 490, 492; on development of, 494 ; on sub-genera of, 495 Tardi- defined, 6; seg- to) Leuckartia flavicornis, 59 Leucon, 121 Leuconidae, 727 Leucosia, 188 Leucosiidae, 288 ; respiration, 187; habitat, 199 Leydigia, 53 Lhwyd, Edward, on Trilobites, 221 Lichadidae, 252 Lichas, 222, 252 Lichomolgidae, 70 Lichomolgus, 71; L. agilis, 71; L. albeus, 71 Ligia oceanica, 128 Ligidium, 129 Lilljeborg, on Cladocera, 51 n. Limnadia, 21, 22, 36; L. lenticularis, 22, 36 Limnadiidae, 20, 23, 28, 29, 36 Limnetis, 20, 21, 22,56; L. brachyura, 21, 24, 36 Limnocharinae, 47.2 Limnocharis aquaticus, 472 Limulus, 256, 292; nervous system, 257 ; classification, 260, 276 ; segmentation, 260, 261, 262, 266, 270, 272; append- ages, 263 ; habits, 265, 271 ; food, 267 ; digestive system, 268; circulatory system, 268 ; respiratory system, 269 ; excretory system, 270 ; nervous system, 270, 272; eges and larvae, 274, 275; ecdysis, 274; used as food, 275-6 ; affinities, 277; fossil, 277; ZL. gigas, 276; L. hoevent, 277; L. longispina, 264, 274; ZL. moluccanus, 264, 274, 276, 277; L. polyphemus, 261, 262, 264, 271; L. rotundicauda, 275, 277 ; L. tridentatus, 276 Lindstrom, on facial suture of Agnostus and Olenelius, 225; on eyes of Trilo- bites, 228 f.; on blind Trilobites, 231 f. ; on maculae of Trilobites, 255 Lingua, 459 Linguatula, 488 n., 495 ; L. pusilla, 496 ; L. recurvata, 496 ; £. subtriquetra, 496: L. taenioides, 489, 492, 493, 494, 496 ; frequency of, 489 ; larvae of, 489, 494 ; hosts of, 496 Linnaeus, 408 n., 502 Linyphia, 406; L. clathrata, 406; L. marginata, 406; L. montana, 406; L. triangularis, 406 Linyphiinae, 405 Liobunum, 447, 450 Liocraninae, 397 Liocranum, 397 Liphistiidae, 3S6 Liphistioidae, 383 Liphistius, 317, 383, 385, 386; L. de- sultor, 386 Liriopsidae, 730 Lispognathus thompsoni, eyes, 149 556 INDEX Lister, M., 341, 342 Lithodes, 181; L. maia, 176, 177, 178 Lithodidae, 787 ; evolution of, 176 f. Lithodinae, 787 ; distribution, 199, 201 Lithoglyptes, 92; L. varians, 93 Lithotrya, 87 ; L. dorsalis, 87 Lithyphantes, 404 Littoral region, of sea, 197 ; of lakes, 206 Liver (gastric glands), of Crustacea, 14 ; of Branchiopods, 29; of Limulus, 268 ; of Arachnids, 304 f., 331 Lobster, distribution, 199; Mysis sfage, 153; natural history, 154 f. Lockwood, on habits of Limulus, 265, 271 Loeb, 525 n. Loman, 331, 514, 525 Lonnberg, 425 Lophocarenum insanum, 405 Lophogaster, 119 Lophogastridae, 1138, 114, 779 Loricata, 165 Lounsbury, 456, 461 Love dances, among spiders, 381 Lovén, on Trilobites, 226 Loxosceles, 393 Lubbock, 375 Lucas, 364 Lucifer, 162 Lung-books, 297, 308, 336 ; origin of, 305 Lupa, 191; L. hastata, 191 ; resemblance to Matuta, 187, 189 Lycosa, 417 ; L. arenicola, 357; L. caro- linensis, turret of, 357 ; L. fabrilis, 417 ; L. ingens, 418; L. narbonensis, 361, Biss JA Mae Big SUA Cale Vbe tigrina, 357, 369 Lycosidae, 359, 375, 381, 417 Lydella, 479, 485; L. dujardini, 477, 486 Lynceidae, 53; alimentary