CEIJSTACEA OF NEW ZEALAND. 203 



so-called " epimera " are really the coxre of the legs, Stebbing [108, p. 289] appears 

 rather to favour the first vievr. Against this I may call attention to the fact that, in 

 Phrcatoicits, in the segments of the pleon the pleural portion of the body-ring lias grown 

 out to form a protection to the pleopoda, the coxal portion of which is present, but is in 

 no way attached to this outgrowth of the body-ring, and the outgrowth is quite 

 continuous with the body-ring, not being marked off by any suture or line of division. 

 The same tiling is of course true of the pleon of most Amphipoda. Thus tbese true 

 outgrowths of the body-ring npjjcar clearly marked off from the " epimera," which are 

 either quite separate from the body-ring, or have a suture clearly showing the line of 

 division, a fact that can be easily accounted for if the " epimera " are formed solely from 

 the coxa3 of the legs. 



In the pleopoda of Phreatoiciis we find several peculiarities which will probably be 

 useful in helping us to trace out the homologies of the pleopoda of other Isopods. All 

 the pleopoda have the basal portion, the " protopodite," present and of moderate size, and 

 in the third, fourth, and fifth pleopoda this bears a fair-sized " cpipodite." The existence 

 of this epipodite is a point of considerable interest. I am not aware of any other case 

 where the epipodite is present in any of the pleopoda of Isopods. In the ' Journal of 

 the Royal Microscopical Society ' for October 1891 (p. 593), in an abstract of a paper by 

 Dr. J. Nusbaum [80] on "The Morphology of Isopodan Feet," it is stated that, according 

 to the author, the epipodite of the thoracic legs has fused Avith the ventral wall of the 

 body-segments. If this should be so in the pcroeon it certainly does not apjiear to be 

 the case with the posterior pleopoda of Fhreatolcus. There is no trace of the epipodite 

 in the first and second pairs of pleopoda, nor can I suggest any reason for its 

 absence. 



Both the exopodite and the endopodite are present in all the pleopoda, both being 

 large flat j^lfites, apparently branchial in function. In all the pleopoda, except the first 

 pair, the exopodite consists of tAvo joints. This character is also possessed by some of the 

 pleopoda of lanthe [16], Mhhiui [27, p. 11], and some allied genera, but the more 

 general rule among the Isopoda is that the exopodite consists of one joint only. In the 

 second pleopoda of the male, although there is a " peiiial filament," the whole pleopod 

 has been very little modified, and it is quite easy to recognize the various parts, and to 

 see that the penial filament is only a specialized portion of the endopodite. In Luithe 

 [16], Ilnnna [27, p. 10], Iclinosoma, and Acaiitlioinnnna [9, p. 40] much further modifi- 

 cation of the pleopod has taken place, and it is not so easy to see the homologies of the 

 various parts. Thus both Bovallius and Beddard consider the large triangular portion 

 which forms the main part of the pleopod to be the protopodite, and Beddard considers 

 the penial filament to be the endopodite, and the exopodite to be represented by a small 

 membranous portion at its base. Whether this is really so, or whether this view AviU 

 require modification, is a question that must be left for future determination ; but this 

 interpretation of the various parts does not appear to harmonize Avell Avith Avhat we find 

 in Phreatoicus. 



SECOND SERIES. — ZOOLOGY, VOL. VI. 27 



