of 1905). Poge ere ing to the family =V]= => a Oo ed wD _ be = wD co pi i (23 ‘ ® 1g ted. States National Museum 5-29 ic copepo Cali C.B. 1905 ican parasiti igidae. Part 1,- The ings of the Uni :473-672, pls. Wilson, North Amer Caligi Proceed 28(1404) Ly me2\NSo Cas SMITHSONIAN INSTITUTION. Fert mone Sak Ae S NA TLOwwN AL. MU SE UyiveE, HY EY C, Poo |. NORTH AMERICAN PARASITIC COPEPODS BELONGING TO THE FAMILY CALIGIDA, Part 1.—THE CALIGINA. BY CHARLES BRANCH WILSON, Way Department of Biology, State Normal School, Westfield, Mass. From the Proceedings of the United States National Museum, Vol. XXVIII, pages 479-672 (with Plates V-X XIX). [No. 1404.] WASHINGTON: GOVERNMENT PRINTING OFFICE. 1905. NORTH AMERICAN PARASITIC COPEPODS BELONGING TO THE FAMILY CALIGID. PART I.—THE CALIGIN/E. By CuHarutes Brancn WILSON, Department of Biology, State Normal School, Westfield, Massachusetts. INTRODUCTION. The present is the third paper in the series based upon the collection belonging to the United States National Museum. The other two papers treated of the Argulidz and were published, the first in Volume XXY, and the second in Volume X XVI of these Proceedings. Acknowledgment was made in them of valuable assist- ance received from various sources, particularly from the United States Bureau of Fisheries. That assistance concerned the present family even more than the Argulide, and the author feels that any success which may have been attained in working out the habits and life histories is due almost entirely to the courtesy and assistance extended by the Bureau of Fisheries. Additional sources of material will be found mentioned under the historical summary (p. 482). This second family, the Caligidz, includes about thirty genera, which separate naturally into groups differing as much in their habits as in their morphology, and thus constituting well-marked divisions. (See Key on p. 532). The genera here treated include all of the first group, the Caligine, which have thus far been found in North American waters, and five species, including one which is the type of a new genus, from foreign localities. The North American species are twenty-three in number, of which thirteen are new, namely: Caligus rujfimaculatus, C. schistony«, C. mutabilis, C. aliuncus, C. chelifer, C. latifrons, C. bonito, Caligodes megacephalus, Lepeophtheirus longipes, L. edwardsi, L. dissimulatus, L. parviventris, L. bifurcatus. Of the five non-American species included in the Museum collection four are new to science, namely, Ca//gus teres, from Lota, Chile; Lepe- ophtheirus innominatus, from Cornwall, England; Lepeophthetrus PROCEEDINGS U. S. NATIONAL MUSEUM, VOL. XXVIII—No. 1404. 479 480 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. XXVIII. chilensis, from Lota, Chile, and Homozotes palliata, the type of a new genus, locality unknown. In addition to these seventeen new species the present paper gives for the first time the development stages of two species, Caligus rapax and (. curtus, almost the entire anatomy of a third, Echetus typicus Kroyer, while it corrects or largely supplements the anatomical details and rectifies the systematic position of seven other species, Caligus pelamydis Kroyer, C. productus Dana, C. thymni Dana, Lepe- ophtheirus thompson? Baird, L. salmonis Kroyer, L. pacificus Gissler, and Caligus centrodonti Baird, the last a non-American species. Here also are presented for the first time a.comparative anatomy of the different species of Caligus and Lepeophtheirus, and artificial keys for the determination of all known species under the several genera. In the development are given for the first time figures of a metanau- plius and the details of its anatomy. And there is introduced the first continuous life history of any species belonging to the family, together with a comparison of the life histories of several species and at least two genera. : This subfamily, the Caligine, is particularly interesting because the genus Caligus, which is the type of the entire family, is one of the oldest among the parasitic copepods and formerly included many species which are now referred to other genera. Among these were some which resembled the true Caligus very closely, except that they lacked the lunules or sucking disks on the frontal plates. From these Van Nordmann created the genus Lepeophtheirus in 1832, but it was not generally accepted at first, and the species of both genera continued to be included under Caligus by many authors up to the appearance of Kroyer’s excellent memoir in 1863. The genus Anuretes also was first placed by Kollar under Caligus in the collection of the Vienna Museum. Like Lepeophtheirus it lacks the lunules on the frontal plates, and hence Kréyer, who was the first to publish a description of the species, classified it as a Lepeophtheirus, and it was not until 1865 that it was established as a distinct genus by Heller. Of the other two genera, one, Caligodes, is simply a Caligus with the free segment elongated into a neck and the genital segment and abdomen modified slightly, while the appendages are identical in the two. The other genus is the new one //omovotes, and differs only in having the genital se2ment covered with « dorsal plate. It has not thus far been found in North American waters, but there is every probability that it will be at some future time. These genera are very closely related to one another therefore, and since both the males and females of all except Caligodes can swim about freely they furnish an excellent group to contrast with the Argulidee on the one side and the Pandarinz on the other. The Argulide are BONEN S. Stag dati have hoe) ; ston (1824), eae (3850), Hi. ‘wand tT. | hd ‘Vist bet ast ae mort Se reelegt tigers Tory is ( onnert 4 4 i RP bw ‘ taal wacila Ht be ORNL 1, dlory, eer degenerate; this group therefore forms a connecting link between | the two and enables us to discover and emphasize the initiatory steps in degeneration. They thus possess the greatest possible ecological interest, and a care- ful study of their habits and mode of life can not fail to yield valuable facts and suggestions. HISTORICAL. The first accounts that can be referred to these genera with any degree of certainty are those of Gunner (1765), Stroem (1762), and Baster (1765). They describe and figure some parasites which they eall fish lice, but evidently they entirely mistook the nature of the ani- mals, since they regarded the egg strings as antenne and printed their figures upside down. But the figures were accurate enough to show that these were really parasitic copepods belonging to the family under discussion. Miller in 1776 showed that these ‘‘antenne” were egg strings, and he also found and described the true antennx. But he blundered in regard to the eyes as badly as his predecessors had done in regard to the anten- ne, mistaking for them the sucking disks on the frontal plates and fail- ing entirely to find the true eyes. Hence he introduced his specimens under the genus name inoculus, a name which survived for many years. Slabber (1778) described and pictured one of the Caligine under the name Oniscus lutosus; he also delineated the antennz and many of the other appendages correctly and his figure is right side up. Miller in a second paper (1785) corrected his previous error by dis- covering that the sucking disks were not eyes. He then realized that these copepods could no longer be classed in the heterogeneous group known as Lrnoculus, and accordingly founded for them the genus Caliqus. But again he blundered, for the very name“ tells us that he did not find the true eyes, but considered these parasites to be blind. Stroem (1762) was the first to study the habits of the genera from living specimens, and he has given us many interesting observations. A few additional data have been given by Leach (1813-14), Lamarck (1818), Johnston (1824), Desmarest (1825), Burmeister (1833), Rathke (1843), Baird (1850), Kréyer (1863), Heller (1865), Claus (1875), Hesse (1877, 1883), and T. Scott (1894, 1900). But although this list of names looks quite formidable they have really given us almost nothing upon the habits and development of the group. Johnston established for the first time the external differ- ences in the sexes of Cal/qgus by describing in detail a male and a female of Caligus curtus from the cod. @ Caligus, from caligo, a medical term for blindness or weakness of the eyes. 482 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. XXVIII. But the life history was so little known up to 1852 that one of the developmental stages, the chalimus stage, was regarded as an entirely distinct genus, and several species were described by various authors. F. Miller (1852) and Hesse (1877), however, explained the chaltmus correctly, and recently A. Scott (1901) has given a brief life history of Lepeophthetrus pectoralis, in which the chalimus was still further explained. But Scott states plainly that he has not worked out the changes which take place in the developing embryo, so that we are still left with only a general knowledge of the metamorphoses and without a single authentic life history. The work of American authors upon these genera is somewhat superior both in quality and quantity to that upon the Argulide. Thomas Say, in his account of the Crustacea of the United States, published in the Journal of the Academy of Natural Sciences at Phila- delphia in 1818, mentions two parasitic copepods, Pandarus sinuatus, found on the dogfish, and another which he calls Binoculus caudatus on Callianassa, the latter being evidently a species of Caligus. Fol- lowing him came an admirable monograph by Dana and Pickering (1838) upon Caligus americanus (= C. curtus), which was the best account of a single species published up to that date and which remained without a rival until Scott’s memoir just mentioned (1901). The subsequent American papers came at considerable intervals. Dana published several, which were entirely systematic, from 18438 to 1856. Smith in 1874 recorded all the species found in Vineyard Sound and adjacent waters, while Rathbun gave (1884) an annotated list of the species found in American waters, and in 1887 described a new species of 7rebius from Vineyard Sound. And yet out of more than 100 species belonging to the genera here considered only 7 have been reported from North America and 6 from the West Indies. It is time, therefore, that the lists were thoroughly revised, for these parasites are as common upon the fishes of our own coast as they are in European waters. The following account is drawn from all the sources here mentioned and many other published papers; from the records of the United States Bureau of Fisheries; from manuscript notes by R. R. Gurley on The Vermine and Crustacean Parasites of Fresh-Water Fishes; from very valuable manuscript notes and drawings by Richard Rathbun, J. H. Emerton, J. H. Blake, and $. I. Smith, all of which were kindly turned over to the author by Mr. Rathbun; and last of all from the author’s own personal investigations extending over several years. ECOLOGY. Advancing from a study of the Argulidee to that of Caligus and its associates the first thing to be noted, since it is the key to most of the changes we meet, is the fact that the female of these species carries j for the oop 4 hese re tas faed Lipa). Ee Hiniodl ine which they obtiin while apork Loe host's ba dy they are penta: tle sayren of their food. : incesitives are fox chmainiug, rather than bes miving i. ! about, aud: adult fuales, almost mlyways aang ek ina | ‘pew son wate hav 9 aoa des. Myon Hier he ae “ag s hawyseaey cinkrye; ~é. - lai aati Mes i om TE jal rele ad the meteor a aba: » iP son ct sae? rdne id . piel aise Mes nh iets Hegestod sine Me | re SA al Femeni igi! ee PER AGE Ninnirs a So oa ii ic fe Bi iolan shew ae : ee nes ae ao AE : sil ciate hla, bp st | a5, % aks Tye i sus aj to (aie. ms ae igs) ers SS Gee is Miss ae a Pe Rene y vo Sa chat Mie sooo iver: ; ey noniage nS Re oy felenini meee a ileaak Laer salad iy drt. Lao iy . tt Ne se * eo) No. 1404. PARASITIC COPEPODS—CALIGID H— WILSON. 