md Mow ey 2 Nato MT Reta i q mm 2 SBA os Pe ar i an rae Paria a > Tanne ann hy ler eadaiber ss we - : CST eee aenen - ; Se fog Seren rs etumttuaneat gt a shedine Ge ay eh they Sth NO el oe arate Me * Rome ve stmt Hh bohm pa ¥ ca ee ee " " "J . ¥ thank ipa seh eked’ rec ax 1 Spotty! ” ea Seas “ i notin Ms Man Be Me Ma Nth bien oes Seri Dai. Bi Var test at ‘ 5 ach ode . M ~ acta : extoy SANA PL chaaroel anes _ a . eat M sAbont tte att ath eat Beloit heh ak ay . AN AND oh Sorat ts 03? i Mano Mn Ta Yay, rit hp che saving 7 sa Be nah oh s eCity MA ets OE let lt aw kd eos eno pean dats yo tides an tol oct A eH Ml nthe then. fe asada ee Sheth iin “ faded en athe Tenth ST memes ton dy 4 Mhateafor ae ae Date tan IRE REEDS me TR I tn Ot went erm i Sots >, > Sen Sn Fin PRSHER Yess Pastia rons ' ‘ a Cae arora ths Me te este nN A ey 9 At ee kate RD Mae Maa te hn . ‘ q sn * ° “4 nen" Yi ietha om Nt het 5 : * ee a % Ae eee ee = ure me en W593 te © Ln ee Year 0, / ait | + 1? y Ls a ve = i " \ a : 7 ia fa Pie j 7 cut an MW a) af 7 i - - j > i ey eee: a. es ; THE CAMBRIDGE NATURAL HISTORY EDITED BY 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 A. BE. SHIPLEY, M.A., Fellow and Tutor of Christ’s College, Cambridge ; Reader in Zoology in the University VOLUME IV 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 mRUSTACEA By GEorrrey Smitu, M.A. (Oxon.), Fellow of New College, Oxford ; and the late W. F. R. WeE.Lpon, M.A. (D.Sc.,Oxon.), formerly Fellow of St. John’s College, Cambridge, and Linacre Professor of Human and Comparative Anatomy, Oxford WRILOBITES By Henry Woops, M.A., St. John’s College, Cambridge ; University Lecturer in Palaeozoology INTRODUCTION TO ARACHNIDA, AND KING-CRABS By A. E. Surpiey, 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 Pe ORPIONS, SPIDERS, MITES, TICKS, Ere. By Ceci, Warpurton, M.A., Christ’s College, Cambridge ; Zoologist to the Royal Agricultural Society TARDIGRADA (WATER-BEARS) By A. E. Surprey, M.A., F.R.S., Fellow and Tutor of Christ’s College, Cambridge ; Reader in Zoology PENTASTOMIDA By A. E. Surptey, 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 MACMILLAN AND CO, LIMITED Sieh LIN'S STREED, LONDON 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. CHARLES 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. SoutHey, 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 THE Editors feel that they owe an apology and some explanation to the readers of 7he Cambridge Natural History for the delay which has occurred 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 $ @ CONTENTS PAGE SCHEME OF THE CLASSIFICATION ADOPTED IN THIS VOLUME . 3 ‘ : xi CRUSTACEA CHEPAE TUR RVeL CRUSTACEA GENERAL ORGANISATION i : : ‘ 5 ; x . : s 3 OWSLAIP ANTS aey JUL CRUSTACEA (continued) ENTOMOSTRACA —- BRANCHIOPODA — PHYLLOPODA — CLADOCERA — WATER- KEEAS!) 7 : : 4 : ‘ F Fi : P : : 18 (OUeLAVIPMDID IR, UO CRUSTACEA ENTOMOSTRACA (continued) CoPpEPODA : é : : : ; : ; : E ; é } 55 CHAE MAIR Vi CRUSTACEA ENTOMOSTRACA (continued) CIRRIPEDIA—PHENOMENA OF GROWTH AND SEX—OsTRACODA ; ; : 79 vil Vill CONTENTS CHAPTER V CRUSTACEA (continued) PAGE MaALaAcostraca: LEPTOSTRACA—PHYLLOCARIDA: EUMALACOSTRACA: SYN- CARIDA — ANASPIDACEA:. PERACARIDA — MysmpACcEA — CUMACEA — IsopopDA—AMPHIPODA : HOPLOCARIDA—STOMATOPODA . é : ee) CHEAGEIMNimaaval CRUSTACEA MALACOSTRACA (continued) EUMALACOSTRACA (CONTINUED): EUCARIDA — EUPHAUSIACEA — CoMPOUND EvEs—DECAPODA . ‘ : : : : : ‘ ; i oi iets! @H EAR ER Viel CRUSTACEA (continued) REMARKS ON THE DISTRIBUTION OF MARINE AND FRESH-WATER CRUSTACEA. 197 CHAPTER VIII CRUSTACEA (continued) TRILOBITA . ; : : A : - ; : s ? P ee ARACHNIDA CHAP TE Re 1X ARACHNIDA—INTRODUCTION . A ; ; : : , 4 ; , | 255 CHAPTER X ARACHNIDA (continued) bo On =) DELOBRANCHIATA = MEROSTOMATA—XIPHOSURA . : : ; CHAPTER XI ARACHNIDA DELOBRANCHIATA (continued) EuURYPTERIDA=GIGANTOSTRACA . : : é ; 5 ‘ F of pes CONTENTS 1X CHAPTER XII ARACHNIDA (continued) PAGE EMBOLOBRANCHIATA—SCORPIONIDEA—PEDIPALPI . ? : : ; 5. OB (OSL AWeMMD Ie, DOU ARACHNIDA EMBOLOBRANCHIATA (continued) ARANEAE—EXTERNAL STRUCTURE—INTERNAL STRUCTURE . , ; oil CHAPTER XLV: ARACHNIDA EMBOLOBRANCHIATA (continued) ARANEAE (CONTINUED) — HApits — Ecpysis— TREATMENT OF YOUNG — MIGRATION — WrExss — Nests — Eae-cocoons — Poison — FERTILITY — ENEMIES—PROTECTIVE COLORATION—MIMICRY—SENSES— INTELLIGENCE —Matine Hapsirs—FossiL SPipERs : ; F : : , a oo8 CUEAIP MMAR DAV ARACHNIDA EMBOLOBRANCHIATA (continued) ARANEAE (CONTINUED)—CLASSIFICATION : ; : : : ; 5) isk! CHEVACR AINE sexo vil ARACHNIDA EMBOLOBRANCHIATA (continwed) PALPIGRADI—SOLIFUGAE = SOLPUGAE—CHERNETIDEA = PSEUDOSCORPIONES . 422 CHAPTER XVII ARACHNIDA EMBOLOBRANCHIATA (continwed) Popogona = RIcINULEI—PHALANGIDEA = OPILIONES— HABiITs—STRUCTURE— CLASSIFICATION : F ; ‘ : : . 5 : : Sales) (CHELNIPALID IN, SOWANUL ARACHNIDA EMBOLOBRANCHIATA (continued) ACARINA—HARVEst-BUGS— PARASITIC MirEs—-Ticks—SpInningc MitEs— SrrucruRE—METAMORPHOSIS—CLASSIFICATION : ; ; . 454 x CONTENTS CHAPTER XIX ARACHNIDA (APPENDIX 1) PAGE TARDIGRADA — OccURRENCE — Ecpysis — SrrucruRE — DEVELOPMENT — AFFINITIES—BIOLOGY—DESICCATION—PARASITES—SYSTEMATIC . ean (CISPALIEME ID ey, NOS w ARACHNIDA (APPENDIX II) PENTASTOMIDA — OcCURRENCE — Economic IMPORTANCE — STRUCTURE — DEVELOPMENT AND LiFE-HISTORY—SYSTEMATIC . ‘ ; : . 488 PYCNOGONIDA (OUST AIPM MID IR = OCI PYCNOGONIDA : : ; : : : i 3 5 A s SD Ot: INDEX 5 c : : . : ; ; , é : ; . 543 SCHEME OF THE CLASSIFICATION ADOPTED IN THIS VOLUME The names of extinct groups are printed in italics. CRUSTACEA (p. 3). ENTOMOSTRACA (p. 18). Divisions. Orders. Sub-Orders. Tribes. Families. Branchipodidae (pp. 19, 35). Phyllopoda Apodidae (pp. 19, 35) | (pp. 19, 36). Limnadiidae (pp. 20, 36). ee & J Holo os } E diida (82) (p. 51). pea Daphniidae (p. 51). po 18) Calyptomert a Bosminidae (p. 538). Ke (pp. 38, 51) | Anomo- Lyncodaphniidae eae es a (G95 08) (p. 37) (p. 51) Lynceidae = Chydoridae (p. 53). ‘Polyphemidae Gymnomera | | (p. 54). (pp. 388, 54) | Teaches (p. 54) ferns p57) Calanidae (p. 57). Sa Aa tee (p. 58). (p. 57) | Heterarthrandria (p. 58) Gaviandes p- 60) ] 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. 3 Giesbrecht, Mitth. Zool. Stat. Neap. xi., 1895, p. 648. 60 CRUSTACEA——-COPEPODA CHAP. Heterochaeta papuligera, 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 if Fic. 27.—Dorsal view of Anomalo- cera pattersoni, 6, x 20. (After Sars. ) colours, and has nothing to do with 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 Gniesbrecht 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. Fam. 3. Pontellidae—This is a larger family also comprising 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 oreatly from those in the female, being often geniculated and acting as prehensile organs. Fic. 28.—EHuterpe acutifrons, 2, Fie. 29.—First antenna of x 70. > z Nauplius eye; g/, cement-gland ; im, mantle-cavity ; 0, its opening; ov, ovary ; 5 3 > 5 > axe « Pp, penis ; s, seutum ; ¢, testis ; fim, 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. ) G 7 starting with the typi- | { ) ) cal number eight (Fie. 1 'e) Re yy 63, A), we find that ae ey Ms in various degrees a R R R.L+R+R.L fusion between neigh- . . ‘ } " qe m q F -eHlats lato ae anineee taken place in the (Hexameridae); C, Tetraclita (Tetrameridae). C, different families. CN ee ea ; ZL, 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 1s 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 majority 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 B. tintinnabulum of our coasts being found all over the world, and oceurring 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 compheated 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 Fic. 64.—Alcippe lampas. A, 9, 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; ©, 1st pair of cirri; Cr, posterior thoracic appendages ; H, eye; G, testis; M.C, mantle-cavity; O, ovary; P, penis; 7, penultimate thoracic seg- ment; V. vesicula seminalis. (After Darwin.) which live in cavities excavated in the shells of molluscs 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, 1t 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; Kochlorine 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 (Gerardia). 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. 2 Arch. Zool. Exp. viii., 1880, p. 537. OUONE. i. Micr, Sct. 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 prinitive. Other forms are Dendrogaster astericola on Echinoderms, and Synagoga mira on the “ Black Coral,’ Parantipathes lari, at Naples. Sub-Order 5. Apoda. Darwin described a small hermaphrodite parasite in the mantle chamberof Alepas cor- i 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, ee a, 6, Ist and 2nd abdominal segments; 0. ovary ; fixation is effected. ney T, 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. 1 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, Sacewlina 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, eg. 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-lhke portion is very simple, and varies only in details, chiefly of symmetry, in the different genera. In Peltogaster, 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- Fic. 66.—Nearly median longitudinal section (diagram- matic) of Peltogaster. gn, Brain; m, mantle ; mc, cavity (me) or brood- mantle-cavity ; mes, mesentery ; op, mantle-open- : ; ing; ov, ovary; ovd, oviduct ; ring, ring 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. Exp. (2), ii., 1884, p. 417; G- Smith, Pawna wu. 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) les 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 ; v/, 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. carcini 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 A B Fic. 68.—Development of Sacculina neglecta. A, Nauplius stage, x about 70; B, Cypris stage, x about 70. Aj, Ay, Ist and 2nd antennae of Nauplius ; Ab, abdomen ; Ant, antenna of Cypris ; /, undifferentiated cells ; /, frontal horn ; G, glands of Cypris ; HT, tendon of Cypris ; M7, mandible ; 7’, tentacles. part, immediately beneath the stomach of the crab (Fie. 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 (c./), 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 Sacculina 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 crab’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 “Sacculina 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 Sacci- ment of the “ Sacculina interna,” lina overlying it, x 2. ¢.t, ‘‘ Cen- x 2. 6b, Body of Sacculina ; c.t, tral tumour” of the parasite ; “central tumour”; d.i, d.s, in- dai, d.s, inferior and superior ferior and superior diverticula of diverticula of alimentary canal alimentary canal of host ; 0, open- of host ; ”, ‘‘ nucleus,” or body- ing of perivisceral cavity of Saccu- rudiment of Sacculina; 7, its lina ; 7, its roots. roots; «, definitive position of 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 Sacculina 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. men,and the paired compound eyes are borne upon stalks. The eight thoracic limbs are all very similar; they are built on the typi- cal biramous plan, and each carries a bract; they have l been compared, owing to their flattened, expanded shape, to the 1 Claus, Arb. Inst. Wien, viii., 1889, p. 1. 1 76.—Nehalia geoffroyi, Oe 205 ALLA OF lst and 2nd antennae ; Ad. 7, Ab.G, 1st and 6th abdo- minal appendages ; 4A.G, antennary gland; (, half of caudal fork ; #, eye; G, ventral ganglionic chain ; /1, heart ; 7, intestine ; Z, upper liver-diverticulum ; MW, adductor muscle of halves of carapace ; JILY, palp of Ist maxilla ; O; ovary; R, rostrum. (After Claus.) Ii2 CRUSTACEA——EU MALACOSTRACA CHAP. foliaceous limbs of the Phyllopods. The abdominal appendages are also biramous. The heart is greatly elongated, stretching through thorax and abdomen; there are present both the anten- nary excretory glands characteristic of adult Malacostraca and the maxillary glands characteristic of adult Entomostraca, and both the posterior and anterior livers characteristic of the two Orders respectively are present. This combination of characters justifies the belief that Nebalia represents a primitive form, standing to some extent in an intermediate position between Entomostraca and Malacostraca, but it may be doubted if the ' special relationship to the Phyllopoda, claimed on the strength of the foliaceous appearance of the thoracic limbs, can be legitimately pressed. Nebalia shows the clearest signs of relationship to the other primitive Malacostraca, and especially to the Mysidae, which it resembles not only in general form and in the essentially biramous character of its appendages, but also in many embryo- logical points and in the similarity in development of the brood- pouch." A large number of very ancient palaeozoic fossils are known which are placed provisionally with Nebalia in the Division Phyllocarida, and some of these are no doubt closely related to the existing isolated genus. Hymenocaris from the Cambrian. SERIES 2. EUMALACOSTRACA. Before entering on a description of the members of this Series it is necessary to introduce and justify a new scheme of classification which has been proposed by Dr. W. T. Calman. This scheme necessitates the abandonment of the old Order Schizopoda, and also ignores the distinction which used to be considered fundamental between the sessile-eyed Crustacea (Edriophthalmata) and the stalk-eyed forms (Podophthalmata). The old group of Schizopoda, to which Nebalia and the isolated form Anaspides, to be considered later, are undoubtedly related, represent very clearly the stem-forms from which the various branches of the Malacostracan stock diverge. No doubt they are themselves specialised in many directions, since they are a dominant group in present day seas, but their organisation is ! Robinson, Quart. J. Mier. Sci. 1., 1906, p. 383. Vv CLASSIFICATION OF MALACOSTRACA 113 fundamentally of a primitive type. We see this especially in the comparative absence of fusion or reduction of the segments of the body externally and of the nervous system internally, and in the simple undifferentiated character of the trunk-limbs, all of which conform to the primitive biramous type. The most anterior thoracic limbs of the Schizopods are of particular interest. In the higher Malacostraca three of these limbs are usually turned forwards towards the mouth to act as maxilli- pedes, and the most anterior of all, the first maxillipede, is apt, especially in the Decapoda, to take on a flattened foliaceous form owing to the expansion of the basal segments to act as gnathobases (see Fig. 1, A, p. 10). Now this appendage in the Schizopods preserves its typical biramous character, and resembles the succeeding thoracic limbs, but in many of the species the basal joints show a tendency to be produced into biting blades (Fig. 1, E, p. 10), thus indicating the first step in the evolution of the foliaceous first maxillipede of the Decapoda. The primitive character of the Schizopods is also indicated by the fact that most of the Decapoda with uniramous limbs on the five hinder thoracic segments pass through what is known as the “ Mysis stage ” in development, when these limbs are biramous, the exo- podites being subsequently lost in most cases. The “Schizopoda” include a very large number of pelagic Crustacea of moderate size, which superficially appear to resemble one another very closely. The slender, elongated body, the presence of biramous limbs on all the thoracic and abdominal segments, and the possession of a single row of gills at the bases of the thoracic lmbs, are, generally speaking, typical of the families Mysidae, Lophogastridae, Eucopiidae, and Euphausiidae, which go to make up the old Order Schizopoda. It has, however, been pointed out first by Boas,’ and sub- sequently by Hansen and Calman,” that the Euphausiidae are in many respects distinct from the other three families, and agree with the Decapoda, while the Eucopiidae, Lophogastridae, and Mysidae agree with the Cumacea, Isopoda, and Amphipoda. It has, therefore, been suggested by these authors that the classification of the Malacostraca should be revised, and Calman (Joc. cit.) has brought forward the following scheme :— 1 Morphol. Jahrb. vili., 1883, p. 485. . 2 Ann. Mag. Nat. Hist. (7), xili., 1904, p. 144. VOL. IV I Ma bya CRUSTACEA—SYNCARIDA CHAP. The division PERACARIDA, including the Eucopiidae, Lopho- gastridae, and Mysidae (= Mysidacea), the Cumacea, Isopoda, and Amphipoda, is characterised by the fact that when a carapace is present it leaves at least four of the thoracic segments free and uncoalesced: by the presence of a brood-pouch formed from the oostegites on the thoracic limbs of the female: by the elongated heart: by the few and simple hepatic caeca: by the filiform spermatozoa: and by the direct method of development without a complicated larval metamorphosis. The biting face of the mandible has a movable joint, the “ lacinia mobilis.” The division Eucaripa, on the other hand, including the Euphausiidae and the Decapoda, shows the converse of these characters. The carapace coalesces with all the thoracic seg- ments, there is never a brood-pouch formed from oostegites, the hepatic caeca are much ramified, the heart is short, the spermato- zoa are spherical with radiating pseudopodia, the development is indirect with a complicated metamorphosis, and the mandible is without a lacinia mobilis. Corresponding divisions are made by Calman to receive the other Malacostraca, namely, the PHyLLocaripA for Nebalia, the SYNCARIDA for Anaspides, and the HopnLocaripa for the Stomatopoda or Squillidae. The important array of characters which separates the Euphausiidae from the other Schizopods and unites them with the Decapoda can no longer be neglected, and the consideration of Anaspides and its allies will further emphasise the extreme difficulty of retaining the Schizopoda as a natural group. In the sequel Calman’s proposed scheme will be adopted. DIVISION 1. SYNCARIDA. There is no carapace, and all the eight thoracic segments may be free and distinct. Eyes may be pedunculate or sessile. The mandible is without a lacinia mobilis. There is no brood-pouch, the eggs being deposited and hidden after fertilisation. The spermatozoa are filiform, the hepatic caeca very numerous, and the heart tubular and elongated, with ostia only in one place in 1 The lacinia mobilis is a movable tooth-like structure jointed on to the biting face of the mandible. v ANASPIDACEA Tae the anterior thoracic region, The auditory organ is at the base of the first antennae. Order. Anaspidacea. Fam. 1. Anaspididae.