THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAKUS 21 



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

 topodite. The protopodite has the sanoe 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 endopodite though 

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

 mented. 



The first maxilliped (fig. 11) shows the protopodite 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 maxillae. In place of the scaphognathite 

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

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

 prominent e'xopodite. The exopodite has a very long swollen basal part with 

 very long plumose setas 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 epipodite 

 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- 

 topodite are subordinate in mass and extent to the greatly developed en- 

 dopodite and gill structures, but they bear a few plumose setae upon 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 exopodite of the second has a very narrow 

 basal part which is without plumose set;c 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 papillae 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 setne 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 papillae. In addition to the above gill there is one 

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

 bluntly and bearing two rows of blunt, curved, finger-like lateral filaments 