483 her eggs about with her like most of the copepods. This habit neces- sitates several departures from the conditions found existing among the Argulide. In the first place we must look for a greater difference between the sexes both in their morphology and in their habits. The genital seoment of the female is considerably larger than that of the male, and usually the first antenne are larger and stouter. On the other hand, the second maxillipeds are larger in the male, and the abdomen is often composed of two segments, while the female has only one. The increase in the genital segment of the female, together with the heavy egg cases which she has to carry, restrict her freedom of motion. And hence while both sexes can swim about freely it is only the males which can be expected to compare favorably with the Argulide in this regard. This sex difference is particularly emphasized during the breeding season or just at the time when there is the greatest incen- tive for free swimming. That this restriction of the female’s motion is at least favorable to degeneration can not be doubted. But at the same time we have to remember that all the copepods save the Argu- lide are burdened in the same way, and yet all free-swimming forms are able to combat the condition successfully. The condition in itself, therefore, is scarcely enough to be regarded as the first step toward degeneration; we must seek something more. In ordinary free-swimming forms the female, even when burdened with her egg strings, must move about in search of food. In fact, she needs food more then than at any other time. Again, in the Argulidee, the female deposits her eggs upon some con- venient surface away from the body of her host, and such deposition becomes. not an incentive merely, but an imperative demand for free swimming. The males follow the females at these times and also search for them from fish to fish. Caligus females, on the contrary (and the same applies to all para- sitic genera), carrying their eggs about until they hatch, find the sur- face of the fish’s body one of the best possible positions to secure good aeration for the eges and to discharge the nauplii when they are sufhi- ciently matured. Finally these parasites feed upon the blood of their host, or at least upon something which they obtain while upon the host’s body; hence by remaining here they are nearest the source of their food supply. In short, all the incentives are for remaining, rather than leaving the host and swimming about, and adult females almost always remain upon the fish, even during the periods when they are without eg strings. The only inducement in these forms to free swimming on the part of the female would be that which is common to all parasites, plant 484 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. XXVIII. and animal alike, namely, the original search for a suitable host. But this operates in developmental rather than in adult stages, and it is a significant fact in this connection that nearly every female of these P=) genera which has been captured in the tow has been immature. The mechanical hindrance afforded by the egg-strings, together with the strong incentives just enumerated for remaining upon the body of the host, may be fairly considered as constituting the first step toward degeneration. Let us now look at the mode of locomotion in these venera in order to discover the second step. LOCOMOTION. There are two modes of locomotion as in the Argulide, a free- swimming and a scuttling motion. The presence or absence of the latter has a greater significance than has hitherto been accorded to it. By watching specimens of Argudus and Caligus in an aquarium it can be seen that the latter are really the better swimmers. This is due to the increased surface of the first three pairs of legs, particularly to the large lamina or apron which connects the third pair across the ven- tral surface of the body. These legs furnish a swimming organ which propels the copepod through the water with strong and swift move- ments. Often the motion is so erratic and persistent that the animals seem to have fairly gone mad, dashing frantically about, turning sum- mersaults, rushing for a distance along the sides of the aquarium, or scuttling back downward across the under side of the surface film of the water. Equipped with such a swimming apparatus it would nat- urally be supposed that they would put it to frequent use, but we have already seen that they lack the incentive. Asa matter of fact, mature females of but one or two species have ever been taken with the males at the surface. 3 Furthermore, as will appear in the descriptions which follow, these few specimens were all of the genus Caliqus, the species rapaa being most commonly secured. The other genera here treated do not show as much inclination to free swimming as Cadigus and there are but one or two very doubtful records of their capture in the tow. Indeed, A. Scott goes so far as to conclude from a series of careful investiga- tions that *‘ Lepeophtheirus throughout the remainder of its life and under normal conditions remains on the same fish that it attached itself to at the beginning of the chalimus stage.” And the same might probably be said with regard to Anuretes and Trebius. When we consider the amount of surface towing conducted every year under the auspices of the United States Bureau of Fisheries, the scarcity of these parasitic forms can only mean that at least the mature females are not accustomed to swim freely at the surface, but only do so under extreme provocation. ff ’. On Blatt PUT § Le} | “ti ye rs ret ticalby. tie “¥ ‘ s never. weed thee: : ‘ MTORR SPL aR UE 3 Ouse Hut have, Winitging bout a0 Beh: ‘v4 re shiehtost yroyocAtion Kener, bern cent itil Riles, eek! the ability 16 mows nthe body af their ts itty any trendlom | : rae bs 4S th stil} #! ak at 4 Cit 7‘ ? tit : fin vement a, and : ‘they: Felain Filly the avilitin | 2wim they aimout ert never ext, Tol only” pernain LEPINE Cones hess ail their lives, ty acnselres. int si: rhe wpot. aid ptay the ce: coking : rag stages ot fone ele nee ined No. 1404. PARASITIC COPEPODS—CALI GID E— WILSON. 485 Such a change in habits, constituting as it does a long step toward that fixedness of position which precedes radical degeneration, must have some adequate cause. These three genera have practically the same swimming apparatus as Caligus, and if it is never used there must be some preventive influence which operates in their case but not in that of Caligus. In the author’s opinion this influence may be found in the presence of sucking disks on the frontal plates of Caligus and their entire absence in the other genera. Their presence gives to Caligus the same scuttling motion as Argudus obtains from its first maxillipeds. In this way they move about over the surface of their hosts with great rapidity and upon the slightest provocation. But the other genera, lacking the sucking disks, are dependent upon the second antenne and the maxillipeds for locomotion over the surface, and can not conse- quently move about with any rapidity. For this reason they do not change their position as often as Caligus but remain a long time fixed in one place. Indeed, when an attempt is made to remove them from their host, only the males and immature females move about in order to escape. The mature females usually settle down 7m s¢tw and only cling the more tightly. When removed from their hosts and pliced in aquaria these genera settle upon the bottom or sides and remain sta- tionary for long periods, in marked contrast to the restless activity of Caligus. This fixity of position can not help reacting unfavorably upon any tendency toward free swimming which might still be retained by the copepod. To recapitulate, then, we find that none of the Argulide exhibit degeneration or even any tendency toward it. They have all retained completely both the ability and the inclination to swim freely and to move about over the body of their host. Among the Caligine the genus Caligus possesses even more ability than Argu/us, and the males and immature females retain practically the same incentives. But for the mature females every influence oper- ates toward remaining upon their host, and they are very seldom cap- tured swimming freely. All the species of Caligus, however, still move about over their host’s body upon the slightest provocation. Other genera, being destitute of lunules, lack the ability to move about on the body of their host with any freedom. This acts as a still stronger damper upon their movements, and although they retain fully the ability to swim they almost never exer- cise it. They not only remain upon one host all their lives, but they also fasten themselves ina single spot and stay there continuously. They thus exhibit the initial stages of degeneration, whose next step is to be a partial loss of the ability left unused. While speaking of locomotion mention must be made of a pernicious habit common to many of the Caligine. This consists in crawling up 486 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. XXVIII. the sides of the dish or aquarium as far as possible above the surface of the water and remaining there till thoroughly dried, and, of course, dead and worthless. For this reason it is very difficult to keep such species alive for any length of time. Even to carry them from the collecting ground to the laboratory, or to keep them alive while being examined, it is necessary to carefully stopper the bottle or to cover the dish, so that the air above the water shall be so saturated with moisture that the copepods can not dry in it. Fortunately this disagreeable habit is practically confined to the genus Caliqus. and the other genera make quite tractable subjects for aquaria. This is particularly the case with Lepeophtheirus, and A. Scott states that Z. pectoralis may be kept-alive ‘‘in sea water for upward of six weeks after removal from the fish.” PREHENSION. The organs of prehension include both sucking disks and claws; the former are confined to a few genera; the latter are common to all tne genera. The arched carapace, also, in all the genera, acts as a large sucking disk, its margin being pressed close to the surface, and the contact sealed with water and slime. This constitutes a secondary organ of prehension, vastly more effective than in the Argulide, since its margin is made continuous posteriorly by the broad lamina connecting the third swimming Jegs.