canal, 43; winter-eggs, 48 ; reproduction, 49 Lyncodaphniidae, 53 Lyonnet, 319, 320 Lyra, 328 Lyriform organs, 3825, 422 Lysianassa, 137 Lysianassidae, 737 Lysianax punctatus, hermit-crab, 172 commensal with M‘Cook, 334, 339, 340, 346, 350, 352 n., 365 n., 366, 367 n., 369 n. M‘Coy, F., on facial suture of Trinwcleus, 226 ; on free cheek of Trilobites, 227 M‘Leod, 336 n. Macrobiotus, 480, 485; M. ambiguus, 487; M. angusti, 486; M. annulatus, 486; M. coronifer, 487; M. crenulatus, 487; M. dispar, 487 ; M. dubius, 487 ; M. echinogenitus, 487; M. harms- worthi, 487; M. hastatus, 487; MM. hufelandi, 480, 482, 483, 486; J. intermedius, 486; M. islandicus, 487 ; M. macronyx, 477, 483, 487; MM. oberhiiusert, 486; M. orcadensis, 487 ; M. ornatus, 487; M. papillifer, 487 ; M. puilari, 487 ; M. sattleri, 487; M. schultzei, 480; M. tetradactylus, 478 ; M. tuberculatus, 487; M. zetlandicus, 486 Macrocheira kiéimpferi, 192 Macrohectopus (= Constantia), 138, 212 Macrophthalmus, 196 Macrothele, 390 Macrothriz, 37, 53 Macrura, 153 f. Macula, 233 Maia, 193; distribution, 205; mM squinado, 192 ; alimentary canal, 15 Maiidae, 793 Malacostraca, 710 f. ; defined, 6; classi- fication, 113, 114 ; fresh-water, 210 f. Malaquin, on Monstrilla, 63 un. Male Spider, devoured by female, 380 Malmignatte, 364, 403 Malpighian tubes or tubules, 12, 257, 311, 331, 427, 434, 460 Mandibles, of Crustacea, 8 ; of Arachnida, 319 Mange, 465 Maracaudus, 449 Margaropus, 469 Marine Spiders, 415 Marpissa, 421; M, muscosa, 420; M. pomatia, 421 Martins, Fr., 502 Marx, 350 Masteria, 390 Mastigoproctus, 312 Mastobunus, 449 Matthew, G. F., on development of Trilo- bites, 238 Matuta, 188 ; habitat, 198 ; MW. banksii, 187 Maxilla, 8 ; of Decapoda, 152 ; of Spiders, 321 Maxillary gland, 13 Maxillipede, 8; of Copepoda, 55, 78 ; of Malacostraca, 113; of Zoaea, 180, 181, 182 Mecicobothrium, 391 Mecostethi, 443, 447, 448 Mecysmauchenius segmentatus, 41 Meek, 3638 Megabunus, 450, 451 Megacorminae, 308 Megacormus granosus, 308 Megalaspis, 222, 249 Megalopa, compared to Glaucothoe, 180 ; of Corystes cassivelaunus, 183 Mégnin, 455, 457 Megninia, 466 Meinert, 522 n. | Meisenheimer, 511 n. INDEX sar Melanophora, 397 Mena-vodi, 362 Menge, 319, 368, 385 Menneus, 410 Mermerus, 449 Merostomata, 258, 259 f. Mertens, Hugo, 524 n. Mesochra lilljeborgi, 62 Mesonacis, 2473; M. asaphoides, larva, 240 Mesosoma, of Arachnida, 256 ; of Limulus, 260, 263; of Hurypterus, 288; of Scorpion, 302 Mesothelae, 386 Meta segmentata, 408 Metamorphosis, of Cirripedia, 80; of Sacculina, 97 ; of Epicarida, 130, 133, 135 ; of Sqguilla, 142, 143; of Huphausia, 144; discovery of, in Decapoda, 153 ; of Lobster, 156; of Crayfish, 157; of Penews, 159 ; primitive nature of, in Macrura, 161; of Loricata, 165, 166; of Hermit-crab, 179; of Brachyura, 181, 182; of Dromiacea, 182; of Trilo- nites; Zoo, of Limulus, 27553 of Pseudoseorpions, 435; of Acarina, 462; of Pentastomida, 493 f.; of Pyenogons, 