CKUSTACEA OF NEW ZEALAND. 203 



so-called " cpimera " are really the coxne of the legs, Stcbbing [108, p. 289] appears 

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

 Phreatoicus, in the segments of the pleon the pleural portion of the body-ring has 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 sutiu'e or line of division. 

 The same tiling is of course true of the pleon of most Amphipoda. Tims these true 

 outgrowths of the body-ring oppear 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 cox0e of the legs. 



In the pleopoda of Phreatoicus we find several peculiarities wliich 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 " epipodite." 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 Isopodau Teet," it is stated that, according 

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

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

 the case with the posterior pleopoda of Phreatoicus. 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 plates, apparently branchial in function. In all the pleopoda, except the first 

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

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

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

 second pleopoda of the male, although there is a " penial 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 filanient is only a specialized portion of the endopodite. In lanthe 

 [16], Munna [27, p. 10], Ichnosoma, and Acanthomunna [9, p. 46] 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 will 

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

 interpretation of the various parts does not appear to harmonize well with what we find 

 in Phreatoicus. 



SECOND SERIES. — ZOOLOGY, VOL. VI. 27 