- When flattened against a sur- face by muscular contraction and then released it works very powerfully. The claws constitute the terminal joints of the second antenne and the second maxillipeds, the entire joint functioning and being capable of strong flexure upon the basal joint. It seems probable that these different organs of prehension are used in different localities upon the fish’s body. The lunules and the suc- tion of the carapace afford the principal means of prehension on those portions of the outside surface of the host which are covered with scales. There is an integument over the scales, to be sure, and in many of the fish which serve as hosts the scales have small spines upon their free surfaces. But the integument is so thin and the spines are so small and weak that they afford but a feeble hold for claws. There is no chance to bury the claws sufficiently to withstand the ordinary friction of water, to say nothing of that of sand or mud, which must be overcome on the ventral surface of such fish as the flounder, skate, ete. The fins, on the other hand, have no scales and the covering integument is firmer and thicker, and affords an admirable material in which the claws may fully bury themselves. So that although the tail and other fins must, from their movements, subject the parasites to considerable additional friction, this is more than counterbalanced by the superior hold which they afford. The blood vessels also are more oer a ; rey Ove with jeterec i Btomnore: bat tae chy Tees Bre wad. afics CP BLUE) ; ST epeeeaike . Csi: SPAT Ooms 7 merited ah wrehensian ty 4) HGP T ER Ae Ove. CHa mane parasite fron. 4 tery ares oft seis Fit i dew ret) ae Le Bey (eNO t I t Oe ey yyy orfy ee a4 0 ‘a rari VI i hf ; iM} , Lee S. $ hho it y 9 ; tT i ok i : r" ’ * ‘ 8, ‘ Ve) y Ly) rhe AN y 1 { : Tf at WV! i { eee | \ res : ; ‘ a \ LW) t ? Ps Wel ' PR RT ee ; i ! e} ; < {i \ ' ER ER rt a ; : ! if - a. 4 % hE tat I L bat LIT es ly ‘re Vee eae } . : : _peOmetA iF boat W : ba ig Ua | TG Albee as as SMPaCe OF SUC fishies Lie Paige Hi. baie, wR irate my eT ae yw 1 ey oa. b , ; 1 A frequeot mae ON .- ORTH. Pity) Cae aes | a at ceva! } OY freee, | ew « . - iA . } . . \ ji Beationed form and the préheustie powers of the warasits neral bing: 2 Plas PUM ELSI tice antl Cyivek wz ETE thre aos freq nent Fof the ne igri ads, bith! iy win wihely hy resent TUT eR nel 0 bere: | tod in the host: bist. "Chey toy eee: " shige ‘pe Surface’ or ity the veil} ip only found diside tha eit. : the most motu hls ins ona poral of if tihiges f ‘Bovita, - On: thie: ‘outs f . oxpe ety Abe: peetah for aicagham nt ant foo No. 1404. ARASITIC COPEPODS—CALIGID A— WILSON. A487 easily accessible in the fins than under the scales. These two reasons are sufficient to explain the preference of copepod parasites for such localities. It might be inferred that in those genera which are destitute of lunules there would be a somewhat stronger development of the claws. Possibly they are a-little larger and stouter, but the difference is very slight, and after careful examination it does not seem sufficient to warrant any statement. This method of prehension by claws renders it more difficult to remove the parasite from its host. Cadigus comes off easily, but it takes a decided pull to loosen one of the other genera, and often the posterior part of the body will be torn away from the anterior without weakening the hold, as noted by Scott. Long experience has taught that the best way to remove these para- sites intact is to slip one end of a pair of broad-tipped forceps well under the carapace and lift the copepod off quickly as one would a limpet. Connected with prehension are the various devices to prevent slip- ping backward upon the fish’s body. We miss in this group the spines upon the ventral surface of the carapace and the roughened plate with its posterior teeth on the basal joint of the second mavxilli- peds, which were so common amongst the Argulide. But we find instead a small plate that often bears spines upon the basal joint of the first swimming legs, and a sternal fork. The broad lamina joining the third legs also, when applied closely to the surface, must act as a powerful preventative to slipping. And these creatures need something that is powerful for they are often found upon the ventral surface of such fish as the flounder, halibut, plaice, and skate which frequent the bottom and often bury themselves entirely in the sand or mud. | The friction at such times must be very great and tax to the utmost both the flattened form and the prehensile powers of the parasites. HOSTS. In general the Pleuronectide and Gadide are the most frequent hosts of the Caligids, but many widely divergent families and genera are represented in the host list. They may be found anywhere upon the external surface or in the gill cavity of their host. while a few species are commonly found inside the mouth, the most notable instance being the new species of Ca//gus from the Bonito. On the outer surface they often prefer the fins, especially the pectorals since these furnish good opportunities for attachment and food as already explained. And then as the parasite usually seeks the underside of the fin it must also be protected in great measure by the latter from the friction of the water or mud through which the fish is passing. 488 PROCEEDINGS OF THE NATIONAL MUSEUM. VoL. XXVIII. Many species show a tendency to congregate in certain places to the almost entire exclusion of the rest of the fish’s body, as in the case of Caliqus bonito and Lepeophtheirus pectoralis. While many of the species stick to one particular host there are others which change hosts from time to time and which are able like the Argulide to live temporarily upon almost any fish that may be available. Caligus rapax easily takes the lead in this, having been found upon twenty-five or thirty different fish. A few of these like the flounder and cod are regular hosts, and an examination of a very few fish is almost certain to reveal the presence of this parasite. At the right seasons also the chalimus stages of development may be found attached to the fins and scales of the same fish. But for the other hosts there is often a record of only a single specimen which was evidently a straggler and took that particular fish until it could find something better. FOOD. These parasites feed upon the blood of their hosts which they obtain in the same manner as did the Argulids by burrowing under the scales or piercing the skin on the fins with their maxillipeds and proboscis. This blood, filling the central digestive system, may often be seen as a dark streak through the body, and is sometimes véry prominent in transparent specimens. When taken from the fish those specimens usually live the longest which have the most blood in them; the latter seems to digest slowly and may often be seen for several days in the intestine. Many authors write that these parasites, or some of them at least, feed upon the mucus of the fish’s body and that no blood has ever been found in their stomachs. :; This statement seems to rest entirely upon the fact that no red color can be seen in their digestive organs. A. Scott says of Lepeophtheirus pectoralis, ‘*‘ when taken directly from the living fish and placed under the microscope it rarely shows even the faintest trace of red coloring -matter in the alimentary canal.” But the same author concludes on the next page that this species feeds to some extent on blood, and a little later he adds ‘‘they do not hesitate to eat their comrades when these become feeble.” For animals which will do this mucus must be a rather tame and inadequate food. It is difficult to determine what the food really is, but there are sey- eral considerations which will help us to form a rational judgment in the matter. In the first place, it makes a difference what part of the fish’s body the parasite is taken from, whether it shows any red in the digestive organs or not. If taken from the gill cavity the red is nearly always prominent, while it seldom appears in those individuals taken from the outside of the body. Some species are always found in the gill cavity and they . ne cain | . baat «° wird hi are yee it 0 riven gi ine LK o- » Cul Lepr) ‘iu Y. WwheR Samy) chad the sane cifforendc SETyY, LEN RV IES iis re ne hi Bestiv: inns a wie ai eee i: co id how BN Ae Rd be content to mm | Pits old bloedsnuckin ge eshte Padaptnd for that purpose. aK Li: vetting” oty the fetts ele ; } ast bgt J s - e Pai Buide Pie any aidrenge in verte preys f fetal, ae » kiteang themalive dn a te i No. 1404. PARASITIC COPEPODS—CALIGID 4— WILSON. 