521 f. Metasoma, of Arachnida, 256 ; of Limulus, 260, 263, of Hurypterus, 289; of Scorpion, 303 Metastigmata, 467 Metastoma, of Trilobites, 234 ; of Euryp- terida, 287, 292 Metazoaea, 182 Metopobractus rayi, 405 Metopoctea, 452 Metridia, 59; M. lucens, distribution, 203 Metronaxz, 398 Metschnikotf, 435 n. Miagrammopes, 411 Miagrammopinae, 4/7 Micaria, 397; M. pulicaria, 396, 397 ; M, scintillans, 372 Micariinae, 397 Micariosoma, 397 Michael, 460, 461, 462, 466 n. Micrathena, 410 Microdiscus, 225, 231, 245 Microlyda, 486 n. Micrommata, 414; M. 414 Microneta, 406 Microniscidae, 730 Migas, 387 Miginae, 387 Milne-Edwards, 504 Milnesium, 480, 485 ; M. alpigenum, 487 ; M. tardigradum, 487 Miltia, 396 Mimetidae, 477 Mimetus, 411; M. interfector, 368 virescens, 413, Mimicry, in Spiders, 372 Mimoscorpius, 312 Miopsalis, 448 Misumena, 412; M. vatia, 371, 373, 412 Mites, = Acarina, q.v. Moggridge, 354, 355 n. Moggridgea, 3S7 Moina, 37, 52; reproduction, 46, 47, 48, 49; M. rectirostris, 46, 47, 52 Mole-crab, 170 Monochetus, 465 Monolistra (Sphaeromidae), habitat, 211 Monopsilus, 54 Monostichous eyes, 301 Monstrilla, 64 Monstrillidae, 63 Morgan, 517, 518, 521 Mortimer, Cromwell, on Trilobites, 221 Mosaic vision, 147 Moseley, 525 Moulting (Eedysis), 154, 155, 225, 338 Mouth, of Trilobites, 234 Mud-mites, 472 Miiller, F., on Tanaids, 123 Miiller, O. F., on position of Tardigrada, 483 Munidopsis, 170; eyes, 149; MW. hanata, 168 Munnopsidae, 728 Munnopsis typica, 127 Murray, 455 Murray, J., on British Tardigrada, 485 Muscular system, in Tardigrada, 481; in Pentastomida, 490 Mygale, 337, 386 n., 389 Mygalidae, = Aviculariidae, q.v. Myrmarachne formicaria, 421 Myrmecium, 397 Myrtale perroti, 587 Mysidacea, 178 Mysidae, 113, 114, 2279; habitat, 201; relation to Webalia, 112 Mysis, 120 ; maxillipede, 10, 11 ; resem- blance to Paranaspides, 117 ; M. oculata, var. relicta, 120, 210; MM. vulgaris, 118 Mysis-larva, of Lobster, 156; of Peneus, 161 Mytilicola, 6S Nanodamon, 313 Nauplius, of Haemocera danae, 64; of Lepas fascicularis, 81; of Sacculina, 97; of Huphausia, 144; an ancestral larval form, 145; of Peneus, 159 ; com- pared with Protaspis, 239 Nebalia, 111, 112, 114 ; segmentation, 6, 7: limbs, 10, 11; relation to Cumacea, 120 ; compared with Trilobita, 242; 4. geoffroyt, 111 Nebo, 307 Neck-furrow, 224 558 Nemastoma, 448, 451; iN. 452; N. lugubre, 452 Nemastomatidae, 457 Nematocarcinus, 163 Nemesia, 388 ; N. congena, 355, 357 Neolimulus, 278, 279 Neoniphargus, distribution, 216 Neopallene, 537 Nephila, 408; N. chrysogaster, 380; N. plumipes, 366 Nephilinae, 408 Nephrops, 154; N. andamanica, distribu- tion, 205; WV. norwegica, 205 Nephropsidae, 754 ; resemblance to Dromi- acea, 184 Neptunus, 191; N. sayi, habitat, 202 Nereicolidae, 73 Nervous system, of Crustacea, 5; of Branchiopoda, 30; of Squilla, 142; of Arachnida, 257 ; of Limulus, 270; of Scorpions, 305; of Pedipalpi, 311; of Spiders, 332, 333; of Solifugae, 