4 THE VOYAGE OF H.M.S. CHALLENGER. 



of Spence Bate), aud not the posterior, is the one properly corresponding to the 

 "pleon," its limbs being, in every case, true pleopoda. Moreover, the zoologist who 

 has chosen for his S23ecial study the Cladocera or the Ostracoda, would hardly be inclined 

 to apply the term " pleon " either to the middle or the posterior section, but more likely to 

 the anterior (cephalon), to which are attached the only true swimming limits (antenna;). 



Of the limbs belonging to the middle section of the body, Mr. Spence Bate names 

 the two anterior pairs "gnathopoda." This certainly may be cjuite correct as regards a 

 number of the higher Crustacea, and more especially the Amphipoda, but by no means 

 for all the lower forms, and the term should therefore merely Ije regarded as an ei^ithet 

 for a peculiar modification of those limbs in a few limited groups, precisely as chelipeds, 

 fossorial legs, prehensile legs, &c. 



Even within the restricted group of the Crustacea treated of in the present Report, 

 which belong precisely to the same division (Podophthalmia) as that on which Mr. Spence 

 Bate will report, we find no less than four diff'erent cases in point, not one of which 

 would coincide with the j^roposed terminology. Thus in all known MysidsB, and among 

 the Lophogastridse, at least in the genera Lojjhogaster and Ceratolcpis, only the most 

 anterior pair of these limbs can properly be named "gnathopoda." In the Lophogastrid 

 genus Gnathophausia, too, this pair difi'ers so slightly from the succeeding limbs that, 

 in a strict sense, the term "gnathopoda" even here is very inappropriate. Again, in 

 the Euphausiidfe, not only are all the limbs of this section true legs, but even the last 

 pair of limbs belonging to the anterior section (cephalon) — the maxillipeds — have 

 assumed a perfectly pediform structure. On the other hand, in the genus Eucopia we 

 find, exclusive of the maxillipeds, no less than three of the succeeding pairs of limbs 

 serving as subsidiary organs for mastication, or, more properly, modified as true 

 gnathopoda. 



Moreover, the terms " pleopoda " and "pereiopoda" would not seem to be strictly 

 applicable to all Schizopoda. Thus, the limbs of the posterior division (" pleopoda " of 

 Spence Bate) in all female Mysidte, without exception, aud also in some male forms, are 

 found to be so rudimentary as not to serve in any sense as swimming organs, this 

 function being merely restricted to the outer branches (exopods) of the limbs belonging 

 to the middle section of the body ("pereion" of S2)ence Bate). Nor is generallv the 

 .structure of the true legs in the Schizopoda such as to make them well adapted for the 

 function of walking, or to serve as true pereiopoda ; thus, in the Euphausiidse the delicate 

 structure and very restricted mobility of these limbs make them wholly unfit even to 

 support the body when at the bottom. 



Under such circumstances, I have felt some hesitation in adopting for this group of 

 Crustacea the terminology proposed l)y Mr. Spence Bate, although I fully admit the strict 

 scientific, chnracter and exactness of the terms as regards the greater part of the Podo])h- 

 thalmia. For reasons more fully set forth above, I have deemed it advisable to follow 