489 always show blood in the alimentary canal. Other species are always found on the outside of the body and they are the so-called mucus eaters. But there are still other species, like Caligus rapax, which may be found in either place, and in them we find the same difference. In explanation we must remember two facts: The gill cavity is the easiest place to get blood on the fish’s body, and it is very possible that such a species as C. vapav may slip into this cavity to get its food and then slip out again to the exterior of the body. Consequently when taken in the gill cavity it would have just finished eating, while on the outer surface of the body the blood may have had time to par- tially digest. The second fact is that all these genera are supplied with powerful digestive glands unlike the Lerneans. We shall see later (p. 513) that one pair of these glands are situated in the anterior part of the cara- pace and pour their fluid upon the food as soon as it strikes the stom- ach. Only freshly aerated blood, in or near the fish’s gills, has a deep red color; that in the capillaries of the skin and fins is not very red when swallowed. Hence it would not take very much of a digestive fluid to remove the color entirely. It is very suggestive to note in this connection that the adult Ler- neans, in which the food is so red as to leave no doubt of its nature, have no digestive glands. During development, however, there is a digestive gland, and the contents of the alimentary canal are not red. It is scarcely possible that the young Lernean eats mucus while the adult eats blood. Again, if these creatures are seeking mucus for food why do they not choose such fish as are most bountifully supplied with it? And how dees it happen that they always hunt out those places upon the fish’s body where the skin is unprotected and the thinnest? There is more mucus on the scales than anywhere else; why should they choose the fins or the inside of the operculum? Finally, the mouth parts of species, which it is claimed eat mucus, are similar in every particular to those of species which are acknowledged blood-suckers. The eating of mucus, then, must be an acquired taste, and it is difficult to understand how an animal with its mouth parts fitted for sucking blood should be content to merely sip mucus while it still retains enough of its old blood-sucking habits to choose the places on the fish’s body best adapted for that purpose. These parasites are very susceptible to any increase in temperature, and a rise of a few degrees will speedily prove fatal. This is the chief source of difficulty in keeping them alive in aquaria. A. Seott gives 16° C. as the limit for Lepeophthetrus pectoralis, and experiment has shown that other species do not differ much from this. A general average of all the species experimented with would raise this limit slightly, to 18° or 20° C. 490 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. XXVIII. On the contrary, they can withstand a very great decrease in tem- perature. Scott states that the aquaria containing Lepeophthe‘rus pectoralis were frozen several times without injury to the parasites. Although this experiment has not been tried upon other species, there is no reason to doubt that they could withstand as severe cold. Repeated trials have shown that the best way to keep these creatures alive for any length of time, particularly during hot weather, is to pack the aquarium or bottle in ice. Those species which are other- wise prone to crawl up out of the water are much less likely to do so, but seem content to remain beneath the surface. Possibly this dis- agreeable habit may be connected ordinarily with a rise in temperature of the water in the aquarium. SUMMARY. 1. The females of the genera here discussed carry their eggs about with them. This necessarily restricts their freedom of motion, but not to a greater extent than in free-swimming forms. 2. Added to the restriction, however, is a lack of incentive to free swimming, since the parasite obtains its food upon its host and finds there the best position for the aeration of its eggs. These two conditions combined constitute the first step toward degeneration. 3. These genera are really better swimmers than the Argulide, owing to the increased surface of their swimming legs, particularly the third pair. But they do not exercise this ability nearly as often as the Argulide, for the reasons just stated. 4. In addition to their free swimming, the Cadigus species also exhibit the same scuttling motion as the Argulidee, and it is accom- plished in a similar manner by means of the sucking disks on the frontal plates. ae 5. In other genera the sucking disks are absent, the scuttling motion is impossible, and we find still less of an inclination for free swimming. Careful observations indicate that these genera remain throughout life upon the same fish to which they attached themselves in the chalimus stage. 6. As another consequence of the loss of the scuttling motion they remain for long periods in the same position upon their host, moving only upon strong provocation. This fixity of position constitutes a second step toward degeneration. 7. For prehension we find the sucking disks in Caligus, and stout claws upon the second antenne and the second maxillipeds in all genera. The edge of the carapace also, supplemented by the broad lamina connecting the third swimming legs, is flattened against the supporting surface and functions as a large sucking disk. 8. To prevent slipping backward under friction there are weak spines upon the bases of the first swimming legs, and a stout sternal No. 1404. PARASITIC COPEPODS—CALIGID A— WILSON. 49] fork between the bases of the second maxillipeds. The lamina of the third swimming legs also renders effective service in this direction. 9. These genera show a decided preference for the Pleuronectidee, and the Gadidz as hosts, but such of them as practice free swimming may be found upon almost any host temporarily. Many of the species, so far as observed, are confined to a single host. 10. These parasites feed upon the blood of their host in a similar manner to the Argulide. They are very susceptible to heat, and an increase of temperature of only a few degrees is quickly fatal. On the contrary, they can withstand very severe cold, even freezing, without apparent injury. MORPHOLOGY. A. Eixternal.—TVhe types upon which Miller founded his genus Ca//- gus in 1785 included several genera beside the true Caligus. Indeed, the only species amongst his types really belonging to the genus was Ca/igus curtus. Hence his genus diagnosis was very broad and would have included practically all our North American Caligine. In the present morphology the statements have been made equally inclusive and are to be understood as embracing all North American Caligine unless otherwise limited. The body of a Ca/zgus is made up of four parts or sections, a cephalo-thorax, a free thorax, a genital segment, and an abdomen. The cephalon bears seven pairs of appendages, namely, antennules, antenne, mandibles, first and second maxille, and first and second maxillipeds. The three anterior thoracic segments are fused with the cephalon so that the cephalo-thorax bears three pairs of swimming lees in addition to the appendages just enumerated. The free thorax consists of a small segment carrying the fourth pair of swimming legs and the genital or reproductive segment. The latter has in both sexes a pair of appendages which in the male are very evidently rudi- mentary swimming legs of the fifth pair. In the female they are often so reduced as to be recognized with difficulty, but their presence is sufti- cient to show that this segment must be regarded as a portion of the thorax if we are to be consistent in our nomenclature of the crustacea. Hence, while retaining the designation ‘* genital segment,” already in general use, it will be understood that this is really the fifth thoracic segment, the second free one. It varies greatly in shape in different species, in different stages of development in the same species, and in the two sexes. In the male and in immature females it is always smaller and often approximates the abdomen closely in size. But as the female approaches maturity it increases greatly and becomes usually much larger than the abdomen. Furthermore, in undeveloped forms of both sexes the rudimentary fifth legs are relatively much larger than in the mature individual, and may commonly be seen as a pair of large lobes or processes clearly 499 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. XXVIII. differentiated from the remainder of the genital segment (5, fig. 1). As development progresses these lobes become assimilated more and more with the body of the segment, until at the last they are oftentimes invisible except from the ventral surface, and then only after careful examination. Owing to this extreme variation in size and shape the greatest care must be exercised in comparing different specimens for purposes of classification. The individuals compared must be alike in sex, in maturity, and even in the period of pregnancy if the size or shape of the genital segment is to have its full significance. Fortunately, one breeding season follows another so rapidly that the female is never left for any long interval without her ego strings. Hence, in collecting these parasites, fully ripe females are very : largely predominant. On being pre- served the egg cases become very brit- c tleand break off easily, but examination \ Wi, will quickly reveal the fact that they v have been present, which of course is allthat is required. In the Key which is given later (see p. 555) the shape of the genital segment is made one of the y, \ final means of determination after the \ other more important ones have been exhausted, and even then it must not be given too much prominence. The length of the egg strings and the size of the eggs vary greatly in different species and in different indi- viduals of the same species, and the best that can be done is to give the Fie. 1.—YOUNG FEMALE OF LEPEOPHTHEIRUS general average. The size of the egos EDWARDSI, SHOWING THE FIFTH PAIR OF f ; SWIMMING LEGS AT THE PosTrRIOR cor- 1S always a better guide than the NERS OF THEGENITAL SEGMENT. a.l., ANAL number LAMIN#; 5, RUDIMENTARY FIFTH LEGS. CSBP SSS To. Like the genital segment, the abdo- men is usually simple, but sometimes two-jointed, this condition occurring more frequently in the male. There are two species of Caligus also in which it is three-jointed, C. coryphene and C. angus- tatus, and another in which it is four-jointed, C. aliuncus. (See Plates VII and IX.) The abdomen is terminated by two processes, one on either side of the anus, and each furnished with three or four plumose set (a. 1, fig. 1). These processes have been given different names by different authors. Milne Edwards calls them ‘‘ lames caudales;” Kréyer desig- nates them as ‘‘halevedhaengene” in Danish, while in his Latin diagnoses they are simply ‘‘appendices;” Heller speaks of them as Aa ranges noth. i ih fey shh ped has fe Giirintes bas mak * Maivabel Geir rcady” white Bassett . a them tbs SOc tattost rhe ten,” faa i ‘| ' cig: on 4 z ? a any j a ty 4 , peers wer aly torts : A PLE s Pn te} WS PCO Tae eo in Meow tision' bah ths 02 th then. anal ala ba 3 ingg a Bpane, anal. papi! ye ore weihus ew con! ¢ mesoomnents, ich beating a steile pain of | rf bLUnited with th 1. anne bdoiicn: of frombne bo dow ee Pdunat Oh or ten itn Lee DEVE re bee pe. weet hy ee ‘neti S. Rive t BEURIIACE Pak } i eats is usually increased by an incision at the enter bwo Plates meet, er oy an. omen lidn extdading tor mope meither side: fn rare Hobs hee Ne tbe niger +) takes plicd, ee: A mde pointot hye protrusion. of thi . . it the form ofa batik or rostrum {Catigus d Ad a drewreeycanis) Hither form presents a, si arta 3s ab ater HO aati, in. Avipnisian | é is Hits No. 1404. PARASITIC COPEPODS—CALIGIDA— WILSON. 