428 ; of Pseudoscorpions, 434 ; of Phalangidea, 445, 446; of Acarina, 460; of Tardi- grada, 482; of Pentastomida, 491; of Pyenogons, 516 Neumann, 470 Nicodaminae, 476 Nicodamus, 416 Nicothoe astaci, 6S Nileus, 229, 249; N. armadillo, eye, 228 Niobe, 249 Niphargoides, 138 Niphargus, 137, 138; distribution, 216 ; N. forelii, 138; N. puteanus, habitat, 209, 210 Nogagus, 73 Nops, 315, 336, 395 Norman, A. M., 540 Notaspis, 467 Nothrus, 468 Notodelphys, 66 Notostigmata, 473 Wyctalops, 312 Nycteribia (Diptera), 526 Nymph, 463 Nynphon, 503, 4536; N. brevicaudatum, 507, 536 ; WV. brevicollum, 511, 521; N. brevirostre, 503, 504, 506, 508, 509, 541, 542; W. elegans, 506, 542; WN. Jemoratum, 541; N. gallicum, 541; NV. gracile, 511, 541, 542; N. gracilipes, 542; VV. grossipes, 541; N. hamatum, 512; WN. hirtipes, 542; WN. horridum, 537; NV. johnstoni, 541; N. leptocheles, 042); iV. “longutarse: 54, “542)s) TNE macronys, 542; N. macrum, 542; N. minutum, 541; WN. mixtum, 5413; N. pellucidum, 541; N. rubrum, 541, 542; NV. serratum, 542; WN. simile, 541; NV. sluiteri, 542; N. spinosum, 541; N. stenocheir, 542; N. strémii, 509, 541 chrysomelas, INDEX Nymphonidae, 536 Nymphopsinae, 535 n. Wymphopsis, 534, 585 n. 3 534; iV. muscosus, 534 iV. korotnevi, Obisiinae, 436, 437 Obisium, 436, 438 Ochyrocera, 393 Octomeridae, 97 Octomeris, 91 Ocyale mirabilis, 416 Ocypoda, 194, 196 ; habitat, 198 ; distri- bution, 201 Ocypodidae, 796 Oecobiidae, 386 n., 392 Ocecobius, 392; Oe. maculatus, 392 Oehlert, on facial suture of Zvrinucleus, 226 Ogovia, 448 Ogygia, 249 Oiceobathes, 5385 Oithona, G1; O. nana, 203; O. plumifera, 203 Olenelloides, 247 ; O. armatus, 247 Olenellus, 225, 227, 232, 236, 247 Olenidae, 247 Olenus, 232, 247 ; O. truncatus, 248 Oligolophus, 450; O. agrestis, 450; O. spinosus, 441, 450, 451 Olpium, 436, 457 ; O. pallipes, 437 Ommatoids, 310, 311, 312 Oncaea, 69; O. conifera, phosphorescence, 60 Oneaeidae, 69 Oniscoida, 728 Oniscus, 129 Ononis hispanica, Spiders on, 419 Onychium, 324 Oomerus stigmatophorus, 539 Oonopidae, 336, 593 Oonops, 394; O. pulcher, 366, 394 Oorhynchus, 507, 585; O. aucklandiae, 535 Oostegites, of Malacostraca, 114 Operculata, 89, 91 Ophiocamptus (Moraria), 62; O. brevipes, Opilioacarus, 454, 473; O. arabicus, 473 ; O. italicus, 473; O. platensis, 473; O. segmentatus, 473 Opiliones (= Phalangidea, q.v.), 440 Opisthacanthus, 307 Opisthoparia, 244 Opisthophthalmus. 307 Opisthothelae, 386 Opopaea, 394 Orchestia, 139 ; hermaphroditism, 104 ; O. gammarellus, 137, 139 ; habitat, 211 Orchestina, 394 Orihata, 467 Oribatidae, 457, 458, 459, 460, 462, 467 ; anatomy, 459 INDEX 559 So Orithyia coccinea, 524, 540 Ornithodoros, 469. O. megnini, 469; O. moubata, 469 ; O. talaje, 469; O. turi- cata, 469 Ornithoscatoides, 374 Orometopus, 226, 245 ; O. elatifrons, 230 Ortmann, on Brachyura, 181 n. ; on bipo- larity, 200 ; on crayfishes, 218 ; on Pyc- nogons, 513 n. Ostracoda, 107 ; pelagic, 202 Oudemans, 528 