—The mountain-shrimp of Tasmania, Anaspides tasmaniae, was first described by Thomson! in 1893 from specimens taken in a little pool near the summit of Mount Wellington ; it was redescribed by Calman,’ who drew attention to its remarkable resemblance to certain Carboniferous fossils of Europe and N. America (Gampsonyx, Palaeocaris, ete.). The creature appears to be confined to the deep pools of the rivers and tarns on the mountains of the southern and western portions of Tasmania.’ The waters in which it occurs are always cold and absolutely clear, and there is no record of its living at altitudes much below 2000 feet, while it frequently occurs at 4000 feet. The body may attain upwards of two inches in length ; it is deeply pigmented with black chromatophores, and it is held perfectly horizontal without any flexure. The animal rarely swims unless disturbed, usually walking about on stones and water-plants at the bottom of deep pools. In walking the endopodites of the thoracic limbs are chiefly instrumental, but they are assisted by the exopodites of the abdominal limbs. When frightened the shrimp can dart rapidly forwards or sideways by the strokes of its powerful tail-fan, but it never jumps backwards as do the other Malacostraca. It appears to browse upon the aigal slime covering the rocks and on the submerged liver-worts and mosses, but it does not refuse animal food, even feeding on the dead bodies of members of its own species. The thoracic limbs, which are all biramous except the last pair, carry a double series of remarkable plate-lke gills on their coxopodites. The slender and setose exopodites of the thoracic limbs are respiratory in function, being kept im continual motion even when the animal is at rest, and serving to keep up a current of fresh water round the gills. Anaspides shows a remarkable combination of structural characters, some of which are peculiar, while others are possessed in common with the Peracarida or Eucarida. The chief peculiar 1 Trans. Linn. Soc. (2), vi., 1894-1897, p. 285. ‘ 2 Trans. Roy. Soc. Edinburgh, xxxviii., 1897, p. 787. 3G. Smith, Proc. Roy. Soc. 1908. L10 CRUSTACEA——-SYNCARIDA CHAP. characters are the entire absence of a carapace, and the freedom of the eight thoracic segments, with eight free thoracic gangha in the nerve-cord; the peculiar double series of plate-like gills; the structure of the alimentary canal; and the fact that the eggs, instead of being carried in a brood-pouch, or affixed to the abdominal limbs, are deposited under stones and among water-plants.’ er: al Pc a Pl Se ee 2 y \ |; . Fic. 77.—Anaspides tasmaniae in natural position for walking, x 1. ‘The last two pereiopods point backwards and are overlapped by the first two pleopods. The Peracaridan features, uniting it especially with the Mysidacea, are the structure of the elongated heart, the filiform spermatozoa, and the fact that no complicated metamorphosis 1s passed through, the young hatching out in a condition similar to, though possibly not identical with, the adult form. The Eucaridan, especially Decapodan, features are the presence of an auditory sac on the basal joint of the antennules, 1 This characteristic is found in the Crustacea elsewhere only in the Argulidae and certain Euphausiidae. Vv PARANASPIDES AND KOONUNGA 76 and the modification of the endopodites of the first two abdominal appendages in the male to form a copulatory organ. A type of a new genus of this family was found by me in the littoral zone of the Great Lake of Tasmania at an elevation of 3700 feet, and named Paranaspides lacustris. This little shrimp (Fig. 78), which does not appear to grow to more than an inch in length, is totally different in appearance from Anaspides, being pale green and transparent, with a very marked dorsal hump as in JMysis, to which it bears a very Fic. 78.—Paranaspides lacustris, x 4. a, a?, First and second antennae ; Ad. /, first abdominal segment ; ep, epipodites or gills on the thoracic legs ; md, mandible ; P1.1, first pleopod ; 7, telson; 7h.8, eighth free thoracic segment ; U, uropod, or sixth pleopod. striking superficial resemblance. It leads a more active swim- ming life than Anaspides, and with this habit is correlated the flexure of the body and the greater size of the tail-fan and the scale of the second antenna. The mandible is peculiar in being furnished with a four-jointed biramous palp, while that of Anas- pides is three - jointed and uniramous, and the first thoracic appendage is provided with a setose biting lobe on the ante- penultimate joint, thus more resembling a maxillipede. In other respects it agrees essentially in structure with Anaspides. Fam. 2. Koonungidae.— The sole representative of this family, Koonunga cursor, has been recently described by Mr. O. A. Sayce,’ of Melbourne University, from a small stream some 1 The Victorian Naturalist, xxiv., 1907, p. 117. 118 CRUSTACEA——PERACARIDA CHAP. miles to the west of Melbourne. Although plainly belonging to the Anaspidacea, this interesting little animal, which only measures a few millimetres in length, and follows a similar habit to Anaspides, running about with its body unflexed, differs from all the other members of the Division in possessing sessile instead of stalked eyes, in the first thoracic segment being fixed to the head, and in a number of minor anatomical points. It is impossible at present to assign the Carboniferous forms (Gampsonyx, Palaeocaris, etc.) to their exact position in the Division, but it seems that they agreed more closely with Anaspides than with the other two genera. From the position in which the fossils are preserved, it would appear that they followed a similar walking habit to Anaspides, and that the body was unflexed, DIVISION 2. PERACARIDA. The carapace, when present, leaves at least four of the thoracic somites distinct; the first thoracic segment is always fused with the head. The eyes are pedunculate or sessile. The mandible possesses a lacinia mobilis. A brood-pouch is formed in the female from oostegites attached to the thoracic limbs. The hepatic caeca are few and simple; the heart 1s elongated and tubular; the spermatozoa are filiform, and development takes place without a complicated metamorphosis. Order I. Mysidacea. The Mysidacea, although pelagic, are not very often met with in the true plankton on the surface; they generally swim some way below the surface, going down in many cases into the abysses. For this reason they thrive excellently in aquaria, and the common Mysis vulgaris is often present in such numbers in the tanks at the Zoological station at Naples as to damage the other inmates by the mere press of numbers. The Mysidacea, like the majority of the Peracarida, undergo a direct development, and hatch out with the structure of the adult fully formed. Many of the Mysidacea bear auditory sacs upon the sixth pair of pleopods, a characteristic not found in the Euphausiacea. Fam. 1. Eucopiidae.——The curious form Hucopia australis . v MYSIDACEA UO) (Fig. 79) described by Sars,’ may be chosen as an example of the Mysidacea. The pecuharity of this form consists chiefly in the immense elongation of the endopodites of the fifth, sixth, and seventh thoracie appendages. Characteristic of the Mysidacea is the freedom of the hinder thoracic segments from fusion with the carapace, other- wise this animal is seen closely to resemble the Huphausia figured (Fig. 102). Hucopia australis, like so many of the Mysidacea, is a Fig. 79.—Hucopia australis, young female, x 3. A, Ist antenna; Ad.1, Ist abdominal segment ; Ab.6, 6th abdominal appendage; /7, eye; 7, telson; Th, 5th thoracic appendage. (After Sars.) deep-sea animal, being brought up with the dredge from over 1000 fathoms; it is very widely distributed over the Atlantic Ocean. Fam. 2. Lophogastridae. — The members of this family (Lophogaster, Gnathophausia) agree with the Kucopidae in the possession of branched gills on some of the thoracic limbs, in the absence of auditory sacs on the sixth pair of pleopods, in the presence of normally developed pleopods in both the male and female, and in the brood-lamellae being developed on all seven of the thoracic hmbs. The endopodites of the posterior thoracic limbs are, however, of a normal size. Fam. 3. Mysidae.—These differ from both the foregoing families in the absence of gills, in the presence of an auditory sac on the sixth pleopods, in the reduction of the other pleopods in the female, and in the brood-lamellae being developed only on the more posterior pairs of thoracic limbs. A number of closely 1 Challenger Reports, vol. xiii., 1885, p. 55. 120 CRUS TACHA —PHRACAR TDA CHAP. related genera compose this family, of which Jlysis, Boreomysis, and Siriella may be mentioned. J/ysis oculata, var. relicta, 18 a freshwater form from the lakes of northern and central Europe. Order II. Cumacea.' The Cumacea are a group of small marine animals rarely attaining an inch in length, which agree with the Mysidacea in the characters noted above as diagnostic of the Division Peracarida ; they possess, however, in addition a number of peculiar properties, and Sars beleves them to be of a primitive nature showing relationship to Nebalia, and possibly to an ancestral Zoaea-like form. They follow a habit similar to that of the Mysidacea, being caught either in the surface-plankton or in great depths, many of the deep-sea forms being blind. They are, however, not true plankton forms, and they appear to attain a greater development both in point of variety and size in the seas of the northern hemisphere. The thoracic limbs may be biramous, but there is a tendency among many of the genera to lose the exopodites of some of the thoracic legs, an exopodite never being present on the last few eae ee i eee limbs of the female and on Diastylis stygia, x 12. A, 2nd the last in the male. In the Cumidae seca eae Sala the four posterior pairs in both sexes have no exopodites. The first three thoracic appendages following the maxillae are distinguished as maxillipedes; they are uniramous, and the first pair carries an Abi6=--=—-#: 1 Sars, “ Crustacea of Norway,” iii., 1900. Vv FAMILIES OF CUMACEA 120 epipodite and a large gill upon the basal joints. Pleopods are only developed in the male sex. The flagellum of the second antennae in the male may be enormously elongated, as in the Atlantic deep-sea species shown in Fig. 80, so as to exceed in length the rest of the body. Fam. 1. Cumidae.—No sharp demarcation between thorax and abdomen. Four posterior pairs of legs in both sexes with- out exopodites. Male with five well-developed pleopods in addi- tion to the uropods. Telson wanting. Cuma, Cyclaspis, ete. Fam. 2. Lampropidae.— Body -form resembles that of Cumidae. All the thoracic limbs except the last have exopodites. The male has three pairs of pleopods. Telson present. Lamprops, Platyaspis, ete. Fam. 3. Leuconidae—Pody-form similar to above. Male has only two pairs of pleopods. Mouth-parts peculiar, much less setose than in other families. Telson absent. eucon, Eudorella. Fam. 4. Diastylidae.— Anterior part of thorax sharply marked off from posterior part. Male has two pairs of pleopods. Telson present. Diastylis (Fig. 80). D. goodsivi from the Arctic ocean measures over an inch in length. Fam. 5. Pseudocumidae—Rather similar to Diastylidae, but differ in reduced size of telson and presence of exopodites on third and fourth thoracic legs of female. This family is represented by three very similar marine forms of the genus Pseudocuma; but, as Sars has shown,’ the Caspian Sea contains thirteen peculiar species, only one of which can be referred to the genus Pseudocuma, while the rest may be partitioned among four genera, Pterocuma, Stenocuma, Caspiocuma, Schizorhynchus. Order III. Isopoda. The Isopoda and the Amphipoda are frequently classed together as Arthrostraca or Edriophthalmata, owing to a number of features which they share in common, as, for instance, the sessile eyes which distinguish them from the podophthalmatous Schizopoda and Decapoda, the absence of a carapace, and the thoracic limbs which are uniramous throughout their whole existence. For the rest, in the presence of brood-plates and the other diagnostic 1 Sars, ‘‘Crustacea Caspia,”’ Bull. Acad. Imp. Sci. St. Pétersbowrg, series 4, xxxvi., 1894, and ‘‘ Crustacea of Norway,” iii., 1900, p. 120. P22 CRUSTACEA—PERACARIDA CHAP. characters, they are plainly allied to the other Peracarida, and an easy transition is effected from the Mysidacea to the Isopoda through the Chelifera or Anisopoda. Only one thoracic segment is usually fused with the head, the appendage of this segment being the maxillipede; in the Chelifera among Isopoda, and the Caprellidae among Amphipoda, two thoracic segments are fused with the head. The Isopoda are distinguished from the Amphipoda by the dorso-ventral flattening of the body, as opposed to the lateral flattening in the Amphipoda, by the posterior position of the heart, and by the branchial organs being situated on the abdominal instead of on the thoracic limbs. The Isopoda, following Sars’! classification, fall into six sub- orders—the Chelifera, Flabellifera, Valvifera, Asellota, Oniscoida, and Epicarida,—to which must be added the Phreatoicidea. Sub-Order 1. Chelifera. The Chelifera, including the families (1) Apseudidae and (2) Tanaidae, are interesting in that they afford a transition between the ordinary Isopods and the Mysidacea. The important features in which they resemble the Mysidacea are, first, the fusion of the first two thoracic segments with the head, with the coincident formation of a kind of carapace in which the respiratory functions are discharged by a pair of branchial lamellae attached to the maxillipedes ; and, second, the presence of very small exopodites on the first two thoracic appendages of the Apseudidae. The second pair of thoracie limbs, é.e. the pair behind the maxillipedes, are developed both in the Apseudidae and Tanaidae into a pair of powerful chelae, and these frequently show marked sexual differences, being much more highly developed in the males than in the females. The biramous and flattened pleopods are purely natatory in function, and the uropods or pleopods of the sixth pair are terminal in position and slender. Both families, of which the Apseudidae contain the larger forms, sometimes attaining to an inch in length, are littoral in habit, or occur in sand and ooze at considerable depths, many of the genera being blind. Many Tanaids (eg. Leptochelia, Tanais, 1 «Crustacea of Norway,” vol. ii., Isopoda, 1899, in which many references to literature will be found. Vv ISOPOPODA—_-CHELIFERA SEXUAL DIMORPHISM 123) Heterotanais, ete.) live in the algal growths of the littoral zone, and being highly heliotropic they are easy to collect if a basinful of algae is placed in a strong light. The females carry the eggs about with them in a brood-pouch formed, as is usual in the Peracarida, by lamellae produced from the bases of the thoracic hmbs. The males on coming to maturity do not appear to grow any more, or to take food, their mouth-parts frequently degenerating and the alimentary canal being devoid of food. They are thus in the position of insects which do not moult after coming to maturity ; and, as in Insects, the males are apt to show a kind of high and low dimorphism—certain of the males being small with secondary sexual characters little different from those of the females, while others are large with these characters highly developed. Fritz Miller, in his Facts for Darwin, observes that in a Brazilian species of Leptochelia, ap- parently identical with the European L. dubia, the males oceur under two totally distinct forms—one in which the chelae are greatly developed, and another in which the chelae resemble - those of the female, but the antennae in this form are provided with far longer and more numerous sensory hairs than in the first form. Miiller suggested that these two varieties were produced by natural selection, the characters of the one form com- Fic. 81.—Apseudes spinosus, 6, x 15. A, Ist antenna; Ad, 6th abdominal appendage; 7’, 2nd thoracic appendage. (After Sars. ) pensating for the absence of the characters of the other. > -a.b abdomen. Beneath, it is usually quite mem- , 1G. 174.—Diagram- branous, guarded only by a sort of collar formed matic ventral view by the raised border of the anterior portion of See sy the abdomen at the point of insertion. In — Labium; m, max- some Spiders, however (Dysderidae), there is a Sane posterior sternal plate, the “plagula,’ closely — sternum; wu, un- corresponding with the labium in front, which ce ee partly embraces the pedicle. In Hermippus Anal tubercle; ¢, (Zodariidae) the plagula is detached from the a Ment sternum, and is succeeded posteriorly by two Be eee 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 Liphistivs 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. 318 ARACHNIDA—ARANEAE CHAP, That these scuta are sometimes indicative of an obsolete seginentation would seem likely from the study of the remarkable species, Tetrablemma mediocu- Wie latum (Fig. 176), described by | Pickard - Cambridge, — from ee Ceylon. In addition to large Fol dorsal and ventral scuta, the : sides and posterior extremity A are guarded by smaller scuta, the disposition of which is well seen in the figure. The normal smooth ab- eee domen presents dorsally no 6 Ze very striking features. In Fic. 175.—Spider profiles. 1, Poltys ideae ; species of variegated colora- 2, Phoronedia 7-aculeata & 3, Ariamnes tion there is very generally flagellum ; 4, Stegosoma testudo ; 5, For- i 5 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 Fic. 176.— Tetrablenma medioculatum, much two Kinds, lung-books and singel Ay Fosters ‘isn 5B of 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 Jops. 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 slight 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 in 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 compleated, 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, and 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,¢), is often observable, projecting between the anterior spinnerets. The “anal tubercle ” (Fig. 174, at), 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.1 _ 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 applied 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 Jateral, 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 ‘ insects pierced by the ungues. Fie. 177, — Front The crescent-shaped unguis is tapering and view of Teaxtrix 5 denticulata. x Smooth, except for the presence, on the posterior ee = ae surface, of one or two feebly dentated ridges. 