84 REPORT— 1855. 



prominent lobe, the contents of which are large cells apparently of a secreting 

 kind ; but of the office or use of the organ we have met with no analogy 

 among Crustacea to guide us. 



The Maxilliped. — We here retain the older name in order to distinguish 

 between the two next succeeding members. This is the last of the three 

 appendages which are supported by the same ring. It homologizes with the 

 first or anterior maxilliped in the Macroura, but as an operculum fulfils the 

 duty of the third or posterior, and properly belongs to the cephalic division. 

 The basal joint and the next succeeding are foliaceous in their develop- 

 ment and furnished with hairs ; that of the third joint or ischium is also 

 supplied with small denticles or teeth ; these vary considerably in form, and 

 we think may be used as a valuable adjunct to other circumstances as a test 

 for species (vide PI. XVI, fig. 6, No. 3, and PI. XVII. D, fig. 1 to 5), of which 

 advantage will be taken in the forthcoming history of Sessile-eyed Crustacea. 

 The Gnathopoda*. — The (so-called) thoracic members consist of seven 

 successive pairs, which generally throughout the Amphipoda are developed 

 upon analogous types, and assume to appearance the character of organs 

 more or less perfectly adapted for perambulation. These seven pairs repre- 

 sent three separate forms ; the two anterior, with a few exceptions, are deve- 

 loped into more or less perfect prehensile organs, and homologize with the two 

 posterior pairs of maxillipeds of the higher types of Crustacea, and like them 

 their chief use appears to be as organs attendant upon the mouth. For the 

 sake of distinction from the posterior pairs, we shall adopt the name given 

 to them by M. Milne-Edwards, of gnathopoda, as being singularly appropriate 

 for these subcheliformed organs. 



In swimming, walking or climbing, unless perhaps to overcome any extra- 

 ordinary difficulty, the two gnathopoda are always at rest, being folded up 

 and overlving the external oral appendages. 



Perhaps no member in the whole range of Crustacea in one order under- 

 goes such a variety of modifications adapted to one end, more or less com- 

 plete, as is to be found in the gnathopoda of the Amphipoda. They vary 

 from' the simple finger and thumb of the perfect chela to the rudimentary 

 or obsolete form, in which the hairs that ornament it are more important 

 than the impinging process itself. Sometimes the prehensile character 

 depends upon the dactylos or finger being reflected back and impinging 

 at^ainst the propodos, either of which may have its edge of contact simple 

 or serrated ; sometimes antagonistic to the point there is a minute denticle, 

 a rudiment' of the thumb-like process, which upon full development com- 

 pletes the normal chela of the higher types. The most constant position for 

 this tooth is at the extremity of the anterior inferior angle of the pro- 

 podos, to the portion between which and the articulation of the dactylos, 

 we shall limit the signification of the palm. Occasionally the thumb is the 

 result of an analogous development of the next succeeding joint, the carpus, 

 as we find to be the case with Cerapus and Erichthoneus, or of the still an- 

 terior articulation, the meros, as is the case with ZowcAoweros : in which 

 examples the prehensile claw is formed with one and two intermediate arti- 

 culations existing between the two impinging extremities. 



The first of the gnathopoda is generally the less important of the two, 

 though not invariably, as in the genus Lembos. It is moreover occasionally 

 developed, as in Talitrus and Lysianassa, into a simple foot; a feature that 

 we are not aware is ever the case with the second, which generally is the 

 more important organ of the two. Occasionally, as in Talitrus, Anonyx, 

 Lysianassa, &c., the cheliform character of the second foot is very rudi- 

 * This includes the two first thoracic feet of authon. 