n. Ovary, of Cladocera, 44, 45 ; of Danalia, 132 ; of Spiders, 332 Oxynaspis, 88 Oxyopes, 419 ; O. lineata, 419 Oxyopidae, 479 Oxyptila, 412 Oxyrhyncha, 797 f. ; habits, 192 ; enemies, 192 ; habitat, 198 Oxystomata, 185 f. ; respiration, 186, 187 Pachycheles, 170; P. panamensis, distri- bution, 202 Pachygnatha, 407 ; P. clerckii, 407 ; P. degeerti, 407 ; P. listeri, 407 Pachygrapsus, 196 ; P. marmoratus, 193, 194, 196 Pachylasma giganteum, 91 Pachylomerus, 388 Pachysoma, 69 Paguridae, 780; eyes of deep-sea, 149, 150 Paguridea, 771 Pagurinae, 780 Palaemon, 1643; excretory glands, 13 ; fresh-water, 212 ; P. serratus, 158, 164 ; Bopyrus parasitic on, 133 Palaemonetes, 164; P. antrorum, habitat, 210; P. varians, 161 ; distribution, 212 Palaemonidae, 159, 164 Palaeocaris, 115, 118 Palaeophonus, 294, 298 Palamnaeus, 307; P. tarsus, 304 Palinuridae, 167 Palinurus, 165, 167 ; habitat, 198, 202 ; P. elephas, 167; P. quadricornis, em- bryo, 165 Pallene, 505, 587; P. attenuata, 541; P. brevirustris, 510, 524, 537, 541, 542; P. dimorpha, 538; P. emaciata, 541 ; LZMCHUDUSH OL Le OTULI OSS 3 P: languida, 537; P. longiceps, 588; P. novaezealandiae, 537; P. producta, 542; P. pygmaea, 537, 5413; P. spectrum, 542 ; P. spinosa, 537 Pallenidae, 537 Pallenopsis, 506, 511; P. holti, 542; P. tritonis, 542 Palp, of Pyenogons, 507 Palpal organ, 322, 378 Palpebral lobe, 227 swammerdami, Palpigradi, 258, 422 Palpimanidae, 323, 325, 398 Palpimanus, 398 Panamomops diceros, 405 Pandalidae, 164 Pandalus, 164; P. annulicornis, 164 Pandinus, 307 Panoplax, 195 Pantopoda, 501 n. (=Pycnogonida, ¢.v.) Panulirus, 165, 167 Parabolina, 232, 247 Parabolinella, 247 Parabuthus, 298 ; P. capensis, 298, 299 Paradoxides, 222, 232, 236, 247; P. bohemicus, 246 Paragaleodes, 429 Paralomis, 179, 181 Paranaspides, 117; P. lacustris, 117; distribution, 210; habitat, 210 Paranebalia, 242 Paranephrops, 157 ; distribution, 213 Paranthura, 124 : Parantipathes, Synagoga parasitic on, 94 Paranymphon, 507 ; P. spinosum, 542 Parapagurus, 180 Parapallene, 537 Parapeneus, 162 ; P. rectacutus, 159 Parapylocheles scorpio, eyes, 149 Parasiro, 448 ; P. corsicus, 448 Parasites, in Tardigrada, 484 Parasitic castration, 100, 136 Parastacidae, 757 ; distribution, 213 Parastacus, 157 ; distribution, 213 Paratropidinae, 387 Paratropis scrupea, 387 Parazetes auchenicus, 633 Pardosa, 417; female carrying young, 341; P. amentata, 417, 418 ; P. lugu- bris, 418 Pariboea spinipalpis, 534 Parthenogenesis, in Phyllopoda, 32; in Cladocera, 44, 46, 49 ; in Ostracoda, 108 Parthenope, 193 ; P. investigatoris, 192 Parthenopidae, 193 Pasiphaea, 163 Pasiphaeidae, 163 Pasithoe, 532; P. umbonata, 535; P. vesiculosa, 535, 541 Pasithoidae, 532 Patten, 270, 271, 277 Patten and Redenbaugh, on Limulus, 266, 270, 272 Paturon, 319, 320 Peckham, 376, 377, 378, 381, 382 Pecten, 328 Pectines, of Scorpions, 302, 302 ; function of, 299 ; of Glytoscorpius, 294 Pedicle, 317 Pedipalpi, 258, 308 ; habits, 