3, paturon, and Near its free extremity there is a small orifice ena ofcheli- Jeading 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 Ber 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 a 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—The 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 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 Fic. 178. —Pedipalp of Tegenuria domestica & . their inclination towards the x 5. 1, Coxa; 2, maxilla; 3, trochanter ; labium are of considerable z ae a eo Cp Abie Ar She taxonomic importance. The inner border of the maxilla is furnished with a tuft of hairs, 1 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 NG 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,’ on _ its ture ; 5, style; 6, haematodocha ; 7, alveolus ; . 8 tibia. 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 XIII APPEN DAGES 3 NO Ww iis tube within the bulb, ending in a blind sae, 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 applied directly to the genital orifice. The receptaculum and its tube being 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 cozu, trochanter, femur, patella, tibia, metatarsus, and tarsus.’ In a few cases, through the presence of false articulations, @.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. a 2A: 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 shagey 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 deutated, 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 ” (Fig. 180, 5), 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 “cribellum,”’, but -~ this will be dealt with when we reach the systematic Frc. 180.—Spider tarsi. 1, Tarsus of Lpeira showing portion of the subject. three claws and supplemental serrate hairs (@) ; i 2, tarsus of a Thomisid Spider, with two claws ; The general direction 3, 3a, lateral and dorsal view of tarsus of an 4,1], by , : by the legs, the Attid Spider, showing scopula at 0. taken ) ae be 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 3 i) ut 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 jomts. 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 »,, 181, spinnerets of Hpeira appendages, and additional play is given — diademata. A, Ventral view to their action by the presence of articula- Cae o ee gnified ; C, : 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 1s 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 B es the form of a SSS = —— double sieve-like a__ = = K\\ plate, the “ cri- bellum.” — This : is always corre- ie ee j lated with a comb of curved bristles on the metatarsi of the fourth pair of h( os — legs, the “cala- Pt a yee mistrum.” Such importance is i. oe are. Ss ] zi >) T } , } ] } 7 Fic oe: A, Spinnerets of Amaurobius sunilis P. Much agsioned to these enlarged. a, Anus; cr, cribellum; 7.s, inferior spinneret ; S = m.s, median spinneret ; s.s, superior spinneret. B, Part of Organs by Simon, the 4th leg of the same Spider, showing the calamistrum (ca) ne ; on the metatarsus. that the Araneae FE SANA T Ns Wpret Veraeare divided by him according to whether they are present or absent, into CRIBELLATAE and KCRIBELLATAE. This is probably an exaggerated view of the importance of these organs, and the XIII . STRIDULATING ORGANS 3 i) N 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 Theridudae would appear to be inaudible to human ears. Westring ' was the first to discover (1843) a stridulating organ in the small Theridud spider Asagena phalerata. The abdomen, where the pedicle enters it, gives off a chitinous collar, which projects over the cephalothorax, and has the imner 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 Rs Fic. 183.—Stridulating apparatus of Steatoda cephalothorax. A similar bipunctata, 6. Muchenlarged. A, Ridged organ has been sinee found and toothed abdominal socket ; B, striated ‘ : : : area on the cephalothorax ; C, profile of in various allied spiders, of tne spider, x5. 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., 1843, p. 349. 2J. Linn. Soc. xv., 1881, p:. 155. 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.t The sound resembled that ob- tained by “drawing the back of a knife along i= the edge of a strong Fic. 184. — Chilobrachys stridulans in stridu- comb.” re attitude. After Wood-Mason. Natural Subsequently certain Sicarid 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 he 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. XIII 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 Aviculariidae possess the power of hearing. In the inoffensive stridulating Sicariid 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. 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, e), 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 is en- larged, and fluids from the pharynx are pumped up into it. The canal thus far is lned by chitin, like the exterior of the body, and forms a sort of compli- cated mouth-apparatus. The Mesenteron les partly in Fic. 185.—Diagram showing the ana- tomy of the cephalothorax of a Spider. Therightalimentary diverti- culum has been removed. a, Aorta ; c, left diverticulum with secondary caeca; e, endosternite ; oes, oeso- phagus, descending to the mouth ; s, sucking stomach ; sh, dorsal shield of sucking stomach. the cephalothorax and partly in the abdomen. The thoracic portion, 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 (Hpeir'a) 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. XTII * VASCULAR SYSTEM 331 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 ning. 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 les 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. 332 ARACHNIDA—ARANEAE CHAP. 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 itestine, and presently forks into two main branches, which run along either side of the sucking stomach, near the front of which they bend eae hy im ll ase . LL’ — Ve ee PS ReDE ee 18 Fic. 186.—Diagram of a Spider, Hpeira 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 ; 6, anus ; 7, dorsal muscle of sucking stomach ; 8, caecal prolongation 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 dendriform silk-glands ; 18, spinnerets or mammillae ; 19, distal joint of chelicera ; 20, poison- gland ; 21, eye; 22, pericardium ; 25, vessel bringing blood from lung-sae to peri- cardium ; 24, artery. suddenly downwards and end in a “ patte d’oie,” as Causard ’ expresses it—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 dole.” 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. > CL OS REPRODUCTIVE AND NERVOUS SYSTEMS 333 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 saes 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 eggs 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 little globular packets known as “ spermato- phores.” Nervous System.—The Spider’s central nervous system 1s 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 throngh 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, it 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. xi SPINNING GLANDS 335 Spinning Glands.—Spiders vary greatly in their spinning powers. Some only use their silk for spinning a cocoon to pro- tect their eggs, while others employ it to make snares and _ re- treats, to bind up their prey, and to anchor themselves to spots to which they may wish to return, and whence they “drag at each remove a lengthening chain.” All these functions are performed by the silk-glands of the Orb- weavers, and hence it is with them that the organs have attained their greatest perfection. We may conveniently take the case of the common large Garden-spider, Epeira diademata. The glands occupy the entire floor of the abdomen. They have been very thoroughly investigated by Apstein,' and may be divided into five kinds. On either side of the abdomen there are two large “ ampul- laceal” glands debouching on “ spigots,’ one on the anterior, and one on the middle spinneret ; there are three large “aggregate ” glands which all terminate on spigots on the posterior spinneret ; and three “ tubuli- form” glands, two of which have their orifices on the posterior, and one on the middle spinneret. Thus, in the entire abdomen there are sixteen large glands, terminating in the large fusulae known as spigots. In addition to this there are about 200 “ piriform” glands whose open- ings are on the short conical fusulae of the posterior and anterior spinnerets, and =a about 400 “aciniform” glands which Fic. 187.—Spinning glands. debouch, by cylindrical fusulae, on the relate ais ae, middle and posterior spinnerets. Thus there are, in all, about 600 glands with their separate fusulae in the case of Epeira diademata. The great number of orifices from which silk may be emitted has given rise to the widespread belief that, fine as the Spider's line is, it is woven of hundreds of strands. This is an entire misconception, as we shall have occasion to show when we deal with the various spinning operations. A few families are, as has already been stated, characterised by the possession of an extra spinning organ, the cribellum, and 1 Arch. f. Naturg. 55 Jahrg., i., 1889, p. 29. 336 ARACHNIDA— ARANEAE CHAP. the orifices on this sieve-lhke plate lead to a large number of small glands, the “ cribellum glands.” Respiratory Organs.—Spiders possess two kinds of breath- ing organs, very different in form, though essentially much alike. They are called respectively “ lung-books ” and “ tracheae.” The Theraphosae (and Hypochilus) have four lung-books, while all other spiders, except Mops, have two. Tracheae appear ‘to be present almost universally, but they have not been found in the Pholeidae. The pulmonary stigmata lead into chambers which extend forwards, and which are practically filled with horizontal shelves, so to speak, attached at the front and sides, but having their posterior edges free. These shelves are the leaves of the lung- book. Each leaf is hollow, and its cavity is continuous, anteriorly and laterally, with the blood-sinus into which the blood from the various parts of the Spider's body is poured. The minute structure of the leaf is curious. Its under sur- face is covered with smooth chitin, but from its upper surface rise vast numbers of minute chitinous points whose summits are connected to form a kind of trellis-work. The roof and floor of the flattened chamber within are connected at intervals by columns. The pulmonary chamber usually contains from fifteen to twenty of these leaves, and the two chambers are always connected internally between the stigmata. The tracheae are either two or four (Dysderidae, Oonopidae, Filistatidae) in number, and their stigmata may be separate or fused in the middle line. Each consists of a large trunk, pro- jecting forwards, and giving off tufts of small tubes which lose themselves among the organs of the abdomen, but do not ramify. In the tracheae of Argyroneta’ a lateral tuft is given off im- mediately after leaving the stigma, and another tuft proceeds from the anterior end. Histologically the main trunk of the trachea is precisely like the general chamber of the pulmonary sac, and differs greatly from the trachea of an insect. Cephalothoracic Glands.—In addition to the generative glands and the so-called “ liver” which occupy so large a portion of the abdomen, there are, in Spiders, certain glandular organs situated in the cephalothorax which call for some notice, These are the coxal glands and the poison-glands. 1 M‘Leod, Bull. Ac. Belg. (3), iii., 1882, p. 779. XU COXAL AND POISON GLANDS 337 The COXAL GLANDS are two elongated brownish-yellow bodies, situated beneath the lateral diverticula of the stomach, and between it and the endosternite. They present four slight pro- tuberances which project a short distance into the coxae of the legs. The glands appear to be ductless, but their function is thought to be excretory. They were first observed in the Theraphosae. All Spiders possess a pair of POISON-GLANDS, connected by a narrow duct with a small opening near the extremity of the fang of the chelicerae. The glands are sac-like bodies, usually situated in the cephalothorax, but sometimes partially (Clubiona) or even entirely (Mygale) in the patura, or basal joints of the chelicerae. Each sac has a thin outer layer of spirally-arranged muscular and connective tissue fibres, and a deep inner epithelial layer of glandular cells. The cavity of the gland acts as a reservoir for the fluid it secretes. The virulence of the poison secreted by these glands has been the subject of much discussion, and the most diverse opinions have been held with regard to it. The matter is again referred to on p. 360. VOL. IV Z CEA PaaRi ok PY, ARACHNIDA EMBOLOBRANCHIATA (CONTINUED )—ARANEAE (CONTINUED) HABITS——ECDYSIS—-TREATMENT OF YOUNG—MIGRATION——WEBS-—— NESTS —— EGG-COCOONS — POISON —— FERTILITY —_- ENEMIES —— PROTECTIVE COLORATION—MIMICRY—-SENSES—INTELLIGENCE ——MATING HABITS—FOSSIL SPIDERS EARLY LIFE OF SPIDERS. Ecdysis or Moulting.—Spiders undergo no metamorphosis— that is to say, no marked change of form takes place, as is so often the case among Insects, in the period subsequent to the hatching of the egg. This fact; by the by, is a great trouble to collectors, as it is generally extremely difficult, and sometimes quite impossible, to identify immature specimens with certainty. But although unmistakably a spider as soon as it leaves the egg, the animal is, at first, in many respects incomplete, and it is only after a series of moults, usually about nine in number, that it attains its full perfection of form. Until the occurrence of its first moult it is incapable of feed- ing or spinning, mouth and spinning tubes being clogged by the inembrane it then throws off. It is at first pale-coloured and less thickly clothed with hairs and spines than it eventually becomes, and the general proportions of the body and the arrange- ment of the eyes are by no means those of the adult in miniature, but will be greatly modified by unequal growth in various direc- tions. It speedily, however, attains its characteristic shape and markings, and after one or two ecdyses little alteration is to be noticed, except increase in size, until the final moult, when the spider at length becomes sexually mature. 338 CHAP, XIV ARANEAE—MOULTS 339 The first moult takes place while the newly-hatched spider is still with the rest of the brood either in or close to the “ cocoon ” or ego-bag. M‘Cook? thus describes the conclusion of the opera- tion in the case of Agelena naevia :-— “While it held on to the flossy nest with the two front and third pairs of legs, the hind pair was drawn up and forward, and the feet grasped the upper margin of the sac-like shell, which, when first seen, was about half-way removed from the abdomen. The feet pushed downwards, and at the same time the abdomen appeared to be pulled upward until the white pouch was gradually worked off.” The later moults are generally accomplished by the spider collecting all its legs together and attaching them with silk to the web above, while the body, also attached, hangs below. The old skin then splits along the sides of the body, and the animal, by a series of violent efforts, wriggles itself free, leaving a com- plete cast of itself, imcluding the legs, suspended above it. Fora day or two before the operation the spider eats nothing, and im- mediately upon its completion it hangs in a hmp and helpless condition for a quarter of an hour or so, until the new integu- ment has had time to harden. It is not unlikely that the reader has mistaken these casts for the shrivelled forms of unlucky spiders, and has had his sympathies aroused, or has experienced a grim satisfaction, in consequence—an expenditure of emotion which this account may enable him to economise in future. Limbs which the animal has accidentally lost are renewed at the time of moulting, though their substitutes are at first smaller than those they replace. On the other hand, the struggle to get rid of the old skin sometimes results in the loss of a limb, and the spider is doomed to remain short-handed until the next ecdysis. Until the last moult the generative apertures, which are situated under the anterior part of the abdomen, are completely sealed up. Their disclosure is accompanied, in the case of the male, by a remarkable development of the last joint of each pedipalp, which becomes swollen and often extremely compli- cated with bulbs, spines, and bristles. A mature male spider may at once be distinguished by the consequent knobbed appear- ance of its palps; and the particular form they assume is highly characteristic of the species to which the spider belongs. 1 American Spiders and their Spinning Work, 1i., 1890, p. 208. ° 340 ARACHNIDA——-ARANEAE CHAP, The number of moults, and the intervals at which they occur, no doubt vary with different species. In the vase of Argiope aurelia, Pollock! has found that the female moults nine times after leaving the cocoon, the first ecdysis occurring after an interval of from one to two months, according to the abundance or scarcity of food. The subsequent intervals gradually increase from about a fortnight to something over three weeks. Behaviour of the Newly-hatched Spider.—The mode of life of a spider just freed from the cocoon will of course vary greatly according to the Family to which it belongs. The EPEIRIDAE are the builders of the familiar wheel or orb- web. Spiders of this Family usually remain together on friendly terms for a week or more after leaving the nest. Most of the time they are congregated in a ball-like mass, perhaps for the sake of warmth, but upon being touched or shaken they im- mediately disperse along the multitudinous fine nes which they have spun in all directions, to reassemble as soon as the panic has subsided. Such a ball of the yellow and black offspring of the large Garden-spider, Hpeira diademata, is no uncommon sight in the early autumn, and the shower of “ golden rain ” that results from their disturbance is not likely to be forgotten if it has ever been observed by the reader. This harmonious family life only continues as long as the young spiders are unable to feed—a period which, in some of the larger species, is said to extend to ten days or a fortnight. Individual life then commences, and each member of the dis- persed group sets up housekeeping on its own account, con- structing at the first attempt a snare in all respects similar, except in size, to those of its parent. Of course the young Spiders have not migrated far, and a bush may frequently be seen covered by the often contiguous nets of the members of a single brood. This, as Dr. M‘Cook thinks, is the true explanation of some of the cases of “gregarious spiders” which Darwin * and other naturalists have occasionally described, though social spiders exist (see Uloborus, p. 411). Very similar habits obtain among the THERIDIIDAE, or line- weaving spiders, a familiar example of which is the pretty little Theridion sisyphium, whose highly-irregular snare may be found on any holly bush during the summer months. 