493 ““Schwanzanhange,” in his Latin diagnoses as ‘‘ appendices caudales;” Claus calls them ‘‘Furcalanhange,” in Latin ‘‘foliola caudalia;” Gerstaecker designates them as ‘* Endgabel (Furca);” while Bassett- Smith speaks of them as ‘* caudal plates.” There are several objections to these names. In the first place, most of them preserve in some form the old name of *‘‘tail,” given to the abdomen, which was entirely a misnomer. The use of ‘‘furca” or *‘fork” is even worse, for we already havea furca upon the ventral surface of the carapace, and the repetition of the name for a very different appendage could not but breed confu- sion. Why not apply to them the term ‘‘anal,” since they are always situated beside the anus, and thus get a term to which there could be no objection as a misnomer and which would be free from any danger of confusion? Let us call them, then, anal plates or laminz, as we called the appendages in the Argulidee, similar in position but differ- ent in shape, anal papillee. There is thus a cephalon bearing seven pairs of appendages, a thorax of five segments, each bearing a single pair of appendages, the first three. united with the cepbalon, and an abdomen of from one to four seoments, the last of which bears the paired anal lamin. The cephalo-thorax is strongly flattened dorso-ventrally and is coy- ered with a hard shell or carapace, which serves to protect the softer parts underneath. In structure this shell is like that which covers the anterior portion of the body in the Argulidee, but its shape is consid- srably different. Bt the first place, the anterior antenne, instead of being concealed beneath the carapace, form a wide Rene eee” border across its ante- rior margin, their free ends standing out prominently on either side. In six gen 5, Pseudoculigus, Caligodes, Synestius, Homototes, and Parapetalus—the frontal plates thus formed carry upon their ante- rior margins sucking disks or lunules. In the other genera they are perfectly plain. These lunules often stand out prominently and, with the plates themselves, give a squared appearance to the anterior margin (Plates V, VI, XI). This is usually increased by an incision at the center where the two plates meet, or by an emargination extending for some distance on either side. In rare instances just the reverse takes place, and the frontal margin is made pointed by a protrusion of the plates between the lunules in the form of a beak or rostrum (Cal/gus heemu- lonis, trritans, and murrayanus). Either form presents a sharp con- trast with the evenly rounded anterior margin in Argulus. Again, instead of a single median posterior sinus, there are two, one on either side, leaving a median lobe between them, which is usually half the*entire width or more. bo Proc. N. M. vol. xx viii—04-——32 AD4 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. XXVIII. But the regions of the cephalo-thorax are practically the same and are very similarly arranged in the two. As boundaries of these regions we find grooves similar to those in ny Mt ; ( TO ih tn RS Lil Fic. 2.—ADULT FEMALE OF CALIGUS MUTABILIS, SHOWING THE BODY REGIONS AND THE AREAS OF THE CARAPACE. A., ABDOMEN; C. A., CEPHALIC AREA; E. §., EGG-STRINGS; F.P., FRONTAL PLATES; F. S., FREE THORACIC SEGMENT; G. S., GENITAL SEGMENT; L. A., LATERAL AREAS; T. A., THORACIC AREA. the Argulide but differently arranged, not merely in the different genera, but in dif- ferent species as well. - In general they may be described as fol- lows: A pair of longitudinal grooves, one on either side of the mid-line, more or less parallel with it and removed some distance from it, correspond with the sides of the horseshoe suture in the Argulide. But they extend backward farther, reaching the posterior margin of the lateral lobes, while they do not reach forward to the frontal margin. They form the sides of a large Jetter H and are connected by the third groove transversely at or just posterior to the center of the carapace (fig. 2). The carapace is hinged along these sutures and capable of some motion -upon them, as in the Argulide. On the outside of the lateral grooves are the lateral areas, extending back in a lobe on either side of the carapace much narrower than in Argulus (i. A.). 3 The transverse suture marks the junce- ture of the head and thorax so that the central region in front of it is the cephalic area(C. A.), while behind it is the thoracic area (T. A.), the former being usually the: larger. These three grooves are present in practically all the genera and species. In addition there are others which occur with more or less frequency. One of theseisa horseshoe-shaped groove extending from the suture between the carapace and the frontal plates backward around the eyes. It is similar in shape to that in the Argu- lide, but as the eyes in the two families are entirely different it does not corre- spond in morphological significance. There are also grooves at the bases of the free portions of the first antennee which extend inward on the carapace for a short distance, while others appear often in the anterior portion of the lateral areas. iO er ‘ scoala 4 rae Vazem ulonie piu a Loa fyi te Gloiopaee”) we TX, XVIT, XIX; CERT. . phites { iy if; RIC Se weeabed from the CALVETACK in alt ia at considered by ag irreculap wreove made up of sey onal + Baa ‘ ‘ I Fe Lt be 7 J { : i} >. i \ : / : i / Ads ys}. Pi i ; Wi u WAAL Oe, Me ril a, ue fj by : AS + i M xt a Fs! : i = 7 j : t aul ~af j ; € . : : nm os ' i i ' ‘ : im : : b ak pple mermerve as 2 rst id | tt: F eae ‘ é - ‘Se Ee, " th it x , Fal bh) ‘ i r : Pig a } " ror: ty Q ine toward yt ewe ° £ } nl ; + ‘ ; ws rad : : . ¢ a ‘ . Pera. Oh LITO Ttanengh hy t i Ne) Ci ‘ vei . @ gland Which secreted the substance of the Hlament, : Kini gy @isks, which in’ ¢ igus Rerve both Jor prebension anc PS are of pecubar Construction. raser bling nes Dine ‘body er i hot the shucking disks in Arenal ‘Re hbnt rather the free: Dordér, They consist of a short and rather fatwone of vs sap fer fh const tae rs aby Se stance: a cdo wh the ventral or fel xO 5 bites that « enOss section would take. the total nl her than a tircle. ‘The membrane ‘is supported by: ¢ F id many) Aas =) See Shans > ry simi im . No. 1404. PARASITIC COPEPODS—CALIGID 4-— WILSON. 495 Rarely a second transverse groove is found in front of the crossbar of the H as in Caligus hemulonis and C. aliuncus and in Glotopotes ornatus (See Plates LX, XVIII, XIX, XXIII). The frontal plates (F. P.) are separated from the carapace in all the genera here considered by an irregular groove made up of several symmetrically arranged curves. These frontal plates are really the basal joints of the first antenne, as can be readily seen in following the development, and they thus correspond in function to the hooked claws on the base of the first antenne of the Argulidee. The two plates do not quite meet at the center, but are separated anteriorly by a deep and very narrow sinus which marks the former position of the filament for attachment in the chalimus stage, and by a slight projection of the carapace from which this filament emerged. On the ventral surface at the base of the suture there is an oval opening surrounded by a narrow fringe of chitin. This represents the median sucker which is considerably devel- il) u . WS oped and forms an important organ xy of adhesion in the early chalimus Zz s. A stages (s. fig. 3). Its usefulness is Si almost entirely superseded in the adult Caligus by the sucking disks \ which develop during the later chal- imus stages, but in the other genera it may serve as a ‘‘ first aid in secur- | £.. Fig. 3.—THE MEDIAN SUCKER OF CALIGUS ing the animal to its host,” as sug- RAPAX. f.f., FRONTAL FILAMENT; m., AN- S r ~ 0 TERIOR MARGIN OF FRONTAL PLATES; &S., gested by A. Scott (1901). TES ous a . minis SUCKER. In favorable specimens a chitinous rod (f. f.) can be seen passing back from this sucker toward the eyes. This rod is the remains of the filament, and at its inner end may be seen the gland which secreted the substance of the filament. The sucking disks, which in Caligus serve both for prehension and locomotion, are of peculiar construction, resembling not the body or basal portion of the sucking disks in Argu/us, but rather the free membranous border. They consist of a short and rather flat cone of membrane, often split for a considerable distance down the ventral or anterior side. This suture is often so wide that a cross section would take the form of a horseshoe rather than a circle. The membrane is supported by a very few transverse and by many longitudinal ribs of chitin, all of which, however, are simple hairs or threads and not the complicated affairs found in the Argulidie. 496 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL, XXVIII. This cone is often partially or even almost completely concealed by the border of the frontal plate in a dorsal view, so that it is only by turning the animal over on its back that one could be sure whether it has lunules or not. This is the condition with the entire genera Cal/- godes, Synestius, and Parapetalus, and rarely in some species of Caliqus like C. diaphanus. The carapace, like all the rest of the body, is covered on both the dorsal and ventral surfaces by a thin cuticle. At the margin where these two cuticles come together they are fused and form a wide, per- fectly transparent border along the frontal and lateral edges. Being smooth and flexible this border can be applied very closely to the sup- porting surface and forms thereby a tight joint which greatly aids in prehension, as already noted (p. 486). The eyes are situated on the median line, about one-third the dis- tance from the front of the carapace. They are two in number, so closely approximated as to be partially flattened, and are embedded in a mass of pigment which lies wholly beneath the carapace. Each consists of a spherical mass of pigment flattened on the inner side, where it is separated from its fellow by a thin layer of chitin, lined with the same pigment. The lens is spherical and projects about half its diameter from the outer or anterior margin. Behind the lens is a retina made up of a single row of relatively large cells, which are lined on the inner side with a layer of pigment. This pigment is usually black or very dark wine-red in color, while the lens is colorless and perfectly transparent. In quite a number of species, scattered through all the different genera, the eyes are invisible (in preserved specimens) to