309 ; external structure, 309; legs, 309; internal structure, 310; alimentary canal, 310; nervous system, 311 ; classification, 312 560 Pedipalpi (appendages), 263, 303, 309, 821, 422, 426, 433, 440, 458 Pedunculata, 84 Pelagic Crustacea, marine, 202 ; trine, 207 Pelops, 467 Peltiidae, 63 Peltogaster, 95 ; structure, 95; males, 99; castration caused by, 100; P. curvatus, castration caused by, 100; P. sulcatus, 95 Peltura, 247 Peneidae, 762 Peneidea, 758, 162; metamorphosis, 159 Penella sagitta, 74 Peneus, 158, 162; metamorphosis, 159, 159, 160, 161 Pentanymphon, 504, 537 Pentaspidae, 87 Pentastoma, 488 n.; P. denticulatum, 489, 494; P. emarginatum, 489; P. serratum, 489 Pentastomida, 258, 488 f.; structure, 489; habitat, 488; life-history, 488, 493 ; hosts of, 496, 497 Pephredo hirsuta, 535, 541 Peracantha, 43, 53; alimentary canal, 43 Peracarida, 114, 77S Pereiopod, defined, 110; reduced hind, in Galatheidea, 168; in Hippidea, 170; in Paguridea, 172 ; in Dromiacea, 184 ; in Oxystomata, 185 Periegops hirsutus, 393 Peroderma cylindricum, 75 Petrarca bathyactidis, 93 Pettalus, 448 Pezomachus gracilis, parasitic in cocoons of Spiders, 367 Phacopidae, 249 Phacopini, 243 Phacops, 223, 232, 235, 249 ; P. latifrons, 227; P. sternbergi, 248 Phaeocedus braccatus, 397 Phagocytes, in Danalia, 132 Phalangidea, 258, 440 f.; habits, 441 ; ex- ternal structure, 442 ; internal structure, 444; nervous system, 446; classifica- tion, 447 ; British species, 453 Phalangiidae, 449 Phalangiinae, 450 Phalangium, 444, 450, 526 ; mouth-parts, 443; P.balaenarum, 502 ; P. cornutum, 450; P. littorale, 501; P. opilio, 445, 446, 450, 526 Phalangodes, 449 ; terricola, 449 Phalangodidae, 448 Phanodemus, 535 Phidippus, 421; P. morsitans, 3865, 421 Philichthyidae, 73 Philichthys, 73; P. xiphiae, 73 n. Phillipsia, 251; P. gemmulifera, 250 Philodrominae, 473 lacus- P. armata, 449; P. INDEX Philodromus, 413; P. aureolus, 413; P. margaritatus, 413 Philoscia muscorum, 129 Pholcidae, 336, 407 Pholcus, 320, 401; P. 401 Phoroncidia, 404; P. 7-aculeata, 318 Phoroncidiinae, 317, 404 Phosphorescence, of Copepoda, 59; rela- tion to eyes in deep-sea Crustacea, 150, 151 Phosphorescent organs, of Euphausiidae, 145; of Stylochetron mastigophorum, 151 Phoxichilidae, 539 Phoxichilidiidae, 538 Phoxichilidium, 506, 512, 520, 521 n., 523, 525,538 ; P. angulatwm, 520; P. exiguum, 541; P. femoratum, 508, 524, 538, 540; P. globosum, 540; P. mollis- simum, 517; P. olivacewm, 540 Phoxichilus, 505, 512, 539; P. australis, 539, 540; P. bohmii, 589; P. charyb- daeus, 514, 515, 589; P. laevis, 537, 539, 541; P. meridionalis, 5389; P. mollis, 589; P. proboscideus, 532; P. procerus, 539; P. spinosus, 505, 508, 510, 537, 539, 541, 542; P. vulgaris, 539 Phreatoicidae, 217 Phreatoicidea, 736 Phreatoicopsis, 136 ; distribution, 211 Phreatoicus, 136 ; distribution, 210, 211, 217; P. assimilis, habitat, 210; P. typicus, habitat, 210 Phronima, 140; P. sedentaria, 140 