1 Ann. Nat. Hist. (3), xv., W865, p. 459. 2 Voyage of the Beagle. XIV ‘ HABITS OF YOUNG SPIDERS 341 The Lycosrag, or Wolf-spiders, which chase their prey instead of lying quietly in ambush to ensnare it, are exceedingly interest- ing in their treatment of their young. The cocoon, or bag of eges, 18 carried about on all their expeditions, attached be- neath the abdomen, or held by the jaws, and the young spiders, on escaping from it, mount on the mother’s back, and indulge vicariously in the pleasures of the chase from this point of vantage. The empty egg-bag is soon discarded, but the brood continues to ride on the mother’s back for about a week, dis- mounting only to follow her as she enters her little silk-lined retreat in the ground. During this time they appear ",288>4 Pandaw sp. 2, itl, young to require no food, but they at detached ; C, outline of the Spider length begin oa disperse, ine ae removed, (From the living mother gently but firmly re- moving such individuals as are disposed to trespass upon her maternal solicitude longer than she considers desirable. Many young spiders of various Families proceed immediately to seek new hunting-grounds by the aid of the wind, and become for the time being diminutive aeronauts. This habit was observed by the earliest British araneologist, Martin Lister,’ as long ago as 1670, and has been alluded to by many writers since his time. The topmost bar of an iron railing in spring or early autumn will generally be found peopled with minute spiders, and if the day be fair and the wind light, the patient observer may be rewarded by a curious and interesting sight. The spider seeks the highest spot available, faces the wind, and straightens its legs and body, standing, so to speak, upon its toes, its abdomen with its spinning tubes being elevated as much as possible. Streamers of silk presently appear from the spin- 1 Correspondence of John Ray, p. 77. 342 ARACHNIDA—ARANEAE CHAP. nerets and float gently to leeward on the light current of. air. The spider has no power to shoot out a thread of silk to a = distance, but it accomplishes the same result | indirectly by spinning a little sheet or flocculent mass which is borne away by the breeze. When the streaming threads pull with sufficient force the animal casts off, seizes them with its legs, and entrusts itself to the air, whose currents determine the height to which it is carried and the direction of its journey. The duration, however, is not quite beyond the spider’s control, at all events in calm weather, for it can furl its sail at will, hauling in the Fic, 189. —- Young threads “hand-over-hand,” and rolling them up Spider preparingfor into a ball with jaws and palps. Coe This curious ballooning habit of young Spiders is independent of the particular family to which they belong, and it is remarkable that newly-hatched Lycosidae and Aviculariidae, whose adult existence is spent entirely on or under the ground, should manifest a disposition to climb any elevated object which is at hand. The “ Gossamer,” which so puzzled our forefathers, is probably no mystery to the reader. It is, of course, entirely the product of Spider industry, though not altogether attributable to the habit of ballooning above described. Only a small proportion of gossamer flakes are found to contain spiders, though minute insects are constantly to be seen entangled in them. They are not formed in the air, as was supposed long after their true origin was known, but the threads emitted by multitudes of spiders in their various spinning operations have been inter- mingled and carried away by light currents of air, and on a still, warm day in spring or autumn, when the newly-hatched spider- broods swarm, the atmosphere is often full of them. They rise to great heights, and may be carried to immense distances. Martin Lister relates how he one day ascended to the highest accessible point of York Minster, when the October air teemed with gossamer flakes, and “could thence discern them yet exceeding high” above him. Gilbert White describes a shower, at least eight miles in length, in which “on every side, as the observer turned his eyes, he might behold a continual succession XIV WEBS 343 of fresh flakes falling into his sight, and twinkling like stars as they turned their sides toward the sun.” The ascent of a hill 300 feet in height did not in the least enable him to escape the shower, which showed no sign of diminution. | The mortality among very young spiders must be exceedingly great ; indeed, this is indicated by the large number of eggs laid by many species, an unfailing sign of a small proportion of ultimate survivors. We shall have, by and by, to speak of some of their natural enemies, but apart from these their numbers are sadly reduced by the rigours of the weather, and appreciably also by their tendency to cannibalism. D5 magnified. A, Demodea follicu- to swelling and distortion. Hee Eriophyes (Phyptop- Fam. 2. Demodicidae. — The igri tm 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. Demodex possesses eight short, three-jointed legs, each terminated by two claws. The abdomen is much produced, and js 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 2H 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 ete ee ee oe upon decaying animal or vegetable matter, “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 et fifty species. Tyroglyphus sivo 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. | ae Oe Ba WD a 1 See Michael, British Tyroglyphidae, published by the Ray Society, 1901-2. XVIII METASTIGMATA 467 Sub-Order 3. Metastigmata. The four families which constitute this sub-order comprise a large number of Mites in which the tracheae open near the articulation of the legs, and consequently in a somewhat posterior situation. The families are Oribatidae, Argasidae, [xodidae, and Gamasidae. Fam. 1. Oribatidae.—The Oribatidae or “ Beetle-mites” are free-living Acari, with tracheae of which the stigmata are con- cealed by the articulation of the legs. The cephalothorax is distinctly marked off from the abdomen, and bears dorsally two “ pseudo-stigmatic” organs. The rostrum is inserted below the cephalothorax. These Mites gain their popular name from the beetle-like hardness of their integuments. They are oviparous or ovoviviparous. Eyes are always absent. These are small creatures, seldom attaining the twentieth of an inch in length. They are vegetable-feeders (except, perhaps, Pelops), and are to be found in dead wood or vegetable débris, under bark, or among moss and lichen. In winter they often take refuge under stones. It is impossible at present to estimate the number of existing species, for only a few localities have been systematically worked for them, and their small size has prevented their inclusion, in any numbers, in the collections of scientific expeditions. Our knowledge of the group is likely, however, to be largely extended, for it has been found that they reach England alive and in good condition from the most remote regions if moss or other material in which they live is collected when not too dry, and her- metically sealed up in tin Cases. About twenty genera and more than 220 species Fic. 242.—Oribatid Mites. A, Cepheus ocellatus, x 24; B, ventral view of Hoploderma magnum, are at present known. closed, x 20. (After Michael. ) Pelops has much elongated chelicerae, with very small chelae at the end. There are ten species, found in moss and on bushes. Oribata numbers about fifty species, found in moss and on trees. -Notaspis, in which the 468 ARACHNIDA—ACARINA CHAP. last three legs are inserted at the margin of the body, has about thirty species, found among moss and dead leaves. Nothrus is a short-legged genus with flat or concave dorsal plate, often produced into very remarkable spiny processes. There are twenty-two species found under bark and among moss and lichen. Hoploderma (Hoplophora) is remarkable for its power of shutting down its rostrum and withdrawing its legs in a manner which leaves it as unassailable as a tortoise or an armadillo. Though the Oribatidae are all eyeless, they are distinctly sensitive to light, not wandering aimlessly till they reach a shadow, but apparently making straight for a dark spot when subjected to strong illumination. Some species have a curious habit of collecting dirt and débris on their backs, so as entirely to obscure the often very remarkable disposition of the spines and processes with which they are furnished. The next two families include the animals commonly known as Ticks, the largest and most familiar of the Mite tribe. Of recent years they have attracted much attention as the conveyers, to man and domestic animals, of certain diseases due to blood- parasites (see p. 457, n.),and our knowledge of their structure and habits has greatly increased in conse- quence. Hitherto they have generally been considered to constitute a single family, the Ixodidae, but a section of them so differ from the rest as to require their removal to another family, the Arga- sidae, so that it is necessary to employ a super - family name — IxoDOIDEA — to Fig. 243.—Capitulum of Boo- embrace the whole Sehae : philus australis, ventral Ticks are parasitic on mammals, birds, ee SEO a as and reptiles, some shewing a marked m, the mandible or cheli- partiality for a particular host, others EOS digits ™ the being much more catholic in their tastes. Both sexes in the Argasidae, but the females only of the Ixodidae, are capable of great distension, but when unfed they are all somewhat flat animals with laterally extended legs and rather crab-like movement. All Ticks possess a small, movable “false-head ” or capitulum bearing mouth-parts which are exceedingly characteristic of the XVI METASTIGMATA 469 group. The chelicerae are cutting instruments with their distal ends serrated outwardly, and there is always present a hypostome beset with recurved teeth which serve to maintain a firm hold on the tissues into which it is thrust. On either side of the chelicerae are the four-jointed palps, leg-like in the Argasidae, but more rigid and rod-like in the Ixodidae, where their inner margin is often hollowed so as to enclose the chelicerae and hypostome when the palps are apposed. There is a conspicuous pair of spiracles near the coxae of the fourth pair of legs. Fam. 2. Argasidae.—The Argasidae are leathery Ticks without a shield or sewtuwm, and with free, leg-like palps. The eapitulum is never more than partially visible when the adult animal is viewed dorsally. Their hosts are always warm-blooded animals. Two genera are usually recognised, Argas and Ornithodoros, though recent discoveries of new forms have tended towards their fusion. -‘Argas reflenus and A. persicus have been proved to convey a Spirochaete disease to fowls, and the latter, under the name of the “ Mianeh Bue” has long possessed an evil reputation for the “poisonous” effect of its bite on human beings. In Mexico the “ Turicata” Fic. Pe Magen eescren iiare (Ornithodoros turicata) and the “ Gara- Geen Pe ikear pata” (O. megnini) are greatly dreaded, while human “tick fever” on the Congo has been traced to the instrumentality of O. moubata. Fam. 3. Ixodidae.—These are the more familiar Ticks, possessing a scutwim or shield, which covers the whole back of the male, which is capable, there- fore, of little distension, whereas it forms only a small patch on the front part of the body of the distended female. There are ten genera, /zodes, Haema- physalis, Dermacentor, LRhipicentor, Rhipicephalus, Boophilus, Margaropus, Hyalomma, Amblyomma, and Aponomma. Ixodes ricinus is the common English sheep-tick. Species Fic. 245.—Female Sheep-tick, Txodes ricinus. 470 ARACHNIDA—ACARINA CHAP. of Boophilus are parasitic on cattle the world over, and B. annu- latus 1s the transmitter of Texas fever. Rhipicephalus and Amblyomma are large genera which include several species of economic importance. For example, R. sanguineus conveys canine piroplasmosis, and A. hebraewm causes “heart-water” in South African cattle. The genus Aponomma confines its atten- tion to reptiles, and some of its species are exceedingly ornate. Neglecting Margaropus and Rhipicentor, which include only a very few aberrant forms, the following entirely artificial key will serve to differentiate the genera of the Ixodidae :— 1. A pair of eyes on the lateral borders of the scutum 2 No eyes 6 2. Capitulum long, much longer than broad 3 Capitulum short : ‘ 4 3. Unicolorous, ¢ with chitinous plates near anus 2 Fees Generally ornate, ¢ without anal plates : . Amblyomma 4, Generally ornate, ¢ without anal plates, but with en- larged 4th coxae. : . Dermacentor ereolancns 6 with anal plates and onal coxae pe 5. Palpi very short, spiracle circular : : . Boophilus Palpi medium, spiracle comma-shaped_ . 3 Rhipicephalus 6. Capitulum short; 2nd article of alp projecting laterally Huemaphysalis Capitulum long : : : ee 7. Unicolorous, Blonpate, on birds or mammals : Ixodes Generally ornate, “cecil -oval, on reptiles ‘ . Aponomma Neumann has recently revised the Ixodoidea in a series of papers published in the JMlémoires de la Société zoologique de France,’ but the work is not obtainable as a whole. A mono- graph, by Nuttall, Warburton, Cooper, and Robinson, is now in course of publication at the Cambridge University Press.” Fam. 4. Gamasidae.—The Gamasidae are carnivorous Mites, either free-lving or parasitic on animals. The chelicerae are chelate, and the palps are free. The tarsi have two claws, accompanied by a “caruncle” or sucking disc. They are mostly pale-coloured Mites, with a smooth, more or less scutate covering. The three principal sub-familhes are Gamasinae, Uropodinae, and Dermanyssinae. Of the GAMASINAE, Gamasus coleoptratorum is the well-known Beetle-parasite so frequently seen on Geotrupes. It is often con- founded with another species of similar habits, G. crassipes. 1 The first paper appeared in M/ém. Soe. Zool. ix., 1896, pp. 1-44. ” Part I. Argasidae, 1908. 9 * “Ticks, a Monograph of the Ixodoidea. VALE HETEROSTIGMATA—PROSTIGMATA =: Avil The curious Beetle-parasites attached to their victim by a thread belong to the genus Uropoda of- the Uropopinak. The connecting filament, which the Mite can sever at will, for a long time puzzled observers. It was variously construed as a silken cord of attachment, and as a sort of umbilical cord, through which the Mite drew nourishment from the Beetle. On more careful investigation it proved to be connected with the anus of the Mite, and to consist of its consolidated excrement. The DERMANYSSINAE are all parasitic on warm-blooded animals, principally birds and bats. Dermanyssus avium is the common parasite infesting fowls and cage-birds. Sub-Order 4. Heterostigmata. Fam. Tarsonemidae.—This is the sole family of the sub- order. It comprises a number of minute vegetable-feeding Mites which have been little studied, though they are probably the cause of considerable injury to the leaves and buds of plants. Sub-Order 5. Prostigmata. In these Mites the stigmata are situated anteriorly, in the rostrum or the thorax. In the Water-mites the tracheae have atrophied, but these creatures are clearly Trombidudae which have taken to an aquatic life. Fam. 1. Bdellidae.—The Bdellidae are sometimes known as the “Snouted Mites” on account of the very prominent forwardly- directed “capitulum” or false head. They have chelate chelicerae and tactile palps, which are often “ elbowed,” like the antennae of weevils. Eyes may be present or absent. They are usually of a bright red colour, and are free-living and predaceous, though in their larval stages they may often be found attached to the limbs of insects and yyg. 246. — Budella ae spiders. nicola, x about 50. (After Canestrini.) The minute active scarlet Mites of the genus Hupodes and its allies perhaps come within this family. Their legs are six-jointed. 472 ARACHNIDA—ACARINA CHAP, The remaining families of the Prostigmata (Halacaridae, Hydrachnidae, sal Trombididae) all have “raptorial palps, and clawed or piercing chelicerae. Fam. 2. Halacaridae.— This is a small group of marine Mites. In their usually prominent capitulum they resemble the Bdellidae. In some respects they recall the Oribatidae, having hard integuments, and their legs being articulated near the margin of the body. They do not swim, but crawl upon weeds and zoophytes, or burrow in the mud. Fam. 3. Hydrachnidae.—The Hydrachnidae are the Fresh- water Mites. Their legs are provided with long close-set hairs, * and thus adapted for swimming. They are predaceous, and in their young stages are often parasitic on water insects. A familiar example is Atax bonzi, which lives within the shell of the fresh-water mussel. Fam. 4. Trombidiidae. — The predaceous palps of the Trombi- diidae are generally of the “ finger- and-thumb” type. The tarsi are two-clawed, without caruncle. This Fie. 247.—Ataz alticola, x 16. at Bs : . (eee Cancsnat) group may be divided into six sub- families. (i.) The LimnocHARINak or “ Mud-mites” connect the Hydrach- nidae with the typical Trombidiidae. They are usually velvety and of a red colour. They do not swim, but creep. The larva of Limnocharis aquaticus is parasitic on Gerris lacustris. Gi.) The CAECULINAE bear a strong general resemblance to the Harvestmen or Phalangidae. Caeculus is so similar to the Phalangid genus Trogulus that it was considered by Dufour to belong to the same order. (iii.) The TETRANYCHINAE or “ Spin- yg, 248.—Tetranychus gibbo- ning-mites” are phytophagous, and do ao 50. (After Canes- co ‘= rinl. much injury to plants, sucking the sap from the leaves and giving them a_ blistered appearance. Tetranychus telarius is the “ Red-spider” of popular nomenclature. XVIII HETEROSTIGMATA—NOTOSTIGMATA 473 (iv.) The CHEYLETINAE are remarkable Mites with fleshy, semi- transparent body, and enormously developed raptorial pedipalpi, which are extremely formidable weapons of attack. They do not creep or run lke most Mites but proceed by a series of short leaps. Cheyletus is the principal genus. The curious genus Syringophilus, which is parasitic in the interior of birds’ feathers, appears to be a degenerate Cheyletine. (v.) The ERYTHRAEINAE are minute, active Mites, usually red in colour, free-living and predaceous. (vi.) The TROMBIDIINAE include most of the moderate-sized, velvety red Mites which are commonly known as “ Harvest-mites,” and their larvae, the so-called Harvest-bugs, frequently attack man. Zvrombidium holosericeum is a well-known example. Sub-Order 6. Notostigmata.’ This sub-order has been established for the reception of the curious genus Opilioacarus. Fam. Opilioacaridae.— Mites with segmented abdomen, leg- like palps, chelate chelicerae, and two pairs of eyes. There are four dorsal abdominal stigmata. Four .species of the sole genus Opilioacarus have been recorded, O. segmentatus from Algeria, O. italicus from Italy, O. arabiews from Arabia, and O. platensis” from South America. 1 With, Vid. Medd. 1904, p. 187. 2 Silvestri, Redia, ii., 1904, fase. 2, p. 257. APPENDICES TO ARACHNIDA PaAAND bP TARDIGRADA AND PENTASTOMIDA BY ARTHUR: E.- SHIPLEY: M.A. 3ER-S. Fellow and Tutor of Christ’s College, Cambridge, and Reader in Zoology in the University CHAPTER XIX TARDIGRADA OCCURRENCE—ECDYSIS—STRUCTURE—DEVELOPMENT—AFFINITIES— BIOLOGY——DESICCATION——PARASITES——_SYSTEMATIC THE animals dealt with in this chapter lead obscure lives, remote from the world, and few but the specialist have any first-hand acquaintance with them. Structurally they are thought to show affinities with the Arachnida, but their connexion with this Phylum is at best a remote one. Tardigrades are amongst the most minute multicellular animals which exist, and their small size—averaging from - to 1 mm. in length—and retiring habits render them very inconspicuous, so that as a rule they are overlooked; yet Max Schultze’ asserts that without any doubt they are the most widely distributed of all segmented animals. They are found amongst moss, etc., growing in gutters, on roofs, trees or in ditches, and in such numbers that Schultze states that almost any piece of moss the size of a pea will, if closely examined, yield some members of this group, but they are very difficult to see. The genus Macrobiotus especially affects the roots of moss growing on stones and old walls. JL macronyx lives entirely in fresh water, and Lydella dwjardini and Echiniscoides sigismundi are marine; all other species are practically terrestrial, though in- habiting very damp places. In searching amongst the heather of the Scotch moors for the ova and embryos of the Nematodes which infest the ali- mentary canal of the grouse, I have recently adopted a method not, as far as I am aware, in use before, and one which in every 1 Arch. mikr. Anat. Bd. i., 1865, p. 428. 477 478 TARDIGRADA CHAP, case has yielded a good supply of Tardigrades otherwise so difficult to find. The method is to soak the heather in water for some hours and then thoroughly shake it, or to shake it gently in a rocking machine for some hours. The sediment is allowed to settle, and is then removed with a pipette and placed in a centrifugaliser. A few turns of the handle are sufficient to Fie. 250.—Cast-off cuticle of Macrobiotus tetradactylus, Gr., x about 150, contain- Fia. 249. —Dorsal view of Echiniscus ing four eggs in which the testudo, C. Sch., x 200, showing the boring apparatus of the em- four segments 1, 2, 3, 4. (From bryo can be distinguished. Doyere.) (From R. Greeff. ) concentrate at the bottom of the test-tubes a perfectly amazing amount of cryptozoic animal life, and amongst other forms I have never failed to find Tardigrades. Many Tardigrades are very transparent; their cells are large, and arranged in a beautifully symmetrical manner; and since those of them that live in moss, and at times undergo desiccation, are readily thrown into a perfectly motionless state, during which they may be examined at leisure, it is not sur- prising that these little creatures have been a favourite object XIX ANATOMY 479 for histological research. One way to produce the above-men- tioned stillness is partly to asphyxiate the animals by placing them in water which has keen boiled, and covering the surface of the water with a film of oil. The whole body is enclosed in a thin transparent cuticle, which must be pierced by a needle if it be desired to stain the tissues of the interior. As a rule the cuticle is of the same thickness all over the body, but im the genus Echiniscus the cuticle of the dorsal surface is arranged in thickened plates, and these plates are finely granulated. From time to time the 7 : G Fic. 251.—Zchintscus spinulosus, C. Sch., x about cuticle is cast, and this 200, seen from the side. (From Doyére.) is a lengthy process, so that it is not unusual to find a Tardigrade ensheathed in two cuticles, the outer of which is being rubbed off. The Macro- bioti lay their eggs in their cast cuticle (Fig. 250). The end of each of the eight legs bears forked claws of cuticular origin. The legs are not jointed except in the genus Lydella, where two divisions are apparent. Within the cuticle is the epidermis, a single layer of cells arranged in regular longitudinal and transverse rows along the upper and under surface, where the cells are as uniformly arranged and as rectangular as bricks. The cells on the sides of the body are polygonal, and not in such definite rows. The nuclei show the same diagrammatic symmetry as the cells which con- tain them, and lie in the same relative position in neighbouring cells. In a few places, such as the end of each limb and around the mouth and arms, the cells of the epidermis are heaped up and form a clump or ridge. In some genera a deposit of pig- ment in the epidermis, which increases as the animal grows old, obscures the internal structures. It is generally brown, black, or red in colour. The cuticle and epidermis enclose a space in which the various internal organs lie. This space is traversed by numerous symmetrically disposed muscle-fibres, and contains a clear fluid— the blood—which everywhere bathes these organs. This fluid Sie =" 480 TARDIGRADA CHAP. evaporates when desiccation takes place, and is soon replaced after rain; it forms no coagulum when reagents are added to it, and it probably differs but little from water. Float- ing in it are numerous corpuscles, whose number increases with age. In well-fed Tardigrades the corpuscles are packed with food-reserves, often of the same colour—green or brown—as the con- tents of the stomach, which soon disappear when the little creatures are starved. The alimentary canal begins with an oral cavity, which is in many species surrounded by chitinous rings. The number of these rings and _ their general arrangement are of systematic importance. The oral cavity opens behind into a fine tube lined with chitin, very characteristic of the Tardigrada, which has been termed the mouth- Fic. 252.— Macrobiotus schultzei, Gr., x 150. tube. By its side, eon- (Modified from Greeff.) a, The six inner papillae of the mouth; #, the chitin-lined oesophagus; VETSINg anteriorly, he the c, calcareous spicule; d, muscle which moves two echitinous teeth, which the spicule; e, muscular pharynx with masti- a cating plates; f, salivary glands; g, stomach; May Open ventrally into h, ovary; 7, median dorsal accessory gland ; the mouth-tube, as in > k, diverticula of rectum. Maneater hufelandi and Doyeria simplex, or may open directly into the oral cavity, as in Hehiniscus, Milnesiwm, and some species of Macrobiotus. In some of the last named the tips of the teeth are hardened by a calcareous deposit. The hinder end of each stylet or tooth is XIx ANATOMY 481 supported by a second chitinous tooth-bearer,’ and the movement of each is controlled by three muscles, one of which, running forwards to the mouth, helps to protrude the tooth, whilst the other two running upwards and downwards to the sheath of the pharynx, direct in what plane the tooth shall be moved. The mouth-tube passes suddenly into the muscular sucking pharynx, which is pierced by a continuation of its chitinous tube. Roughly speaking, the pharynx is spherical ; the great thickness of its walls is due to radially arranged muscles which run from the chitinous tube to a surrounding membrane. When the muscles cortract, the lumen of the tube is enlarged, and food, for the most part liquid, is sucked in. Two large ‘glands, composed of cells with conspicuous nuclei, but with ill-defined cell out- lines, pour their contents into the mouth in close proximity to the exit of the teeth. The secretion of the glands—often termed salivary glands—is said in many cases to be poisonous. The pharynx may be followed by a distinct oesophagus, or it may pass alinost immediately into the stomach, which con- sists of a layer of six-sided cells arranged in very definite rows. In fully-fed specimens these cells project into the lumen with a well-rounded contour. Posteriorly the stomach contracts and passes into the narrow rectum, which receives anteriorly the products of the excretory canals and the reproductive organs, and thus forms a cloaca. Its transversely-placed orifice les between the last pair of legs. The food of Tardigrades is mainly the sap of mosses and other humble plants, the cell-walls of which are pierced by the teeth of the little creatures. The organs to which an excretory function has been attributed are a pair of lateral caeca, which vary much in size according as the possessor is well or ill nourished. They recall the Malpighian tubules of such Mites as Tyroglyphus. Nothing comparable in structure to nephridia or to coxal glands has been found. The muscles show a beautiful symmetry. There are ventral, dorsal, and lateral bundles, and others that move the limbs and teeth, but the reader must be referred to the works of Basse, Doyére,” and Plate® for the details of their arrangement. The muscle-fibres are smooth. 1 A. Basse, Zeitschr. wiss. Zool. \xxx., 1906, p. 259. 2 Ann. Sct. nat. (2), xiv., 1840, p. 269, and xvii., 1842, p. 193. ® Zool. Jahrb. Anat. iii., 1889. This paper contains a bibliography. VOL. IV 21 482 TARDIGRADA CHAP, The nervous system consists of a brain cr supra-oesophageal ganglion, whose structure was first elucidated by Plate, and a ventral chain of four ganglia. Anteriorly the brain is rounded, PE fee and gives off a nerve to the skin ; 7 === posteriorly each half divides into ' two lobes, an inner and an outer. The latter bears the eye-spot when this is present. Just below this eye a slender nerve passes straight to the first ventral ganglion. The brain is continued round the oral cavity as a thick nerve-ring, the ventral part of which forms the Fic. 253.—Brain of Macrobiotus hufel- sub-oesophageal ganglion, united andi, C. Sch., x about 850. (From by two longitudinal commissures Plate.) Seen from the side. ap, Lobe Z of brain bearing the eye; ce, supra- tO the first ventral ganglion. oesophageal ganglion; d, tooth; Ga, Thus the brain has two channels first ventral ganglion ; ga’, sub-oeso- : f : phageal ganglion ; &, thickening of the Of Communication between it and epidermis round the mouth ; oc, eye- the ventral nerve-cord on each spot ; 0e, oesophagus ; op, nerve run- ning from the ocular lobe of the brain side, one by means of the slender ee ie ventral ganglion; ph, nerve above mentioned, and one through the — sub - oesophageal ganglion. The ventral chain is composed of four ganglia con- nected together by widely divaricated commissures. Each ganglion gives off three pairs of nerves, two to the ventral mus- culature, and one to the dorsal. The terminations of these nerves in the muscles are very clearly seen in these transparent little creatures, though there is still much dispute as to their exact nature. The older writers considered the Tardigrada as hermaphrodites, but Plate and others have conclusively shown that they are bisexual, at any rate in the genus JJacrobiotus. The males are, however, much rarer than the females. The reproductive organs of both sexes are alike. Both ovary and testis are unpaired structures opening into the intestine, and each is provided with a dorsal accessory gland placed near its orifice. In the ovary many of the eggs are not destined to be fertilised, but serve as nourishment for the more successful ova which survive. No special circulatory or respiratory organs exist, and, as in many other simple organisms, there is no connective tissue. xIX DEVELOPMENT—AFFINITIES 483 The segmentation of the egg in JZ macronyx is total and equal, according to the observations of von Erlanger.' A blastula, followed by a gastrula, is formed. The blastopore closes, but later the anus appears at the same spot. There are four pairs of mesodermic diverticula which give rise to the coelom and the chief muscles. The reproductive organs arise as an unpaired diverticulum of the alimentary canal, which also gives origin to the Malpighian tubules. The development is thus very primi- tive and simple, and affords no evidence of degeneration. With regard to their position in the animal kingdom, writers on the Tardigrada are by no : xe Fig. 254.—Male reproductive organs of means agreed. OL EF. Muller Macrobiotus hufelandi, C. Sch., x placed them with the Mites ; about 350, (From Plate. ) a.ep, Epi- ‘ dermal thickening round anus; ¢/, Schultze and Ehrenberg near the cloaca; gi.d, accessory gland; gi./, Crustacea ; Dujardin and Doyeére We Sue gland ; a SuOnE te, is f testis ; 2, mother-cells of spermatozoa. with the Rotifers near the Annelids; and yon Graff with the Myzostomidae and the Pentastomida. Plate regards them as the lowest of all air- breathing Arthropods, but he carefully guards himself against the view that they retain the structure of the original Tracheates from which later forms have been derived. He looks upon Tardigrades as a side twig of the-great Tracheate branch, but a twig which arises nearer the base of the branch than any other existing forms. These animals seem certainly to belong to the Arthropod phylum, inasmuch as they are segmented, have feet ending in claws, Malpighian tubules, and an entire absence of cilia. The second and third of these features indicate a relationship with the Tracheate groups; on the other hand there is an absence of paired sensory appendages, and of mouth-parts. Von Erlanger has pointed out that the Mal- pighian tubules, arising as they do from the mid-gut, are not homologous with the Malpighian tubules of most Tracheates, 1 Morph. Jahrb. xxii., 1895, p. 491. 484 TARDIGRADA CHAP. and he is inclined to place this group at the base or near the base of the whole Arthropod phylum. They, however, show little resemblance to any of the more primitive Crustacea. The matter must remain to a large extent a matter of opinion, but there can be no doubt that the Tardigrades show more marked affinities to the Arthropods than to any other group of the animal kingdom. Biology.—Spallanzani, who published in the year 1776 his Opuscules de physique animale et végétale, was the first satisfactorily to describe the phenomena of the desiccation of Tardigrades, though the subject of the desiccation of Rotifers, Nematodes, and Infusoria had attracted much notice, since Leeuwenhoek had first drawn attention to it at the very beginning of the century. In its natural state and in a damp atmosphere Tardigrades live and move and have their being like other animals, but if the surroundings dry up, or if one be isolated on a microscopic slide and slowly allowed to dry, its movements cease, its body shrinks, its skin becomes wrinkled, and at length it takes on the appearance of a much weathered grain of sand in which no parts are distinguishable. In this state, in which it may remain for years, its only vital action must be respiration, and this must be reduced to a minimum. When water is added it slowly revives, the body swells, fills out, the legs project, and gradually it assumes its former plump appearance. For a time it remains still, and is then in a very favourable condition for observation, but soon it begins to move and resumes its ordinary life which has been so curiously interrupted. All Tardigrades have not this peculiar power of revivification ——anabiosis, Preyer calls it—it is confined to those species which live amongst moss, and the process of desiccation must be slow and, according to Lance,’ the animal must be protected as much as possible from direct contact with the air. According to Plate, the Tardigrada are free from parasitic Metazoa, which indeed could hardly find room in their minute bodies. They are, however, freely attacked by Bacteria and other lowly vegetable organisms, and these seem to flourish in the blood without apparently producing any deleterious effects on the host. Plate also records the occurrence of certain enigmatical spherical bodies which were found in the blood or more usually in the cells 1 ¢. R. Ae} Sci. cxviii., 1894, p. 817. XIX SYSTEMATIC 485 of the stomach. These bodies generally appeared when the Tardigrades were kept in the same unchanged water for some weeks. Nothing certain is known as to their nature or origin. Systematic.—A good deal of work has recently been done by Mr. James Murray on the Polar Tardigrades and on the Tardigrades of Scotland, many of which have been collected by the staff of the Lake Survey.’ Over forty species have been deseribed from North Britain. The following table of Classification is based on that drawn up by Plate :— Table of Genera. I. The claws of the legs are simple, without a second hook. If there are several on the same foot they are alike in structure and size. A. The legs are short and broad, each with at least two claws. 2-4 claws... . Gen. 1. ECHINISCUS, C. Sou. (Fig. 249). 7-9 claws. . Sub-gen. la. HCHINISCOIDES, Prater. B. The legs are long and slender ; each bears only one small claw. Gen. 2: LY DELLA, Doy. Il. The claws of the legs are all or partly two- or three-hooked. Frequently they are of different lengths. A. There are no processes or palps around the mouth. I. The muscular sucking pharynx follows closely on the mouth- tube. a. The oral armature consists on each side of a stout tooth and a transversely placed support. Gen. 3. MACROBIOTUS, C. Scu. (Fig. 252). f. The oral armature consists on each side of a stylet-like tooth without support. Gen. 4. DOYERIA, PiarE. II. The mouth- tube is separated from the muscular sucking pharynx by a short oesophagus. Gen. 5. DIPHASOON, Puate (Fig. 255). B. Six short processes or palps surround the mouth, and two others are placed a little farther back. Gen. 6. MILNESIUM, Doy. 1. Genus ECHINISCUS (= EURYDIUM, Dovy.).— The dorsal cuticle is thick, and divided into a varying number of shields, which bear thread- or spike-like projections. The anterior end forms a proboscis-like extension of the body. Two red eye-spots. There are many species, and the number has increased so rapidly in the last few years that specialists are talking of splitting up the 1 Tr. R. Soc. Edinb. xlv., 1908, p. 641. This contains a Bibliography of recent literature. See also Richters, Zool. Anz. xxx., 1906, p. 125, and Heinis, Zool. Anz. XXXilil., 1908, p. 69. 