even the most careful scrutiny. But it seems probable that they are merely concealed by overlying pigment and not really lacking. This point can be determined only by a study of sections which are not at pres- ent available. From a study of the early development we find that these eyes are originally placed much farther back in the carapace and are separated by a greater distance from each other, and that they afterward migrate forward and inward toward the mid line, until they are so thoroughly fused as to appear as one eye with two lenses. The free thoracic segment is small in nearly all the species; it rep- resents the fourth thoracic segment of free-swimming copepods and carries the fourth pair of swimming lees attached to its outer mar- gins (F. S. fig. 2). In all the species figured, with one or two doubt- ful exceptions (C. dubius and C. fallax), it is so much narrower than the carapace and genital segment, especially where it joins the former, as to appear like a wasp waist connecting the two. This appearance is heightened in Caligodes by a considerable lengthening of the seg- ment, The rare instances in which it is figured as double instead of ) ihiito vdeo er’ ina tia) shiny © ients, ‘Danu’s 8 enlareud figiureof th wanital eoment. t oF thi siows also the free Sho ryeied Bs . r mend aa i “a @enital seytmoant (2. S. he, 2) nuine would imple athe Set, ey the Ora Cet ti a . ; ; : , ie oa j : i oh , Lee ; Rta meee oem them, in. thé fenuile the jntarnal o ) “ers 1% tj wert iT | Row 4 iy ae, : : ; | | \ ty eo rt 1? tas i t ' Hhigs ‘ / ‘ U3 Gur b> 154, “Th { \ { : : tires tos . kaye on page ahd 6 Ty op f hi fvies Be watts ‘un . Bees BBY Be Cont oniontly studied theough then ney align i ‘), often markedly so. ‘ane ; as. es | ‘ bat : i rts bn ft a. 4 ; , a Supple. Ih it “pecies, however, it tg Lash lickin PTUs wipher : ; fy \ 1 , ; ; é - , s wilh s , s aa). el EED ULETIEAN emiented. thi ME) tian ky ae ‘1 nt ‘5 “din Glew} it Q ?! TTR ryyvLee 2 Gee Ot) f geay’ ANG ; bhe ahdon : i} thi tha iy : eTrex i¢ o} h n iy) at > ie, i aa to SUG se Cie CAF TUL Oraewy Ati ri he AS we . BOR: bre ; y . ni . . : : pa Pe euongiy with the plump, stork? figure of the fem rhe i” peepee cases (1S. fig, 2) are bylindrieal tubes, 0 y into the ‘valine sl ovidaet yer? near ite exit finder i is! idivided | Lr Be OTT Es by cross rth 1e,-One. Ewa Retr ro exes, 80 that offen wher Che naw have ape t fromthe, eis loft behind a sorb ot nomlted skin wineh retains the exact ({ rr) gin’, bat is entire! empty When full the Se ROE CANES, Stent inferno: to checit-the shi) bty of theif '-Oftentines: t they are relatively ve ry large, at in oe ) diay ainsi, te to sti righ taken: 1 doether are ne . 1D) LDS. sepnienty oe . fete | at} No. 1404. PARASITIC COPEPODS—CALIGIDA— WILSON. 497 single (Caligus alalonge, chorinemt, productus, robustus, and trachyp- ter’) are very doubtful and the probability is strongly against them. For instance, while Kréyer’s smaller figure of C. productus shows two segments, Dana’s enlarged figure of the genital segment of the same species shows also the free segment as single. In several species (Caliqgus irritans, monacanth?, and vexator) the sides of this segment are indented as if for another joint, but there is no actual division and the cases just mentioned are probably the same. Indeed, if these or any other species really had two free segments, this would be sufficient ground for a generic rather than a specific distinction. The genital segment (G. S. fig. 2) is not, as its name would imply, the seat of the reproductive organs proper, but merely of the ducts leading from them, in the female the internal oviduct, and in the male the vas deferens and the spermatophores (see figs. 32, 33, 34). But since in the female the convolutions of the oviduct contained within the genital segment are the place where most of the develop- ment of the egg occurs, it follows that this segment is usually plump and swollen. Its shape varies greatly and is indicated for each of the different species in the keys on pages 555 and 615. In many of the species the walls are so transparent that the structure of the internal organs may be conveniently studied through them. The abdomen (A. fig. 2) is always narrower than the genital segment (except in Caligus hirsutus), often markedly so, and is usually shorter and simple. In certain species, however, it is much longer (Caligus macrurus, pelamydis, scombri, and stromate), and it is also sometimes segmented, this occurring oftener in males than in females. And then the abdomen in the male is relatively longer than in the female, so as to give this sex a narrowed, drawn-out appearance, con- trasting strongly with the plump, stocky figure of the female. The external eg@ cases (KE. 5. fig. 2) are cylindrical tubes, the substance of which is secreted by a shell gland situated in the genital segment and opening into the internal oviduct very near its exit from the segment. The cylinder is divided into segments by cross partitions, one between every two eges, so that often when the nauplii have escaped from the egos there is left behind a sort of moulted skin which retains the exact form of the original, but is entirely empty. When full these egg cases are the most potent influence to check the ability of the female to move about freely. Oftentimes they are relatively very large, and in one species, Caligus diaphanus, the two strings taken together are nearly as large as the entire body. There are twelve pairs of appendages, namely, two pairs of antenne, one pair of mandibles, two pairs of maxille, two pairs of maxillipeds, and five pairs of swimming legs, all on the ventral surface except the 498 PROCEEDINGS OF THE NATIONAL MUSEUM. Vor. XXVIM. first antenne (an’, fig. 4). These latter are attached to the frontal margin of the carapace and project sidewise from the body. Each is made up of three joints; the basal joint is the largest and is in the form of a lamina or plate, which bears a lunule on its margin. The median joint is larger than the terminal and bears tactile plumose set on its anterior and outer margins. The terminal joint is usually more or less club-shaped and furnished with short and sharp spines at and nearitstip. These antennz should be very highly sensitive, if their innervation is any cri- terion, for a large nerve enters each from the supra-cesophageal ganglion, and, dividing and sub- dividing, sends a branch to the sucking disk of the basal joint, to each plumose seta of the median joint, and each spine of the distal joint. The second antenne (an’’) are attached to the ventral surface just posterior to the bases of the first. They are each two-jointed, the basal joint being short and stout and plentifully supplied with strong muscles. The apical joint is modified into a stout pre- hensile claw, which fits into a cup or socket hollowed out of the ventral surface of the cara- pace near its front margin. In the genera under discussion these antennee have become en- Fic. 4a.—VENTRAL SURFACE AND APPENDAGES OF AN tirely prehensile In function, ADULT FEMALE LEPEOPHTHEIRUS EDWARDSI. an’/., and, with the second maxillipeds, FIRST ANTENN#; an’’., SECOND ANTENN®#®; f., FURCA; h yess ih yh > i f m., MOUTH; mx’., FIRST MAXILL#; mMx’’., SECOND t ey are the ¢ lef organs of at- MAXILLE; mxp’., FIRST MAXILLIPEDS; mxp’’.,SEC- tachment in places where the OND MAXILLIPEDS; 1, 2, 3, AND 4, SWIMMING LEGS. 0 5 ike skin is accessible (fig. 5). The mandibles are wholly inclosed within the mouth tube; they are very slender, stylet-shaped and usually four-jointed. The apical joints are visible through the mouth opening; they curve in toward each other and are either serrated or crenated along their inner edges, the number of teeth being twelve to sixteen. _ In Lepeophtheirus the outer margins are smooth, but in Caligus they are sometimes cut into very small acute teeth, eighteen to a > ya Efe ON Yo Cle hs > ol fom petit: Pe Poe Bee = lip, ond Are conn vee There? 0@ . Ppaanaibute: pels. | | first maxille (yx’; figs.4 and 5) are situated near the ae Be of, tho CAL PSL CaS, Th ib otsuieet and a bet & OoOsSterrat LO, the of the i nd Wate Die eta eonsata Of a shivoles leytr in LAE 4 = | ea! FEL * ‘i Sspecies, but sae CWO jou OW BHeCIES OF Cifedue necordans 5 rid her ‘the Mescriptic + hn ni, MEL SONOS es are SWOMGRK. Lin pase and tape: COW AI Pie ( Bie CRey are spori ¢ M " } r = te i | j ; é t ba EEE (FG, ue oe, “ ‘ : So) ag Ly co) iia | hs. maxilla Is “pis ry cH ee cad Manta et an he / ten re 7 : Tey : Tye) SXEVE Me | P : \Vemsan Bemeeine and thus forms a claw: |} peSiinita te that on one of ‘the “\ | LeNntnik { salah ‘ rit u pe i \ = | 3: i bin pot t end ‘mantennm and the i Mxillijped ant £O COUKL Mol { iA| yeh the | beets hodyuntilafter * a / ae ; ag. - i | A a Pathers had heen pureed In ~ : OMe 5 skin. ~P Gsethly ti] ey may { ih ' e. am both sexes. to itritat in [eS ° " wi ind aud so-stinulate the ‘blood; aye Le hy Re heenpus Fit, MoV etean vtRFAcE AXD APPESDAGES ov ak ‘ i ; d Hote are atinched iam : Sy BAIR ON HOW ANIM. ior al part of cae ny WeRG te.) a if ‘Beote COMBI TS tes rept atk the rill (mx din rial ln some spavie extipodite or : WwW Aig. Save ie ok’ fil thys sides 0 thu i of the camp just inside the lateral chitin rods of the lower lip, and are connected with the ventral surface of the carapace by stout muscles. There are no traces of mandibular palps. The first maxille (mx’, figs. 4 and 5) are situated near the lateral margin of the carapace, just outside of, and a little posterior to, the bases of the second antenne. Each consists of a single joint in most of the species, but of two joints in a few species of Caligus according to the descriptions given. In both sexes they are swollen at the base and taper toward the tip; inthe female they are short and blunt and apparently of no service. In the male they are much longer and taper to a slender, sharp point at the apex; each maxilla is also curved over toward its fellow on the oppo- site side and thus forms a claw similar to that on one of the second antenne (fig 5). And their function would seem to be similar, although we must remember that they are shorter and weaker than both the sec- ond antennez and the second maxillipeds and so could not reach the host’s body until after these others had been buried in the skin. Possibly they may serve in both sexes to irritate the wound and so stimulate the flow of blood. In some species of Caligus and Lepeophtheirus Fig. 4b.