Phrynarachne, 414; P. decipiens, 374, 414 Phrynichinae, 373 Phrynichus, 313 Phrynidae, 309, 310, 312 Phrynopsis, 313 Phrynus, 312 Phryxidae, 730 Phyllocarida, 777, 242 Phyllocoptes, 465 Phyllopoda, 79 f.; appendages, 24 f. ; alimentary canal, 29; vascular system, 29; nervous system, 30; reproductive organs, 31; habitat, 32; genera, 35 Phyllosoma, larva of Palinurus, 166 Phytoptidae, 464 Phytoptus, 464 n., 495 (= Hriophyes, q.v.) Pickard-Cambridge, F., 352 Pickard-Cambridge, O., 318, 321 n., 323 n., 359 n., 372, 374, 380, 385, 401 n., 436, 438, 450, 451, 452 Pillai, 375 Pilumnus, 191 Pinnotheres pisum, 195 Pinnotheridae, 795 phalangioides, 136; distribution, 211, INDEX 561 Pipetta, 514, 533; P. weberi, 533 Pirata, 417 Piriform glands, 335, 349 Pisa, 193 Pisaura mirabilis, 416 Pisauridae, 416 Placoparia, 251 Plagiostethi, 443, 447, 449, 452 Plagula, 317 Planes minutus, habitat, 202 Plankton, characters of, 203 ; fresh-water, 207, 216; Cladocera in, 50 Plastron, 316 Plate, on Tardigrada, 481, 482, 484 * Plator insolens, 415 ° Platoridae, 475 Platyarthrus hoffmannseggii, 129 Platyaspis, 121 Platybunus, 450, 451 Platycheles, 535 Plectreurys, 393 Pleopod, defined, 110 Pleura, 234 f. Pleurocrypta microbranchiata, 133 Pleuromma, 59; P. abdominale, 59; P. gracile, 59 Pliobothrus symmetricus, Pycnogon larvae in, 523 Pocock, 298, 308 n., 312, 328, 329, 425 n., 534 n. Podasconidae, 730 Podogona, 258, 439 Podon, 54 _ Podophthalmata, 112 Podoplea, 67 Podosomata, 501 n. (= Pyenogonida, q.v.) Poecilotheria, 390 Poisonous hairs, of Spiders, 365 Pollicipes, S84; fertilisation, 86 ; P. cornu- copia, 85; P. imitella, 85 Pollock, 340 Poltyinae, 410 Poltys, 410; P. ideae, 318 Polyartemia, 86 ; antennae, 26, 28 ; range of, 34; P. forcipata, 36 Polyaspidae, 54 Polycopidae, 109 Polygonopus, 539 Polyphemidae, 44; appendages, ovary, 47 ; reproduction, 49 Polyphemus, 47, 54; P. pediculus, habi- tat, 206, 208 Polysphincta carbonaria, Spiders, 368 Pompeckj, on Calymenidae, 244 Pompilus, 368 Pontellidae, 60 Pontoporeia, 137; distribution, 212; P. afinis, 1388; P. femorata, 138; P. loyt, 1388; P. microphthalma, 138 Porcellana, 168, 170;° Zoaea, 168; P. platycheles, 170 VOL. IV 42); parasitic on Porcellanidae, 17 Porcellio, 129 Poreupine, 540 Porhomma, 406 Porocephalus, 488 n., 495 ; P. annulatus, 490, 496; P. aonycis, 496; P. armil- latus, 496; P. bifurcatus, 496; P. clavatus, 496 ; P. crocidura, 496; P. crotali, 496; P. geckonis, 496; P. gracilis, 496; BP. heterodontis, 496 ; P. indicus, 496; P. lari, 496; P. megacephalus, 497; P. megastomus, 497 ; BP. moniliformis, 497; P. najae sputatricis, 497 ; P. oxycephalus, 497 ; P. platycephalus, 497 ; P. proboscideus, 493, 494; larvae of, 493, 494; hosts of, 496; P. protelis, larva, 495; P. subuliferus, 497; P. teretiusculus, 489, 491, 492, 492, 497; P. tortus, 497 Portunidae, 797 Portunion, 134; P. maenadis, 134 ; life- history, 135, 136 Portunus, 191 Potamobius (=Astacus), 157 ; distribu- tion, 