486 TARDIGRADA CHAP. genus. J. arctomys, Ehrb.; 2. mutabilis, Murray ; £. islandicus, Richters ; #. gladiator, Murray; #. wendti, Richters; L. reticulatus, Murray; £. othonnae, Richters; £. granulatus, Doy.; E. spitzber- gensis, Scourfield ;! H. guadrispinosus, Richters; and £. muscicola, Plate, are all British. More than one-half of these species are : also Arctic, and £. arctomys is in addition Antarctic. In fact, the group is’a very cosmopolitan one. The genus is also widely distributed vertically, specimens being found in cities on the sea level and on mountains up to a height of over 11,000 feet. la. Sub-genus HCHINISCOIDES differs from the preceding in the num- ber of the claws, the want of definition in the dorsal plates, and in being marine. The single species /. sigismundi, M. Sch., is found amongst algae in the North Sea (Ostend and Heligoland). 2. Genus LYDELLA’?—tThe long, thin legs of this genus have two seg- ments, and in other respects approach the Arthropod limb. Marine. Plate suggests the name L. dujardini for the single species known. 3. Genus MACROBIOTUS has a aE ae Ae pigmented epidermis, but eye-spots may Plate.) ce, Brain ; &, thicken- be present or absent. The eggs are laid ie aa Sc renaEN moe one at a time, or many leave the body phagus ; p, ‘salivary glands; at once. They are either quite free ph, pharynx ; sa, blood cor- . . puscles ; st, stomach. or enclosed in a cast-off cuticle. The genus is divided into many species and shows signs of disruption. They mostly live amongst moss ; but JL macronyx, Doy., is said to live in fresh water. The following species are recorded from North Britain: J/. ober- hdusert, Doy.; M. hufelandi, Schultze; M. zetlandicus, Murray ; M. intermedius, Plate; M. angusti, Murray; M. annulatus, Murray; 1 P. Zool. Soc. 1897, p. 790. ° Hay, in P. Biol. Soc. Washington, xix., 1906, p. 46, states that the name Lydella, Dujardin, is preoccupied, and suggests as a substitute Mierolyda. XIX SYSTEMATIC 487. M. tuberculatus, Plate; IM. sattleri, Richters ; IL. papillifer, Murray: M. coronifer, Richters ; MZ crenulatus, Richters; M. harmsworthi, Murray; JL orcadensis, Murray; I. islandicus, Richters ; JL. dispar, Murray ; JL ambiguus, Murray ; I pullari, Murray ; MW. hastatus, Murray; JZ dubius, Murray; JL. echinogenitus, Richters ; IL. ornatus, Richters ; J. macronyx ? Doy. 4. Genus DOYERIA-——The teeth of this genus have no support, and the large salivary glands of the foregoing genus are absent; in other respects Doyeria, with the single species Doyeria simplex, Plate, resembles Macrobiotus, and is usually to be found in consort with JZ hufelandi, C. Sch. 5. Genus DIPHASCON resembles JI. oberhduseri, Doy., but an oesophagus separates the mouth-tube from the sucking pharynx, and the oral armature is weak. The following species are British, the first named being very cosmopohtan, being found at both Poles, in Chili, Europe, and Asia: D. chilenense, Plate ; D. scoticum, Murray; D. bullatum, Murray; D. angustatum, Murray; D. oculatum, Murray, D. alpinum, Murray ; D. spitz- bergense, Murray. 6. Genus MJZLNEHSIUM has a soft oral armature, and the teeth open straight into the mouth. A lens can usually be distinguished in the eyes. Two species have been described, M. tardigradum, Doy., British, and IZ. alpigenum, Ehrb. Bruce and Richters consider that these two species are identical. CHAPTERAXX PENTASTOMIDA ! OCCURRENCE—-ECONOMIC IMPORTANCE—-STRUCTURE— DEVELOPMENT AND LIFE-HISTORY—SYSTEMATIC PENTASTOMIDS are unpleasant-looking, fluke-lke or worm-like animals, which pass their adult lives in the nasal cavities, frontal sinuses, and lungs of flesh-eating animals, such as the Carnivora, Crocodiles, and Snakes; more rarely in Lizards, Birds, or Fishes. From these retreats their eggs or larvae are sneezed out or coughed up, or in some other way expelled from the body of their primary host, and then if they are eaten, as they may well be if they fall on grass, by some vegetable-feeding or omnivorous animal, they undergo a further development. If uneaten the eggs die. When once in the stomach of the second host, the egg-shell is dissolved and a larva emerges (Fig. 260, p. 494), which bores through the stomach-wall and comes to rest in a cyst in some of the neighbouring viscera. Here, with occasional wanderings which may prove fatal to the host, it matures, and should the second host be eaten by one of the first, the encysted form escapes, makes its way to the nasal chambers or lungs, and attaching itself by means of its two pairs of hooks, comes to rest on some surface capable of affording nutriment. Having once taken up its position the female seldom moves, but the males, 1 The animals included in this group are usually called Linguatulidae or Pentastomidae after the two genera or sub-genera Linguatula and Pentastoma. But the animal which Rudolphi in 1819 (Synopsis Hntozoorwm) named Pentastoma had been described, figured, and named Porocephalus by Humboldt (Recueil d@ observations de zoologie et anatomie comparee, i. p. 298, pl. xxvi.) in 1811. The familiar name Pentastoma may, however, be preserved by incorporating it in the designation of the group. 488 CHAP, XX LIFE-HISTORY AND STRUCTURE 489 which are smaller than the females, are more active. They move about in search of a mate. Further, should the host die, both sexes, after the manner of parasites, attempt to leave the body. Like most animals who live entirely in the dark they develop no pigment, and have a whitish, blanched appearance. The only species of Pentastomid which has any economic importance is Linguatula taenioides of Lamarck, which is found in the nose of the dog, and much more rarely in the same position in the horse, mule, goat, sheep, and man. It is a com- paratively rare parasite, but occurred in about 10 per cent of the 630 dogs in which it was sought at the laboratory of Alfort, near Paris, and in 5 out of 60 dogs examined at Toulouse. The symptoms caused by the presence of these parasites are not usually very severe, though cases have been recorded where they have caused asphyxia. The larval stages occur in the rabbit, sheep, ox, deer, guinea-pig, hare, rat, horse, camel, and man, and by their wandering through the tissues may set up peritonitis and other troubles. As in the Cestoda, which they so closely resemble in their life-history, the nomenclature of the Pentastomids has been com- plicated by their double life. For long the larval form of Z. taenioides was known by different names in different hosts, e.g. Pentastoma denticulatum, Rud., when found in the goat, P. serratum, Frohlich, when found in the hare, P. emarginatum when found in the guinea-pig, and so on. In the systematic section of this article some of the species mentioned are known in the adult state, some in the larval, and in only a few has the life-history been fully worked out. Structure..—-The body of a Pentastomid is usually white, though in the living condition it may be tinged red by the colour of the blood upon which it lives. The anterior end, which bears the mouth and the hooks (Fig. 256), has no rings; this has been termed the cephalothorax. The rest of the body, sometimes called the abdomen, is ringed, and each annulus is divided into an anterior half dotted with the pores of certain epidermal glands and a hinder part of the ring in which these are absent. ~ On the ventral surface of the cephalothorax, in the middle ! This description is mainly based on the account of P. teretiusculus given by Spencer, Quart. J. Micr. Sci. xxxiv., 1893, p. 1. 490 PENTASTOMIDA CHAP. line, lies the mouth, elevated on an oral papilla, and on each side of the mouth are a pair of hooks whose bases are sunk in pits. The hooks can be protruded from the pits, and serve as organs of attachment. Their shape has some systematic value. There are a pair of peculiar papillae which bear the openings of the “ hook-glands,” lying just in front of the pairs of hooks, and other smaller papillae are arranged in pairs on the cephalo- thorax and anterior annul. The entire body is covered by a cuticle which is tucked in at the several orifices. This is secreted by a continuous layer of ectoderm cells. Some of these subeuticular cells are ageregated together to form very definite glands opening through the cuticle by pores which have somewhat unfortunately received the name of stigmata. Spencer attributes to these glands a general excretory function. There is, how- wr ever, a very special pair of glands, Fic. 256. — Porocephalus annulatus, the hook- glands, which extend ae so Ose EO ea almost from one end to the other ; B, ventral view of animal, x 2. of the body; anteriorly these two lateral glands unite and form the head-gland (Fig. 257). From this on each side three ducts pass, one of which opens to the surface on the primary papilla; the other two ducts open at the base of the two hooks which lie on each side of the mouth. Leuckart has suggested that these important glands secrete some fluid like the irritating saliva of a Mosquito which induces an increased flow of blood to the place where it is of use to the parasite. Spencer, however, regards the secretion as having, like the secretion of the so-called salivary cells of the Leech, a retard- ing action on the coagulation of the blood of the host. The muscles of Pentastomids are striated. There is a circular layer within the sub-cuticular cells, and within this a longitudinal XX SHRUG RU RIE 4QI layer and an oblique layer which runs across the body-cavity from the dorso-lateral surface to the mid-ventral line, a primitive arrangement which recalls the similar division of the body-cavity into three chambers in Peripatus and in many Chaetopods. Besides these there are certain muscles which move the hooks and other structures. The mouth opens into a pharynx which runs upwards and then backwards to open into the oesophagus (Fig. 257). Certain muscles attached to these parts enlarge their cavities, and thus give rise to a sucking action by whose force the blood of the host is taken into the alimentary canal. The oesophagus opens by a funnel-shaped valve into the capacious stomach or mid-gut, N AA NSS 7 Fic. 257.—Diagrammatic representation of the alimentary, secretory, nervous, and repro- ductive systems of a male Porocephalus teretiusculus, seen from the side. The nerves are represented by solid black lines. (From W. Baldwin Spencer.) 1, Head-gland; 2, testis; 3, hook-gland ; 4, hind-gut; 5, mid-gut; 6, ejaculatory duct ; 7, vesicula seminalis ; 8, vas deferens ; 9, dilator-rod sac ; 10, cirrus-bulb ; 11, cirrus-sac ; 12, fore-gut ; 13, oral papillae. which stretches through the body to end in a short rectum or hind-gut. The anus is terminal. There appears to be no trace of circulatory or respiratory organs, whilst the function usually exercised by the nephridia or Malpighian tubules or by coxal glands, of removing waste nitrogenous matter, seems, according to Spencer, to be transferred to the skin-glands. The nervous system is aggregated into a large ventral ganglion which lies behind the oesophagus. It gives off a narrow band , devoid of ganglion-cells, which encircles that tube. It also gives off eight nerves supplying various parts, and is continued backward as a ninth pair of prolongations which, running along the ventral surface, reach almost to the end of the body (Fig. 257). The only sense-organs known are certain paired papillae on the head, which is the portion that most closely comes in contact with the tissues of the host. 492 PENTASTOMIDA CHAP. Pentastomids are bisexual. The males are as a rule much less numerous and considerably smaller than the females, although the number of annuli may be greater. The ovary consists of a single tube closed behind. This is supported by a median mesentery. Anteriorly the ovary passes into a right and left oviduct, which, traversing the large hook- gland, encircle the alimentary canal and the two posterior nerves (Fig. 258). They then unite, and at their point of union they receive the ducts of the two spermathecae, usually found packed with spermatozoa. Having received the orifices of the sperma- theca, the united oviducts are continued backward as the uterus, a highly-coiled tube in which the fertilised eggs are stored. These are very numerous; Leuckart estimated that a single female Fia. 258,—Diagrammatic representation of the alimentary, secretory, nervous, and repro- ductive systems of a female Porocephalus teretiusculus, seen from the side. ‘The nerves are represented by solid black lines. (From W. Baldwin Spencer.) 1, Head-gland ; 2, oviduct ; 8, hook-gland; 4, mid-gut; 5, ovary; 6, hind-gut; 7, vagina ; 8, uterus; 9, accessory gland ; 10, spermatheca. may contain half a million eggs. The uterus opens to the exterior in the mid-ventral line a short distance—in P. teretius- culus on the last ring but seven—in front of the terminal anus. In L. taenioides the eggs begin to be laid in the mucus of the nose some six months after the parasite has taken up its position. The testis is a single tube occupying in the male a position similar to that of the ovary in the female. Anteriorly it opens into two vesiculae seminales, which, like the oviducts, pierce the hook-glands and encircle the alimentary canal (Fig. 257). Each vesicula passes into a vas deferens with a cuticular lining. Each vas deferens also receives the orifice of a muscular caecal ejaculatory duct, which, crowded with mature_ spermatozoa, stretches back through the body. Anteriorly the vas deferens passes into a cirrus-bulb, which is joined by a cirrus-sac on one side and a dilator-rod sae on the other, structures containing Xx : LIFE-HISTORY 493 organs that assist in introducing the spermatozoa into the female. The two tubes then unite, and having received a dorsally-placed accessory gland, open to the exterior by a median aperture placed ventrally a little way behind the mouth. Life - history— The egg undergoes a large portion of its development within the body of the mother. In Linguatula taenioides, Which lives in the nasal cavities of the dog, the eggs pass away with the nasal excretions. If these, scattered about in the grass, etc., be eaten by a rabbit, the egg-shell is dissolved in the stomach of the second host and a small larva is set free. In Porocephalus proboscideus and others, which inhabit the lungs of snakes, the eggs pass along the alimentary canal and leave the body with the faeces. They also must be eaten by a second host if development is to proceed. The larva which emerges when the egg-shell is dissolved has a rounded body provided with two pairs of hooked appendages, and a tail which is more or less prominent in different species (Figs. 259, 260). Each ap- pendage bears a_ claw, and is strengthened by a supporting rod or i skeleton. Anteriorly the |\. °°: i EES head bears a boring ap- \[ paratus of several chitin- ous stylets. The various internal organs are in this stage already formed, though in a somewhat °o Pr Ly, oi d : -, Fic. 259.—A late larval stage of Porocephalus pro- rudimentary state, and it boscideus, seen from the side. Highly maguified. is doubtful if the anus (From Stiles.) 1, primordium of first pair of chitinous processes; 2, primordium of second has yet appeared. pair of chitinous processes ; 3, mouth : 4, ventral Fs EE erat eet naga apparatus, and aided by its hooked limbs, the larva now works its way through the stomach-walls of its second host, and comes to rest in the liver or in some other viscus. Its presence in the tissues of its second host causes the formation of a cyst, and within this the larva rests and develops. In man, at least, the cysts often undergo a 494 PENTASTOMIDA CHAP. calcareous degeneration, and Virchow states “dass beim Menschen das Pentastomum am hiufigsten von allen Entozoen zu Verwechse- lungen mit echten Tuberkeln Veranlassungen giebt.” The larva moults several times, and loses its limbs, which seem to have no connexion with the paired hooks in the adult (Fig. 256). The internal organs slowly assume the form they possess m the adult. The larva is at first quite smooth, but as it grows the annula- tions make their ap- pearance, arising in the middle and spreading forward and backward (Fig. 259). In this en- Fic. 260.—Larva of Porocephalus proboscideus, seen from cysted condition the below, Highly maguifed (From Stles) 1, Borg; Jarva, remains coiled seen between the forks of the second pair; 3, ventral up for some months, peas ge are alimentary canal; 5, mouth; ACean dingto Leuckart; six in the case of J. taentoides, and a somewhat shorter period, according to Stiles,! in the case of P. proboscideus. The frequency of what used to be called Pentastoma denti- culatum (=the larval form of LZ. taenioides) in the body of man depends on the famiharity of man with dogs. Klebs and Zaeslin found one larva in 900 and two in 1914 autopsies. Laenger” found the larva fifteen times in about 400 dissections, once in the mesentery, seven times in the liver, and seven times in the wall of the intestine. After remaining encysted for some time it may 07 6C0, baat B35 v0. 300 0000" 20! 0 6. 1 Zeitschr. wiss. Zool. lii., 1891, p. 85. This contains a very full bibliography, of 143 entries. 2 Centrbl. Bakter. xl., 1906, p. 368; v. also Thiroux, C. R. Soc. Biol. lix., 1905, p. 78. XX SYSTEMATIC AQ5 escape, and begins wandering through the tissues, aided by its hooks and annulations, a proceeding not unaccompanied by danger to its host. Should the latter be eaten by some carnivorous animal, the larva makes its way into the nasal cavities or sinuses, or into the lungs of the flesh-eating creature, and there after another ecdysis 1t becomes adult. If, however, the second host eseapes this fate, the larvae re-encyst them- selves, and then if swallowed they are said to Fra. 261.—Eneysted bore through the intestine of the flesh-eater, and — form of —Poro- so make their way to their adult abode. ee a Systematic.'—The Pentastomida are a group mesentery of its much modified by parasitism, which has so deeply ie ees moulded their structure as to obscure to a great extent their origin and affinities. The larva, with its clawed limbs, recalls the Tardigrades and certain Mites, e.g. Phytoptus, where only two pairs of limbs persist, and where the abdomen is elongated and forms a large proportion of the body. The resemblances to a single and somewhat aberrant genus must not, however, be pressed too far. The striated muscles, the ring-like nature of the reproductive organs and their ducts, perhaps even the disproportion both in size and number of the females to the males, are also characters common to many Arachnids. The Pentastomida include three genera, Linguatula, Frohlich, Porocephalus, Humboldt, and Reighardia, Ward.” The first two were regarded by Leuckart as but sub-genera, but Railliet * and Hoyle* have raised them to the rank of genera. They are characterised as follows :— Linguatula, body flattened, but dorsal surface arched ; the edges of the fluke-like body crenelated; the body-cavity extends as diverticula into the edges of the body. Porocephalus, body cylindrical, with no diverticula of the body- cavity. Reighardia, devoid of annulations, transparent, with poorly developed hooks and+a mouth-armature. _ 1 Shipley, Arch. parasit. i., 1898, p. 52. This contains lists of synonyms and of memoirs published since Stiles’ paper, etc. 2H. B. Ward, P. Amer. Ass. 1899, p. 254. 