—VENTRAL SURFACE AND APPENDAGES OF AN ADULT MALE LEPEOPHTHEIRUS EDWARDSI. (For lettering see Fig. 4a.) two minute sete are attached to the basal part of each max- illa which A. Scott considers to represent the exopodite or palp (eno. 7). The second maxille (mx’’, fig. 4) are placed at the sides of the mouth just outside of the suctorial tube. Each is made up of a single joint, stout at the base and slender toward the tip. In Caligus and closely allied genera the terminal portion is undivided while in Lepeophthetrus and.its near relatives it is bifurcated. > 500 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. XXVIII. This terminal portion represents the exopod and in many species of both Caligus and Lepeophtheirus there is also a distinct endopod (e’’, tig. 7), with two sete on its apex attached to the base of the exopod (Lepeophtheirus pectoralis, Caligus rapax, ete.). The mouth opening is terminal or termino-ventral and may be either circular in outline ( Caliqus Lonito, Lepeophtheirus edwards), transversely elliptical ( Caligus ra- pwt), or even strongly lunate (Caligus curtus, Lepeophtheirus pectoralis). Whatever its shape it is always surrounded by a fringe of long hairs. Often in the incision at the center of the under lip is a small tuft of hairs considerably longer yet. In living specimens these hairs are seen to be motile and : they must assist in drawing the Fig. 5.—THE SECOND ANTENNE AND THE FIRST hlood up the mouth tube by mak- MAXILLZ OF THE ADULT CALIGUS BONITO. . 6.26 230 UPPER FIGURE, THE MALE; LOWER, THE FeMALE.. INQ the joint at the mouth opening tighter. The framework of the mouth is quite complicated and consists of two sets or series of rods running lengthwise, connected by others iii hs Me a b Fic. 6.—MOvUTH PARTS. a, DORSAL SURFACE OF MOUTH TUBE OF LEPEOPHTHEIRUS HIPPOGLAOSST; b, VENTRAL SURFACE; C, MANDIBLE; d, MANDIBLE OF CALIGUS BONITO; f, FLEXIBLE FLAP AT ANTERIOR END OF UPPER LIP; r, ROD ON LATERAL MARGIN OF FRAMEWORK OF LOWER LIP. which are transverse. There is first a long rod on either side, running the entire length of the framework along the lateral margins and furnishing the requisite support for the whole mass (1, fig. 6, and 1”, Daas th ce eCORD “ANION, Nae nen ee of MARL Gr PPR RTT EE PAA BONEN be vata ahead hed seit LOW tbs t RRNA RE I vex Ris ey ate 2 peo articulated with tie ventvalsarface of th COLETTE Se Pmuscles wii neVabS OF lower Weenie: Oh Poi tA tened MSbOrh wor CC aligis AOTOe h Pele teooxs ATR. Fi » PAGMI RD TO BHO SL RXOP Ty OM PLE ARELEW SaN?, xi enilel ee the first: (Caligud rerti). Aside iy st ; the sited anton’ ie ikl, hg its aie dat the formed are fehignd with a tuft of hairs filly. tik whieh iringe. iu aaa ast the Siesta rane fe itt, either vids dos nek af) oa 7 Hot No. 1404. PARASITIC COPEPODS—CALIGID 4—WILSON. 5OL fig. 10). These rods are inclined toward each other as they proceed away from the ventral surface; their proximal ends are bent sharply and sometimes carried a short distance along the ventral surface of the carapace as in Caligus curtus. They are articulated at the bend thus made and again near the tip, making them three jointed. At the basal joint they are also articulated with the ventral surface of the carapace, und the muscles which elevate or lower the whole mass are fastened here. The short terminal joints curve inward and nearly meet at the mid line (Caligus bonito, Lepeophtheirus edwardst). Sometimes they are reenforced here at the tip by other small rods which run in toward the FIG. 7.—SECOND ANTENN®, FIRST AND SECOND MAXILLE AND MOUTH TUBE OF ADULT CALIGUS RAPAX, HIGHLY MAGNIFIED TO SHOW EXACT POSITION, RELATIONS, AND STRUCTURE. an/’’., SECOND AN- TENNE; @’., EXOPOD OF FIRST MAXILLA; @/7,, ENDOPOD OF SECOND MAXILLEH; M., MOUTH; mx’., FIRST MAXILLA: mMxX’’., SECOND MAXILL&. mid line parallel with the first (Caligus curtus). The lower lip is stretched over this framework from side to side and projects somewhat in front of the small anterior rods. It is divided at the center, and the edges thus formed are fringed with a tuft of hairs fully twice the length of those which fringe the rest of the mouth opening (fig. 6). In A/ebjon there is a slit at either side instead of a single slit at the center, and the fringe is not much lengthened. In the membrane of the lower lip, between the marginal rods just described, lies a complicated jointed framework of short rods which help support the membrane. ‘Their number, arrangement, and shape 502 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. XXVuI. varies greatly in the different species as well as in the genera. In Caligus curtus there is a long rod on either side of the mid line, the two being approximately parallel to the very tips where they bend in suddenly together and are united for a short distance along the mid line (m, fig. 8). Connected with this united portion are three short transverse rods (t). All of these rods are narrow and cylindrical in shape (Pickering and Dana, 1838). In Caligus rapa there is a large V-shaped rod at the base of the lips (v’), and another (v’’) at the tip, the bases of the two Vs being toward each other and their sides being connected by a series of short, almost spherical rods (s, fig. 9). The V-shaped pieces are strongly flattened FIG. 9.—VENTRAL VIEW OF THE MOUTH TUBE OF CALIGUS RAPAX IN A LATE CHALIMUS STAGE. YT, ROD ON LATERAL MARGIN OF LOWER LIP; s, Vv’, v’’, SHORT RODS FORMING THE FRAME- WORK OF THE LOWER LIP. Fic. 8.—VENTRAL SURFACE OF THE MOUTH TUBE OF AN ADULT CALIGUS CURTUS. (AFTER PICKERING AND DANA.) M, LONGITUDINAL CENTRAL RODS IN FRAMEWORK OF LOWER LIP; t, TRANSVERSE RODS. and much wider than thick, and might well be called lamin instead of rods. The membrane forming the upper or dorsal portion of the mouth tube may be called the upper lip. Like the lower lip, it has a chitin rod (r’, fig. 10) along either lateral margin, but in this instance, instead of being connected at the tip by short transverse rods, the chitinous edge is continuous around the anterior margin (fig. 6). The proximinal ends of the rods are enlarged and flexed, but not as sharply as those of the lower lip, and to them are attached muscles for moving the lip. There is no central framework in this dorsal mem- brane, but the latter is stretched from one marginal rod to the other. In Caliqus curtus and Lepeophtheirus edwardsi the anterior portion of the chitinous margin is bent back in the form of a semicircle, into which fits a more or less circular flap (f) of soft membrane whose front ater immovable’ "Pie ete my arid Dak ay 18 ocaclale Baie : fe bhe whole mouth tule moves together and freely, and eer: af the neath portion Of ibis a8 wmovihiews the yontrnal 7] n Culdouns nth in, itistead of, heirige Bis couvex [ik ie Towey, Ty Ooetae in front oF ae aYTroy Sie mein brecn ith its front odes incised af the Gene and fringed t ‘The etal Siri nt ot Momposed of th: BC maxiiie which th he Sotibined wit) ial ipa. Bat iw geen that beth Dain Sites are Bally fun rely a). And A. } sash has shee yy te iunervation ht vi brs ie big that aap a W'S Ww as. eppeniage A of their es 4 EA Miaps (Pickering ani Dona, 1995). i, Da Daleeed iprc thoi is 9 Ware V-shaped a ite ©, nl another ei at the Wee tose hreiadof thet Pa te Viewrn di ouamack or tus mote ceeene. ‘ UA ACE Osiinin cURrtie, | TAR EB A: Pryce \ : Aa TYNAN ob: LOMA TODIN AL BRA ROUBR o i AN PIANO WONG CR. cada Rt Ey CRAMER RRL: ote Nf Mek oF oe sie aia The: mentfasaiie No. 1404. PARASITIC COPEPODS—CALIGID 4— WILSON. 508 edge is crenated and fringed with long cilia (fig. 6, a). This flap is flexible and capable of more motion than the remainder of the lip, but to call the latter “immovable” (Pickering and Dana) is certainly mis- leading. The whole mouth tube moves together and freely, and cer- tainly the dorsal portion of it is as movable as the ventral. In Caligus rapax the anterior portion of the chitinous margin, instead of being coneaye, is convex like the lower lip, and projecting in front of it is a narrow flexible membrane flap, with its front edge incised at the cen- ter and fringed throughout with cilia (fig. 10). The statement of Pickering and Dana that the mouth ‘‘appears to be composed of the upper and lower lips, united with the different parts of a pair of maxille ” (1888, p- 73) can not stand. Those au- thors made no attempt at any explanation of the position or connection of the maxille re- ferred to, except to state that they corresponded to the first pair of maxillee in decapod crusta- cea. And even this was not stated directly, but ina roundabout fash- ion, for they found a single pair of appendages which they said corresponded to the second max- ille in decapod crustacea, but which they called the first maxil- lipeds. They proved to be in reality the second antenne; it must have been, therefore, the first maxille which they thought were combined with the upper : y Fre. 10.—DORSAL SURFACE OF THE MOUTH TUBE and lower lips. But we have al- OF CALIGUS RAPAX IN AN ADVANCED CHALIMUS p 5 : TAG of f TER ARG . FR ie read y seen that both pairs of STAGE. YI’, ROD ON LATERAL MARGIN OF FRAME 5 WORK OF UPPER LIP. maxille are fully accounted for outside the buccal tube. And A. Scott has shown by the innervation in Lepeophtheirus pectoralis that the claws which Pickering and Dana considered as appendages of their ‘* first maxillipeds” are really the first maxillee. Of the two pairs of maxillipeds, the first are situated about halfway between the apex of the mouth and the lateral margin of the carapace. Each one of this pair is two-jointed, the basal joint moderately stout while the longer terminal joint is very slender and terminates in two or three short and stout spines. Their function is probably that of keeping the mouth clean of foreign matter by a sort of combing motion (fig. 11). The second maxillipeds arise near the mid line, a little posterior to 504 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL, XXVIII. swollen and liberally supplied with stout muscles, while the apical one is a powerful claw curved over inward and carrying a spinc on its inner margin (fig. 12). These are the chief organs of prehension, 2 as already noted, and are usually much larger a in the male. Their relative size, however, varies greatly in the different species and genera; in one they are evidently the chief reliance for clinging to the host or to the female; in another the second antenne are so much enlarged and the first maxille in the male are so stout that these maxillipeds evi- dently share the honors at the least. Lepeophtheirus innominatus is a good exam- ple of the former, the basal joints of the second maxillipeds being so large as to fill the cen- Fig. 11 —FIRsT MAXILLIPED OF tral portion of the carapace (Plate XXVIII). LEPEOPHTHEIRUS EDWARDSI. = ° 0 6 And Caligus schistonyx is-a good example of the latter, the terminal claw of the second maxillipeds being small and very weak while the second antenne are large and stout (Plate V1). In many other species the two are just about equal in strength and efficiency. Between the swollen basal joints of the second maxilli- peds arises the furca or sternal fork, which consists of a stout chitin plate whose tip is bifid, much like an old-fashioned bootjack. It varies consideraply in form and relative size in the differ- ent species, and for some au- thors it serves on this account as a secondary basis of classifi- : Fig. 12.