213 Potamocarcinus, 191 ; distribution, 213 Potamon, 191 Potamonidae, 797 Praniza, larva of Gnathia, 125 Prawn, 151, 153, 158, 164, 198; fresh- water, 212, 214 Pre-epistome, 443 Prestwichia (Euprodps), 275, 278, 279 Preyer, on anabiosis in Tardigrades, 484 Prionurus, 298, 299 ; habitat, 198 | Prismatic eye, of Trilobites, 229 Procurved eyes, 316 Prodidomidae, 395 | Prodidomus, 3896 Proétidae, 257 Prottus, 251; P. bohemicus, 248 Prokoenenia, 423; P. chilensis, 423; P. wheelert, 423 Prolimulus, 279 Promesosternite, in Limulus, 264 Proparia, 244 Prosalpia, 450 Prosoma, of Arachnida, 260 ; of Limulus, 260, 263; of Eurypterida, 285; of Scorpion, 301 Prosthesima, 397 Prostigmata, 477 Protaspis, 239, 239, 240 Proteolepas, 94; P. bivincta, 94 Protocaris, 243 Protolenus, 247 Protolimulus, 279 Protolycosa anthrocophila, 383 Przibram, on regeneration in Crustacea, 156 Psalidopodidae, 764 ; habitat, 204 Psalidopus, 164 20 562 INDEX Psalistops, 389 Psechridae, 399 Psechrus, 899 Pseudalibrotus, 137 Pseudidiops, 388 Pseudocuma, 121; distribution, 215 Pseudocumidae, 72/ Pseudoniscus, 279 Pseudopallene, 511, 437; P. 540; P. spinipes, 537 n. Pseudoscorpiones, 258, 430 f.; habits, 430; external structure, 431, 432 ; internal structure, 433 ; development, 434, 435; classification, 436 ; British species, 438 Pseudo-stigmatie organs, 467 Pseudozoaea, larva of Stomatopod, 143 Pterocuma, 121 Pterolichus, 466 Pteronyssus, 466 Pterygometopus, 249 Pterygotus, 283, 291, 292; P. osiliensis, 290 Ptychoparia, 247 Pucetia viridis, 419 Pupa, of Cirripedia, 81, 82 Purcellia, 448 Pychnogonides, 501 n. Pyenogonida, 507 f. ; body, 505 ; chelo- phores, 505; palpi, 507; ovigerous legs, 507 ;. glands, 511; alimentary system, 513; circulatory system, 516 ; nervous system, 516; eyes, 5173 in- tegument, 518; reproductive organs, 519; eggs, 520; development, 520; habits, 524 ; systematic position, 525 ; classification, 528 f.; British species, 540 f. Pycnogonidae, 539 Pycnogonum, 503, 539; P. australe, 540; P. crassirostre, 540; P. Jlittorale, 501, 540, 541; P. magellanicum, 540; P. magnirostre, 540; P. microps, 540; P. nodulosum, 540 ; P. orientale, 540; P. philippinense, 540; P. pusillum, 540 ; P. stearnsi, 540 Pygidium, 235 Pylocheles, 180; P. miersti, 173 Pylochelidae, 780 ; habitat, 204 Pylopagurus, 180 ; relation to Lithodidae, Wiis Las Pyrgoma, 92 circularis, Rachias, 388 Railliet, on classification of Pentastomids, 495 Ranina dentata, 188 Raninidae, 788 Rastellus, 320, 387 Ratania, 68 ; mouth, 63 Réaumur, 360 Recurved eyes, 316 Red spider, 455, 472 Red-water, 456 Regeneration, of Crustacean limbs, 155, 156 Regillus, 414 Reichenbach, on embryology of (eal. oy Aba aa 19) Ly, ie a Ae Nal ‘| vel Ws tae es ‘5 re ata a eo aa ut eeu ar i : aa oR ¥ Wy) Ses 54 Pe Ta Ye F. wha ha a bis oie Aedes Ee = ai | \s WA toe ie wnat ae } | et Tr \ Me - a eur) oom is 4 ' ne Fj 4 ‘ 1fhes aI hie. 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