3 Nouv. Dict. de méd., de chir. et Vhyg. vétérinaires, xii. 1883. 4 Tr, R. Soc. Edinb. xxxii., 1884, p. 165. 496 PENTASTOMIDA . CHAP. The following is a list of the species with their primary and secondary or larval hosts :— i. Linguatula pusilla, Diesing, found in the intestine of the fresh-water fish Acara, a South American genus of the Cichlidae. This is possibly the immature form of L. subtriquetra. ii. L. recurvata, Diesing, found in the frontal sinuses and the trachea of Felis onca. ili. L. subtriquetra, Diesing, found in the throat of Caiman latirostris and C. sclerops, perhaps the mature form of L. pusilla. iv. L. taentoides, Lamarck, found in the frontal sinuses and nasal chambers of the dog and ounce, and in the nasal cavities of the wolf, fox, goat, horse, mule, sheep, and man, and in the trachea of the ounce. The immature form has been found in or on the liver of the cat, guinea- pig, and horse; in the lungs of the ox, cat, guinea-pig, porcupine, hare, and rabbit; in the liver and connective tissue of the small intestine of man; and in the mesenteric glands of the ox, camel, goat, sheep, antelope, fallow-deer, and mouse. v. Porocephalus annulatus, Baird, found in the lungs of the Egyptian cobra, Naja haje ; the immature form is thought to live encapsuled in a species of Porphyrio! and in the Numidian Crane. vi. P. aonycis, Macalister, from the lungs of an Indian otter taken in the Indus. vii. P. armillatus, Wyman, found in the adult state in the lungs of certain African pythons, and in the lion; in the larval form it occurs encysted in the abdomen of the Aard-wolf, the mandril, and man— usually in negroes. Its migrations in the body of its second host sometimes cause fatal results. bifurcatus, Diesing, found in the body-cavity of certain snakes, and in the lungs of boa-constrictors and the legless lizard, Amphisbaena alba. Possibly an immature form. ix. P. clavatus, Lohrmann, found in the lungs of the Monitor lizard. x. P.crocidura, Parona, found in the peritoneum of the “ musk-rat ” Oroez- dura in Burmah. Probably a larval form. xi. P. crotali, Humboldt, found in the lungs, body-cavity, kidneys, spleen, and mesentery of many snakes and lizards, and of the lion and leopard. The immature forms occur in the liver and abdominal cavity of species of opossum, armadillo, mouse, raccoon, bat, and marmoset. xii. P. geckonis, Dujardin, found in the lungs of a Siamese gecko. xiii. P. gracilis, Diesing, found free in the body-cavity or encapsuled on the viscera and mesenteries of South American fishes, snakes, and lizards. xiv. P. heterodontis, Leuckart, found encapsuled in the abdominal muscles and mesentery of a species of Heterodon. xv. P. indicus,? vy. Linst., found in the trachea and lungs of Gavialis gangeticus. xvi. P. lari, Mégnin, found in the air-sacs of the Burgomaster or Glaucous gull, Larus glaucus of the Polar seas. Y Ville. 1 Lohrmann, Arch. Naturg. Jahrg. 55, i., 1889, p. 303. * Von Linstow, J. &. Asiat. Soc. Bengal, ii., 1906, p. 270. = SYSTEMATIC 497 xvii. P. megacephalus, Baird, found embedded in the flesh of the head of an Indian crocodile, C. palustris, the “ Mugger.” Probably a larval form. xviii. P. megastomus, Diesing, found in the lungs of a fresh-water tortoise, Hydraspis geoffroyana. xix, P. moniliformis, Diesing, found in the lungs of pythons. xx. P. najae sputatricis, Leuckart, found encapsuled in the abdominal muscles and peritoneum of the cobra, Naja tripudians. Probably a larval form. xxi. P. oxycephalus, Diesing, found in the lungs of crocodiles and alligators. xxl. P. platycephalus, Lohrmann, habitat unknown. xxii. P. subuliferus, Leuckart, in the lungs of the cobra Naja haje. xxiv. P. teretiusculus, Baird, found in the lungs and mouth of certain Australian snakes. xxv. P. tortus, Shipley, found in the body-cavity of a snake, Dipsadomorphus trreguiaris, taken in New Britain. . Reighardia, sp., Ward, found in the air-sacs of Bonaparte’s gull and the common North American tern. XXV I VOL. IV 2K PYCNOGONIDA BY D’ARCY W. THOMPSON, C.B., M.A. Trinity COLLEGE Professor of Natural History in University College, Dundee CHAP TER XSL 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- tonales, strom, ar 62): 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, ‘¢ Fic. 262.—Pycnogonum littorale, Strom, x 2. 1 Pyenogonides, 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, limbless, 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 animal 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, Séndm. '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 ; Oculi iv. dorsales, a, in gibbositate thoracis positi ; c, Antennae 2 tubo breviores moniliformes, subtus in segmento thoracis, cui ocull insident, radicatae ; segmenta corporis, excepto tubo, iv., cum tuberculo e medio singuli segmenti prominulo. Pedes viii., singuli ex articulis vii. XX! GENERAL STRUCTURE 503 The common Pyenogonum 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- rellae with skeleton limbs to the branches of Zoophytes, where their slender forms are not easily seen. In contrast to the stouter body and limbs of Pycnogonum, the whole : fabric of Nymphon a A ey tends to elongation ; 4 Wy the body is drawn out Oat so that the successive ¢ ibe lateral processes stand ee NOS far apart, and a slender a A neck intervenes — be- tween the oculiferous // [| tubercle and the pro- "= ss boscis; the legs are produced to an amazing length and an extreme i ; degree of attenuation : i “mirum tam parvum — corpus regere tam ——v magnos pedes,” Says Fic. 263.—Dorsal view of Nymphon brevirostre, Hodge, x 6. Britain. Linnaeus. Above the 4 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-like 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 Pycnogonwm seems to have arisen with Job Baster, 1765 ; cf. Stebbing, A7iow- ledge, February 1902, and Challenger Reports, ‘* Amphipods,” 1888, pp. 28, 30, etc. 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 Pycnogonwm, 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 Pycnogon, save these, exhibits a greater number of appendages than Mymphon nor a less number than Pycnogonum, nor are any other conspicuous organs to be discovered in other genera that are not represented in these two: within so narrow limits le 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 Wymphon 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 apres eet Sk by denominating the appendages by below, showing chelo- simple numbers, 1 ie EE Vier AAU KS ee palps, and oviger- ond 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 XXI BODY AND LIMBS 505 or “chelophkores,” 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 Pycnogonum, still more attenuated than in Nymphon. In a few forms (eg. Pallene, Ammothea, Tanystylum, Colos- sendeis) the last two, or even more, segments of the trunk are A B Cc Fic. 265.—A, Colossendeis proboscidea, Sabine, Britain ; B, Aimmothea echinata, Hodge, Britain ; C, Phoxichilus 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, Phowichilus, 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 Yanystylum and Fic. 266.—A, B, Chelophores of Ascorhynchus abyssi, G.O.S. A, Young; B, adult. (After Sars.) .C, Anterior portion of Animothea 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 Eurycide, Ascorhynchus, and Barana they are usually less atrophied, but yet comparatively small and with imperfect chelae, while in some Ascorhynchi (A. 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, Fic. 267.—Chelae of species of Nymphonidae: A, Mymphon brevirostre, Hodge; B, Boreonymphon robustum, Bell; C, Chaetonymphon macronyz, 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.” GL CHELOPHORES, PALPI, Eric. 507 these the terminal portion or “hand” forms a ae ? ae of which the ultimate joint forms the “movable finger.” In some species of Mymphon 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 vrobustum the claws are greatly curved, with a wide gape between. In this last, and in Phoawichilidium, the oppos- ing edges are smooth and toothless. In Cordy- Pia. 268. — Proboscis lochele the hand is almost globular, the movable 224 _chelophores of Cordylochele longt- 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 Pycnogonum, Phouxichilus, Phoxi- chilidium, Pallene, and their allies. In certain of these cases, e.g. 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 Fie. 269.—Eury- the number of joints ranges from five or six 10 ee ae Tanystylum to nine (as a rule) in Ammothea and stalked pro- Oorhynchus, or ten, according to Dohrn, in certain ee “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 niles that they perform the function which the name connotes." They 1 As a rare exception, Hoek has found the eggs carried on the ovigerous legs in a single female of Nymphon brevicaudatum, Miers. 508 PYCNOGONIDA 17 CHARS 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 ail the rest os | ( A on Fra. 270.—Ovigerous legs of A, Phoxichilus spinosus, Mont. ; B, Phoxichilidium femor- atum, Rathke; C, Anoplodactylus petiolatus, Kr.; D, Colossendets proboscideus, Sab. 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, Fic. 271.— Terminal joints of oviger- Phoxichilus seven ; in Paranymphon ous leg of Rhynchothorax medi- _- shou ra veins : itl fonraneee Cue: eight; in Pycnogonwm nine, with, in addition, a terminal claw; in the Ammotheidae 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 Fis. 272. — Nymphon ; : brevirostre, Hodge. takes the form of a stout toothed tubercle Terminal joints of on each joint; in Colossendeis of several ovigerous leg, with y ; : i" 2 magnified “ tooth. 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 Og 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 Vymphon and \ \ Fic. 273.—Nymphon strémii, Kr. Male carrying egg-masses on his ovigerous legs. © I} o 5 D fo} Colossendeis, the fourth, fifth, and sixth joints 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, NV. 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 » SCHAR: Fic. 275.—Legs of A, Padlene brevirostris, Johuston ; B, Anoplodactylus petiolatus, Kr. ; C, Phowxichilus spinosus, Mont. ; D, Colossendeis proboscidea, Sabine ; E, Ammothea echinata, Hodge, . auxiliary claws, sometimes large, sometimes small, lie at the base of the terminal claw in Ammotheidae, Phoxichilidae, in Phoxi- XXI GLANDS Sipe chilidiwm, in most Pallenidae, in nearly all Nymphonidae. Their presence or absence is often used as a generic character, helping to separate, e.g., Pallene from Pseudopallene and Pallenopsis, and Phoxichilidium 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. Fie. 276.—Boreonymphon 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 1 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 Pycnogonum the spime 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 See also Hallez, Arch. Zool. Exp. (4), v., 1905, p. 3; Loman, Tijdschr. Ned. Dierk. Ver. (2), x., 1906, p. 271, ete. 8 *©On Hydroid and other Corals,” 1881, p. 78. 524 PYCNOGONIDA ’ CHAP. doubt that they contained the remains of larvae of a Pyenogonid, so that the deep-sea Pycnogonids, which are so abundant, very possibly pass through their early stages in deep-sea Stylasteridae. .. . The gastrozoids containing the larvae were partly aborted.” A Pyenogon larva, doubtfully ascribed to Nymphon, has been found living in abundance ectoparasitically on Zethys in the Bay of Naples.’ Habits.—Of the intimate habits of the Pycnogons we can say little. Pycnogonum we often find clinging, as has been said, close appressed to some large Anemone (7'ealia, Bolocera, etc.), whose living juices it very probably imbibes. The more slender species we find climbing over sea-weeds and Zoophytes, where sometimes similarity of colour as well as delicacy of form helps to conceal them; thus Phowichilidiwm femoratum (Orithyia coccinea, Johnston) is red like the Corallines among which we often find it, P. virescens green like the filamentous Ulvae, the Nymphons yellowish like the Hydrallmania and other Zoophytes which they affect. On the New England coast, according to Cole, the dark purple Anoplodactylus lentus, Wilson (Phoaichilidium maaxillare, Stimpson), is especially abundant on colonies of EHudendrium, whose colour matches its own, the yellowish Tany- stylum orbiculare frequents a certain yellowish Hydroid, and of these two species neither is ever found on the Hydroid affected by the other; while, on the other hand, Pallene brevirostris, whose whitish, almost transparent body is difficult to see, is more generally distributed.” The deep-sea Pyenogons (Colossendeis, Nymphon) are generally (if not universally) of a deep orange- scarlet colour, a common dress of many deep-sea Crustacea. The movements of the Pycnogons are singularly slow and deliberate ; they are manifestly not adapted to capture or to kill a living prey. Linnaeus accepted from J. C. Konig the singular statement that they enter and feed upon bivalve shells, “ Myti- lorum testes penetrat et exhaurit”’; but the statement has never been reaffirmed. 1 Hugo Mertens, Afitth. Zool. Stat. Neapel, xviii., 1906, pp. 136-141. * One is tempted to explain such cases as the above of harmonious or identical coloration by the simple passage of pigments unchanged from the food. ° Fabricius says of his Pycnogonum (Nymphon) grossipes, ‘‘ Vescitur insectis et vermibus marinis minutis ; quod autem testas inytilorum exhauriat mihi ignotum est, dum nunquam intra testam mytili illud inveni, licet sit verisimile satis,” Fauna Groenlandica, yp. 231. oa HABITS hes Loman describes Phowxichilidium as feeding greedily on Tubularia larynz, and especially on the gonophores. It grasps them with its claws, sucks them in bit by bit till the proboscis is filled as far as the sieve, whereupon that part of the proboscis squeezes and kneads the mass, letting only juices and fine particles pass through into the alimentary canal. The lateral caeca and the rectum are separated by sphincter muscles from the stomach ; the former are in turn filled with food and again emptied; the contents of the alimentary canal are in constant rolling move- ment, and the faeces -are eliminated by the action of a pair of levatores ani, in round pellets. The Pyenogons, or some of them, can swim by “ treading water,” and Pallene is said by Cole to swim especially well; they more often progress half by swimming, half by kicking on the bottom. They move promptly towards the light, unless they have Hydroids to cling to, and Cole points out that when they crawl with all their legs on the bottom they move forwards towards the light,’ but backwards when they swim in part or whole. The legs move mostly in a vertical plane, horizontal movements taking place chiefly between the first and second joints. Zany- stylum is uncommonly sluggish and inert; it sinks to the bottom, draws its legs over its back and remains quiet, while Pallene, by vigorous kicks, remains suspended. The long legs of the Pycnogons are easily injured or lost, and easily repaired or regenerated. This observation, often repeated, is as old as Fabricius: “ Mutilatur etiam in libertate sua, red- integrandum tamen; vidi enim in quo pedes brevissimi juxta longiores enascentes, velut in asteriis cancris aliisque redinte- gratis.” In such cases of redintegration of a leg, the repro- ductive organ, the genital orifice, and the cement-gland are not restored until the next moult.” Systematic Position-—To bring this little group into closer accord with one or other of the greater groups of Arthropods is a problem seemingly simple but really full of difficulty. The larval Pyenogon, with its three pairs of appendages, resembles the Crustacean Nauplius in no single feature save 1 Loeb (Arch. Entw. Mech. v. 2, 1897, p. 250) also says that the Pyenogons are positively heliotropic. 2 See also P. Gaubert, ‘‘Autotomie chez les Pyenogonides,” Bull. Soc. Zool. Fr. XVii., 1892, p. 224. 526 PYCNOGONIDA te acrim this unimportant numerical coincidence ; nor is there any signifi- cance in the apparent outward resemblance to isolated forms (e.g. Cyamus) that induced some of the older writers, from Fabricius downwards and including Kroyer and the elder Milne-Edwards, to connect the Pycnogons with the Crustacea. To refer them, or to approximate them to the Arachnids, has been a stronger and a more lasting tendency.’ Linnaeus (1767) included the two species of which he was cognisant in the genus Phalangium, together with P. opilio. Lamarck, who first formulated the group Arachnida (1802), let it embrace the Pycnogons; and Latreille (1804, 1810), who immediately followed him, defined more clearly the Pycnogonida as a subdivision of the greater eroup, side by side with the subdivision that corresponds to our modern Arachnida (“ Arachnides aceres”), and together with a medley of lower Crustacea, Myriapoda, Thysanura, and Parasitic Insects; he was so cautious as to add “j’observerai seulement, que je ne connais pas encore bien la place naturelle des Pyeno- gonides et des Parasites,” and Cuvier, setting them in a similar position, adds a similar qualification.” Leach (1814), whose great service it was to dissociate the Edriophthalmata and the Myriapoda from the Latreillian medley, left the group Arachnida as we still have it (save for the inclusion of the Dipterous Insect Nycteribia), and divided the group (with the same exception) into four Orders of which the Podosomata, 2.e. the Pycnogonida, are one. Savigny (1816), less philosophical in this case than was his wont, assumed the Crustacean type to pass to the Arachnidan by a loss of several anterior pairs of appen- dages, and appears to set the Pycnogons in an intermediate grade, marking the pathway of the change. He considered the seven pairs of limbs of the Pycnogons to represent thoracic limbs of a Malacostracan, and, like so many of his contemporaries, was much biased by the apparent resemblance of Cyamus to Pycnogonum. The reader may find in Dohrn’s Monograph a guide to many other opinions and judgments, some of them of no small morpho- logical interest and historical value*; but it behoves us to pass 1 Cf. Carpenter, Proc. &. Irish Acad. xxiv., 1903, p. 820; Lankester, Quart. J. Mier, Sei. xlviii., 1904, p. 223; Bouvier, Hap. Antarct. Fr., ‘“‘ Pycnogonides,” 19075 7p. /, ete: 2 “Nous ne les placons ici qu’avec doute,” Regne Anim. éd. 3, tom. vi. p. 298. 