THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 21 



are a few, long hair-like setai standing out from the external face of the pro- 

 to])Oclite. The protopodite has the sau^e two plates seen in the first maxilla 

 (fig. 9), but each is deeply cleft, so that four free tips project toward the 

 mouth. The four tips each bear blunt spines on the outer and distal faces as 

 shown in figure 10, while upon the inner faces toward the mouth they are all set 

 with longer, sharp, curved spines that are claw-like. The eudopodite though 

 longer and more slender than in the firstmaxilla is still very simple and not seg- 

 mented. 



The first maxilliped (fig. 11) shows the protoitodite again reduced to two 

 flat plates much as in the first maxilla (fig. 9), and there are simple spinules 

 on their cutting edges. The endopodite is small and simple, intermediate be- 

 tween that of the second and first maxilla'. In place of the scaphognathite 

 there are two movable parts ; a long flat plate, the epipodite, which is without 

 set* though sparsely spinulous on its posterior edge; and a very long and 

 lirominent exoitodite. The exopodite has a very long swollen basal ])art with 

 very long })lumose seta? on its outer edge as shown in figure 11 and is else- 

 where naked. The terminal part is long, slender and with a very few spines 

 at its tip. As the base of the exopodite lies over the distal end of the epi])odite 

 it is not readily seen that the epipodite has a short truncated extension sug- 

 gesting the anterior end of the scaphognathite as well as the evident posterior 

 blade that reached back into the gill chamber and is comparable to the like 

 portion of the scaphognathite. 



The second maxilla (fig. 12) is more complex; the two segments of the pro- 

 toi)odite are subordinate in mass and extent to the greatly developed eu- 

 dopodite and gill structures, but they bear a few ]ilumose set« u]ion their 

 inner edges. The endopodite resembles that of the first maxilla in position, 

 general form and curvature, but is not only larger but subdivided into five seg- 

 ments and bears spines. In addition to the spines shown in figure 12, there are 

 also long curved ones on the inner face of the terminal segment. Compared 

 with that of the first maxilliped, the exo])odite of the second has a very narrow 

 basal part which is without plumose setai but bears a few long spines on its 

 external edge. The epipodite is present as a long, curved lamina, bilobed at the 

 tip, and along its inner face are borne the numerous blunt filaments of the gill, 

 podobranch. This podobranch is free at its tip, but elsewhere adnate to the 

 lamina and bearing two rows of blunt side ]>a]nlhB or gill filaments which are 

 directed toward the apex, and increase in size in each row from base to apex. 

 The epipodite lamina has a few plumose setae on the rounded ridge at its base 

 and along its edges are scattered curved, short hooks, while its emarginate tip 

 bears a few blunt, fringe-like papillte. In addition to the al)ove gill there is one 

 arthrobranch that is shown in figure 12 to have a long slender stem ending 

 l)luntly and bearing two rows of blunt, cui-ved, finger-like lateral filaments 