—THE SECOND MAXILLIPEDS OF THE ADULT cation. Itisfrequently of con- Caucus Bonrro. Uprnr rigure, THE MALP, WITH 2 g o : C A LARGE BONY PLATE ON THE BASAL JOINT; LOWER siderable yservice: imi thnisyoinec: sama .ee ie cere tion, and in one or two cases is sufficiently different to serve as the distinguishing characteristic of the species. Witness the double bifurcation in Lepeophtheirus hip- poglossi and L. bifurcatus, and the peculiar form in the genus. G/ozo- potes and in Caligus platytars/, and the entire absence of this append- age in the genus A/ebion (see Plates XX, XXIII). Several uses have been suggested for the appendage. I. C. Thompson thinks that it hy “of 5 From ita. fost to: Renda fhe aug of At a m1 eet Lité there are sevi ral conside rations: ies Maprobal Die, In the ort place” ary ite ages its “teu ey hi Te AOR Sto py to keep the War kae a be vould won kes Lie: parasite’ : ie) jlur arrangers nt te sdnys jie »* ) pant HOVE RL 4 . b : o ; ; ar as cin be cleferniied. ad fd siyviatiye iy ee adits eae vs Bey Saiee Bh a na, ty. t i YUMA ' .) ; i : (} Skat He SLSe ¥ hen Loe LEY Giawen ‘Ss CHD ry ny on rm : : | m3 € 9 ! Ulin ( \ yy 1h eae Sf P ; ee so) ee i ‘ i i O t ta ih the } ; e B SOOOET — 2 it : neha i? ; ! > VF } , t tor ‘4 : ross wit atthe H P ‘ ba bes Sreits, ; 2 j v4 } Ff ‘ My , kivard Wor On OSE YEG! Ga as de loosened whe chiws and HoVing about over tis te Ha , pay ae Jt, womwd this Orvesn iin ; Hoy wweth aaa TREO EASY with: : hy is pillated aren and th PES UPON. Ee) AAS. Tet is mTatayh Peitipeds in the Argulid its. position hatweenthe basex ofthe momaxwiupeds, 15 backward inclinetion.and the entire ah nes Or Pr. billated Areas Wd he Wis Lice i tpern | Ba prolahi| ty to this viet othe Swimming lowe the first aad fourth on he. Uniramose 4 Yall the wenerAa Wille th maine pairs are bisa! oP k Tr Alehion, has the legs all hivamose, but tie fourth pair arb die , 4 - “AR will be sean Eon tie Kew ft ents are kovyerabothér idoabins = in Natt) American. witers whivh bare: aff four pinite wae Be Alchicn, While Cudvxiis and Duethorua have the first ~~ bi the. other ther p42 be nage bipaits HOse, ; a ey 2 oa “ge ad # Seaman evel cgi mas ahic: | aha fibetatly, suid stb Sin pene Va Ber es is i ef : pelinpea: hehe to the: host femahivow aoc Lhe yond, ped: snlagygiik ‘wie? Ghee? vet Opal bie 9a: about That Bese. 2 Meaty, aeere lan hauows at the. ae ae Bi ha Pheinpes inominater : mise we trl port of te ep And’ Culigus tohistonyin. “the: latter, the takiiinal claw of the second masillipeds and very: syeak while the becond antontie Spee ae sar Tk many other species Hie ae two are just about in ees ae vabrength and efficiency: | Betireon. the « ecian Haseat joints af the’ ets THM iepeds atites the fates or sternal fork, which consists of a stout. chitin plate whose’ tip is: bid, Saweh likes ER, old- fashioned | hootinsk. it varies consideraisly in (own and yelative sizo in the sitter : Yenk Species, and for some aa-. “thors ik serves on this, eile. 3 We a Secondury haais of chivsifi- el $i) li mal Uhl wrebe ae venison. ft18 Deni OF Yon, Doss pie Sg are Ee aacieble eevice in this dinee- eae je and | ah basins of — aes. a pe No. L404. PARASITIC COPEPODS—CALIGIDA— WILSON. 505 may act as a support or crutch on which to raise the body of the parasite high enough from its host to render the use of the swimming feet and mouth organs possible. But there are several considerations which render such a function quite improbable. In the first place the parasite uses its feet when on its host simply to keep the water beneath the carapace agitated for purposes of respiration; and there is space enough for this, ordinarily, without raising the carapace at all. Again, the raising of the carapace and balancing it upon this fork would weaken the parasite’s hold enough to render any sudden or unlooked for friction dangerous. And then, if the fork were to function as a support there would certainly be need of some mus- cular arrangement to adjust, hold, and remove it, as occasion demanded; but there are no such muscles in connection with this fork, and, so far as can be determined, no means of adjustment whatever. And, finally, there would be very little demand for such a support, because when the terminal claws of the second maxillipeds are driven into the skin of the host the parasite’s body is ordinarily raised to a greater distance than the length of the sternal fork, and by straighten- ing the basal joints of the same appendages it can be raised still farther without in the least loosening its hold. A. Scott, in the memoir already referred to, writes that the function of the furca is unknown. But it seems at least possible that it may be used for the purpose already suggested, to prevent any slipping backward upon the host when the parasite has loosened its claws and is moving about over the host’s body. It would thus correspond in function as well as position with the papillated area and the spines upon the basal joints of the second maxillipeds in the Argulide. Its position between the bases of the second maxillipeds, its backward inclination, and the entire absence of spines or papillated areas upon the maxillipeds themselves give at least a probability to this view. Of the swimming legs the first and fourth pairs are uniramose in nearly all the genera while the remaining pairs are biramose. The genus A/ebion has the legs all biramose, but the fourth pair are rudi- mentary. As will be seen from the key there are several other genera not represented in North American waters which have all four pairs biramose like A/ebion, while Calistes and Luetkenia have the first pair only uniramose, the other three being biramose. In the first pair the basipod is simple and considerably larger than the terminal joints, except in Ca//godes, where it is the same size. It frequently carries upon its posterior ventral surface one or two spines whose bases are enlarged and which are inclined backward (fig. 13). The exopod is well developed, two-jointed and in line with the basipod. The terminal joint is often appropriately called the ** hand” on account of its shape. 5O6 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. XXVIII. It carries on its outer margin three claws of about the same length, at the outer posterior corner a long plumose seta or a spine longer than the claws, and on its posterior border three stout plumose sete. Occasionally one of the terminal claws is developed at the expense of the others, as in Lepeophtheirus monacanthus and L. quadratus and Caligodes megacephalus. In the genus Glotopotes two of the claws are curiously modified into a three-pronged fork. One or two species have been reported in which there were no plumose setz upon the posterior border (Caligus hemulonis and C. productus). The endopod of these first legs is rudimentary and is represented in some species by a minute joint bearing sete (Lepeophihetrus pectoralis) and in others simply by the setae (Caligus rapax and C. bonito). In the second pair of legs both exopod and endopod are well devel- oped, two- or three-jointed, and plentifully supplied with plumose sete. G\ =) Fic. 13.—FIRST SWIMMING LEG OF ADULT FEMALE CALIGUS BONITO, VENTRAL VIEW. These latter point inward on either leg and are often long enough to overlap on the mid line, thus forming a very effective swimming lam- ina. These legs are almost exactly alike in all the genera. The large basipod carries on its posterior margin a stout plumose seta, inclined backward and inward at an angle of about 45°. The basal joint of the exopod is longer than either of the other two joints and carries a plu- mose seta on its Inner margin and a stout spine at the outer distal cor- ner (fig. 14). The second joint is short, with a plumose seta on the inner margin anda spine at the outer distal corner. The terminal joint is almost circular in outline and carries a row of six plumose sete around its edge and a spine at the outer corner. This exopod is in nearly the same line as the basipod, but the endo- pod is bent inward until in Caligus and Lepeophtheirus it is at right angles to the basipod, while in Glocopotes and Alebion it is nearly par- allel with it, but running in the opposite direction. The basal joint of this endopod is short and carries a single plumose seta on its inner margin. The second joint is the longest of the three and usually the widest, and carries two plumose sete at its distal end. The circular ? eek For this paral: ant it eatries | ete ate eet eX Faeeein ihe éndopor is never Host nes, like: thie waza ita wHociés en ae bird pair of fom ti tens viewte videned out inte a aes i 1OKe ftom either leg hiert wt fowiog ab the wid'tine Gaen solid apran he ange Ack? area, and! offen Bounling the . Thig tans bal « AW LIT Nrobly 1 Be alan; peal, : ' : Si hyi Re Be hss actin Yael ; i g Brepito assist in the preventio Liaw Lie Gaps i @F margin of th some species, | d, The endopot oe t fiwes idheteet, the basal jeunk patie and alniost ficieete ic oh 08 the neste white the joint ia) citcalar. Thee, dxounnhiis two. or chin jeiuted, they Mamed with a. stout iluae. die) de: venta aavince, the tw i Heing the halvusf jsut, lied. dh some speckles: . vints elongmbeud: aap) mtbr sit ese to the mar Bath. robes save ples titully supplied: awit thins heise paste were), heersy : Phe baer, BS ophthaspag ae 4 ; No, 1404. PARASITIC COPEPODS—CALIGID 4—WILSON. 507 terminal joint is set into the outer distal corner of the second joint, which is much narrowed at the end for this purpose, and it carries a row of six plumose sete around its margin. The endopod is never armed with spines, like the exopod, in any species. In the third pair of legs the basipods are widened out into a broad lamina, those from either leg meeting and fusing at the mid line into a single solid apron the entire width of the thoracic area, and often nearly equaling the width of the carapace (fig. 15). This forms a powerful swimming organ and at the same time assists greatly in pre- hension by closing the posterior edge of the carapace and enabling it to act as a large sucking disk. In addition to these two functions, the lamina is also inclined backward, and being stiff it must make a power- ful prop to assist in the prevention of slipping backward. The exopods . and endopods of this pair of legs are very small and are attached to SEE ES CAL