3 Of, also J. E. W. Ihle, ‘‘Phylogenie und systematische Stellung der Panto- XXI SYSTEMATIC POSITION Breau them by, and to inspect, in brief, the case as it stands at present. The obvious features in which a Pycnogon resembles a Spider or other typical Arachnid, are the possession of four pairs of walking legs, and the pre-oral position and chelate form of the first pair of appendages; we may perhaps also add, as a more general feature of resemblance, the imperfect subservience of limbs to the mouth as compared with any of the Crustacea. The resemblance would still be striking, in spite of the presence of an additional pair of legs in a few Pycnogons, were it not for the presence of the third pair of appendages or ovigerous legs of the Pycnogon, whose intercalation spoils the apparent harmony. We are neither at liberty to suppose, with Claus, that these members, so important in the larva, have been interpolated, as it were, anew in the Pycnogon; nor that they have arisen by subdivision of the second pair, as Schimkewitsch is inclined to suppose; nor that they have dropped out of the series in the Arachnid, whose body presents no trace of them in embryo or adult. In a word, their presence precludes us from assuming a direct homology between the apparently similar limbs of the two groups,’ and at best leaves it only open to us to compare the last legs of the Pycnogon with the first abdominal, or genital, appendages of the Scorpion and the Spider. On the other hand, if we admit the seventh (as we must admit the occasional eighth) pair of appendages of Pycnogons to be unrepresented in the prosoma of the Arachnids, then, in the cephalothorax of the former, with its four pairs of appendages, we may find the homologue of the more or less free and separate part of the cephalothorax in Koenenia, Galeodes, and the Tartaridae. There is a resemblance between the two groups in the presence of intestinal diverticula that run towards or into the limbs, as in Spiders and some Mites, and there are certain histological and embryological resemblances that have been in part referred to above; but these, such as they are, are not adequate guides to morphological classification. We must bear in mind that such resemblances as the Pycnogons poden,” Biol. Centralbl., Bd. xviii., 1898, pp. 603-609 ; Meisenheimer, Verh. zool.- bot. Ges. Wien, xii., 1902, pp. 57-64 ; also Stebbing, in Anowledge, 1902. 1 The chelate form of the foremost appendages is of little moment. A chela consists merely of a more or less mobile terminal joint flexing on a more or less protuberant penultimate one, and in the Scorpions, in Limulus, throughout the -Crustacea, and even in Insects (cf. vol. vi. p. 554), we see such a structure arising independently on very diverse appendages. 528 PYCNOGONIDA ’ CHAP. seem to show are not with the lower Arachnids but with the higher; they are either degenerates from very advanced and specialised Arachnida, or they are lower than the lowest. Con- fronted with such an issue, we cannot but conclude to let the Pycnogons stand apart, an independent group of Arthropods !; and I am inclined to think that they conserve primitive features in the usual presence of generative apertures on several pairs of limbs, and probably also in the non-development of any special respiratory organs. But inasmuch as the weight of evidence goes to show that subservience of limbs to mouth is a primitive Arthropodan character, the fact that the basal elements of the anterior appendages have here (as in Aoenenia) no such relation to the mouth must be taken as evidence, not of antiquity, but of specialisation. In like manner the suctorial proboscis cannot be deemed a primitive character, and the much reduced abdomen also is obviously secondary and not primitive. Classification——No single genus more than another shows signs of affinity with other groups, and no single organ gives us, within the group, a clear picture of advancing stages of com- plexity. On the contrary, the differences between one genus and another depend very much on degrees of degeneration of the anterior appendages, and we have no reason to suppose that these stages of degeneration form a single continuous series, but have rather reason to believe that degeneration has set in independently in various ways and at various points in the series. But while we are unable at present to form a natural classification ® of the Pyenogons, yet at the same time a purely arbitrary or artificial classification, conveniently based on the presence or absence of certain limbs, would run counter to such natural relationships as we can already discern. 1 Cf. Oudemans, Tijdschr. d. Ned. Dierk. Ver. (2), i., 1886, p. 41: ‘*‘ Jedermann weiss nun, dass diese Tiere cine ganz besondere Urgruppe bilden, ohne alle Verwandschaft mit irgend einer anderen Arthropodengruppe.” 2 Cole (Ann. Mag. Nat. Hist. (7), xv., 1905, pp. 405-415) has attempted such a phylogenetic classification, starting with Decolopoda, and leading in two divergent lines, through Nymphon and Pallene to the Pycnogonidae, and through Eurycide and Aimmothea to Colossendeis. This hint is in part adopted in the subjoined classification. Bouvier, in his recent Report on the Pycnogons of the French Antarctic Expedition (¢. cit.), gives reasons for separating the Decolopodidae and Colossendeidae from all the rest. Loman, in Die Pantopoden der Siboga- Expedition, 1908, has recently suggested another, and in many respects novel, classification of the whole group. XXI CLASSIFICATION 529 The classification here adopted is a compromise between a natural system, so far as we can detect it, and an artificial one. Two forms, separated from one another by many differences, show a minimum of degeneration, namely Decolopoda on the one hand, and the Nymphonidae on the other. The former genus has five pairs of legs, and this peculiarity is shared by Penta- nymphon. In both groups the three anterior limbs are all present and well formed, save only that the ovigerous legs, which have ten joints in Decolopoda, are reduced to five joints in the Nymphons, and their denticulate spines, of which several rows are present in the former, are reduced to one row in the latter ; on the other hand, a greater or a less degeneration of these limbs marks each and all of the other families. Decolopoda is very probably the most primitive form known, though it has characters which seem to be the reverse of primitive in the dwarfish size of its chelophores and the crowded coalescent segmentation of the trunk. OColossendeis, in spite of its vanished chelophores, is probably closely allied: the shape and segmentation of the body and the several rows of smooth denticles on the ovigerous legs are points in common. The Eurycydidae are closely allied to Colossendeidae; they agree with Decolopoda in the two-jointed scape of the chelophore, and with Ammotheidae in the deflexed mobile proboscis. The true position of Rhynchothorax is very doubtful. The Nymphonidae and Pallenidae are closely allied, and the Phoxichilidiidae have points of resemblance, especially with the latter. Mymphon compares with Decolopoda in the completeness of its parts, and is more typical in its long well-segmented body, and in its highly-developed chelae; but it already shows reduc- tion in the scape of the chelophore, in the palps, and in the armature of the ovigerous legs. The Phoxichilidae and Pycnogonidae (Agnathonia, Leach ; Achelata, Sars), though differing greatly in aspect, are not im- probably allied to one another; and whether this be so or not, the complete absence of chelophores and of palps affords an arbitrary character by which they are conveniently separated from all the rest. The following table epitomises the chief characters of the several families :— VOL. IV 2M | pesuapuoo IR[NGILL “ F F ‘paquatuseg | Ff ‘Tpeug 26 0 0 se ; WUVAINODONOAT < pe}meutses afd uts poxy 3 7G Gel Poe G EN i “padeqzBog oe, 0 0 ‘osie'] 5 * TVaVIIHOTXoHg f (sueg “eqyepTeqoy) apdcuts se pe oe IE o i ‘MOL 9UQ 9 9-G 0 BE us ‘GT VCIIGITIHOIXOH Arequout a3 } ‘e (Zz cia) (a3 p 6é 4 O19) OL -Ipna Io 0 1G ce . ° WVGINUVIVG poqtoutses A} BL1OS | poqutol: 1 pexy (g) be ‘a ‘Tl (¢) & ‘Eg % TEM G-f ‘mol aug | & ‘P OL-8 (4) ¢ adeos ‘a5ie'T ‘onlery : UVGINOHANAN | -(sdeg “egejeyong) qUBLLIG'e sopotequy ‘poxy a - fp g ii peyqooy, & 2 POT (@) 8 0 ‘anLey WVAIOVUOHLOHONAHY § = Yjoours AZ 10 ayei1as o poquatuses *pa.to} 7808 eo) pexoyep OS ac 2 ‘pesuepuon | Ff eel (SSeT 10) OT 6-F te “O[IQOTW * TVCIMHLONNY ei sourds O ge ue er - peteyy209 SeeMOn 0 Avequemipny Se | ; * pruouunyyr e a R.L108 Area ut pexaypop poqymatuses ‘MOI a0 -Ipna avpato ‘poypRys ator a F ‘eS TT2AN r uvyy etoyy | & ‘P OL OL ‘peqmiol-g adrog) ‘aT Iqoy " WTVdIdINAU AY poeadnoap SaUIT}atUIOS a[duits ‘aTIqour 7 ‘e‘%'‘1 | P ‘eS “TL | Queoseyevog py | ‘smot uvyy | 4 $9 OT OL 0 JBYMEMIOG | * * WVAIMANASSOTO/ | payurol-z quaoseTROo ayduuts & ‘9 adeos ‘|, Rus peaamo G ‘F ‘es ‘% ‘| ‘Go ‘F ‘eg ‘% ‘L| ‘pasuepuog| ¢ ‘smod moj | szutol oT sjutol QT ‘oqatdui0g, -op ‘pexty * avdidodotoord — | —(saieg ‘eqyepeyooyd 19) ° 5 ee Gas ne a = ee ‘s8ary | ‘op uo yAQeaJ, eSUnCENS) ‘sd [nq ‘saaoydojayo ‘stosoqorg | ONDA an ‘ssuruedg [Bye i] | XXI CLASSIFICATION—DECOLOPODIDAE 531 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; IT. 9-10-jointed; IIT. well developed in both sexes, 10-jointed, the terminal joints with 1 See (inter aliw) Dohrn, 7.c. ; E. B. Wilson, Rep. U.S. Fish. Comm. (1878), 1880 ; Hoek, Chall. Report, 1881 ; G. O. Sars, Norw. NV. Atl. Hxp. 1891; Meinert, Zngolf 532 PYCNOGONIDA wCHAP: about four rows of teeth; five pairs of legs, destitute of accessory claws; genital apertures on all the legs (Bouvier). Decolopoda australis, Kights ' (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 trom 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 Kurycididae ; while the Colossendeidae would be very lke 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 II. 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, Fauna 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. &. Phys. Soc. Edinburgh, xvi., 1905, p. 35; Zool. Anz. xxy., 1905, p. 254; Discovery Hup., “*Pyenogonida,” 1907 ; Bouvier, Hap. Antarct. Fr. 1907. 2 See pp. 535, 541. Cf. Dohrn (¢. cit.), p. 228. 3 The first known species was described as Phowichilus proboscideus, Sabine, from the shores of the North Georgian Islands (1821). XXI COLOSSEN DEIDAE—-EURYCIDIDAE 533 in the Southern Ocean, has a span of about two feet. The North Atlantic C. proboscidea and Antarctic C. wustralis are very closely related to one another. Carpenter would retain the genus Rhopalorhynchus for R. kréyeri, W.-M. (Andamans), 2. clavipes, Carp. (Torres Straits), and RL. tenuwissemus, 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 weber, 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. Eurycididae (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, Schiédte (1857) (Zetes, Kroyer, 1845): Appendage I. with two-jointed scape, without chelae in adult ; one species (£4. hispida, (Kr.)), from the North Atlantic and Arctic, and two others from the East Indies, recently described by Loman. Parana 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, 1t should be merged, includes large, smooth, elongated forms, with long neck and Fic. 283.— Hurycide his- pida, Kr. ; side view. expanded frontal region, and a long proboscis lacking the long scape that supports the proboscis in Hurycide; 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 is also, probably, Parazetes auchenicus, Slater, from Japan. Hannonia typica, Hoek (1880), from Cape Town, is a remarkable form, lately redescribed by Loman. The chelophores are much reduced, the palps are absent; the ovigerous legs are 534 PYCNOGONIDA v. GHAB: 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 jcints being provided with the compound spines seen in Nymphon and Pallene. It is perhaps an immature form. Schimkewitsch has described another species, N. korotnevit, and Loman a third, WV. muscosus, both from the East Indies. Fam. 4. Ammotheidae.—Akin to Eurycididae 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 II. 4-9-jointed; appendage III. clawless, and the number of joits sometimes diminished, with a sparse row of serrated spines; auxiliary claws usually present. Ammothea, Leach (1815) (rncluding Achelia, Hodge (1864) = the old non-chelate individuals): appendage I. very small, 2-jointed; appendage IT. 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 Achelia 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 A. achelioides, Wilson; Hndeis didactyla, Philippi (1843), is very probably the same species. A. wniwnguiculata, Dohrn (? Pariboea spinipalpis, Philippi (1843)), 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 ? Pocock (Eneycl. 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 5 transverse ridges on the body, a large proboscis, a 9-jointed palp, and somewhat peculiar ovigerous lees. Cilunculus, Fragilia, and Scipiolus are new genera more or less allied to Leionymphon, described by Loman (1908) from the Siboga Expedition." YZanystylum, Miers (1879) (including Clotenia, Dohrn (1881), and Discoarachne, Hoek (1880)), has append- age I. reduced to a single jomt or a small tubercle, and appendage IJ. 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 JZ. (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, Tanystylum orbiculare, Wilson. Fam. 5. Rhynchothoracidae.—The animal identified by Dohrn as Rhynchothoraz 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-jointed, clawed ovigerous legs, which last are provided on the last five jomts with peculiar toothed tubercles. The general aspect of the body is somewhat like 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). ® Proc. Boston Nat. Hist. Society, vol. i., 1841-44, p. 92. 536 PYCNOGONIDA bee nGrann 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, /. 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, XX1 NYMPHONIDAE—PALLENIDAE 5397 Miers (=. horridum, Bohm), an extraordinary hispid form from Kerguelen,’ is also peculiar. Pentanymphon, Hodgson (1904), from the Antarctic (circumpolar), 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), 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, Australa). P. danguida, Hoek, Australia, lacks auxiliary claws, and is otherwise distinct but P. novaezealandiae, G. M. Thomson, is ty heal Pseudopallene, Wilson (1878):° appendage III. clawed ; auxiliary claws absent; four (or more) species (North Atlantic, Arctic, Antarctic). PP. (Phouichilus) pygmaea, Costa (1836), and P. spinosa, Quatref., seem to belong to this genus or to Pallene. Cordylochele, G.O.Sars (1888): closely alhed, but with front of cephalic segment much expanded and chelae remarkably swollen, includes rahe ose eran three very smooth, elongated, northern species, to — drevirostris, John- which Bouvier has added one from the Antarctic ; ee Bo se 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. 2 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 Phowichilus, Latr., and Phoxichilidae and Phoxichilus, 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 LS CHAR ten species, Hast Indies and Austraha); Pallene grubii, Hoek (Phouxichilidium 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. /ongiceps, 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 III. 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 PHOXICHILIDHDAE—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 Fira. 287.—Anoplodactylus petiolatus, Kr,., Britain. A, Dorsal view; B, side view. Fam. 9. Phoxichilidae.'— Appendave 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. béhmiw, 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 Pyenogonum, Briinnich (1764) (Polygonopus, 1 Vide note 2, p. 537. 540 PYCNOGONIDA ro eHARs Pallas, 1766); the type is P. littorale, Strom, of the N. Atlantic (0-430 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.), 18 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 indispensable advantage of access to Canon Norman’s collection, and the still greater benefit of his own stores of endless information.’ Pseudopallene cireularis, Goodsir: Firth of Forth. Phoxichilidium femoratum, Rathke (P. globoswm, Goodsir; Orithyra coccinea, Johnston) (Figs. 270, B; 286): East and West coasts, Shetland, Ireland. Anoplodactylus virescens, Hodge (? Phoxichilidium olivacewm, 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. 367 ; Ann. Mag. Nat. Hist. (1), xiv., 1844, p. 4. 3 Ann. Mag. Nat. Hist. (3), xiii., 1864, p. 118. 4 Proc. R. Dublin Soc. (N.S.), viii., 1898, p. 195; Fisheries, Ireland, Sei. Invest. 1904, No. iv. (1905). ° Cf. A. M. Norman, J. Zinn. Soc. xxx., 1908, pp. 198-238. XXI THE BRITISH PYCNOGONS 541 A, petiolatus, Kr. (Figs. 270, ¢; 275, B; 287) (Pallene attenuata and pygmaca, Hodge ; Phoaichilidiwm exiguum and longicolle, Dohrn): Plymouth, Firth of Forth, Cumbrae, Irish coasts. Ammothea (Achelia) echinata, Hodge (Fig. 265, B; 274, 4; 275, £): 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. franciscana, 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. muagnirostris, Dohrn, appears to be identical. A. laevis, Hodge: Cornwall (Hodge), Devon (Norman), Jersey (Sinel). Tanystylum orbiculare, Wilson (Clotenia controstre, Dohrn): Donegal (Carpenter). Phoxichilus spinosus, Mont. (Fig. 265, c; 270, A; 275, c): South Coast, Moray Firth, Firth of Clyde, Ireland. A smaller and less spiny form occurs, which Carpenter records as P. laevis, Grube, but Norman unites the two under the name of Endeis spinosus (Mont.). Pycnogonum littorale, Strém (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. strémii, 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 naine 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. minutum, 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. sluiterit, 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 spinosissemum, Norman; Nymphon gracilipes, Heller (non Fabr.); WV. hirtipes, Bell; WV. longitarse, Kr.; WN. 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 XVIT., 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; NV. macronyxz, Sars; NV. 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 Pylopaqgurus, 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 Pentastoinida, 489 ; of Pyenogonida, 502 Abdominal glands, of Chernetidea, 432 Abyssal region (marine), 204 ; (lacustrine), 209 Acantheis, 418 Acanthephyra, 163 Acanthephyridae, 763 Acanthoctenus, 415 Acanthodon, 3888 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, 529 Achelia, 534; A. longipes, 506 Achtheres, 75; A. percarum, 75 Acidaspidae, 257 Acidaspis, 226, 227, 230, 231, 235, 241, 251;