22 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 



wliifh may each end with a small, blunt si)iiie. Tlie thinl inaxilliped (iig. U) 

 exhibits the typical morphology of this organ in the adult; a somewhat two 

 jointed basal protopodite bears a large five-jointed endopodite of great size, 

 a long slender exoi)odite, a large epipodite and podobrauch; and two arthro- 

 l)ranc'hiie arise from the region connecting the appendage to the body. 



The endoi)odite bears spines upon all its segments and the protopodite has 

 a coni)le of small spines upon its distal segment and a plumose setae upon its 

 proximal segment. The exopodite, in contrast to that of the second maxilliped, 

 has a shorter and more slender basal segment devoid of spines, _ while the 

 second segment has several spines at and near its tip. The lamina of the 

 epipodite has the same characters as in the second maxilliped, Init the plumose 

 set;e along its basal ridge are twice as many. The podobrauch is like that of 

 the second maxilliped. Of the two arthrobranchi:? the anterior one is much 

 like its Jiomologue on the second maxilli2)ed, while the posterior one, nearer the 

 observer in figure 13, is smaller and more simple with fewer lateral filaments. 



Coming next to the ambi;latory api)endages, we find the usual large chela-, 

 the two pairs of slender chelate and two pairs of nou-chelate legs (figs. 14, 15, 

 If). 17, 18). In these appendages of the first larva there are, as in the adults, 

 no exo)iodites, and even the remarkable exoi)odite set* of later larvte and of 

 adults are absent in this first stage, thus adding to the simplicity of the limbs, 

 which is also expressed in the entire absence of plumose set-.v and the itresenee 

 of but few sharp spines. 



The chela (fig. 14) has the recurved terminal hooks first made out by Hux- 

 ley in the English Astacus, and which lead to the firm locking of the ehehp to 

 the egg stalk, as above narrated; and the opposing edges of the claw are ser- 

 rated from the presence of sharp spines pointing toward its tip. The chela 

 bcai-s very large sharp protuberances along the inner edge of the meropodite 

 segment, of no api)arent use, while the great length and thickness of the whole 

 linil) is apparently necessary in that firm holding of the larva to the mother 

 which i-esists the force of the maternal ])leopods that swing the larv:i> liack and 

 forth. 



The ('iMiMxlitc ami gills of the chehi' aiv like those of the third maxilliped. 



Tlic following two legs (figs. 1."), IG) are like one another in every way 

 exce))! in proportion, the first being shorfci- than the second. Each has a 

 sharp claw with sinnes ))ointing toward the tip, but the tips are not recurveil 

 as is the case in the big chehe. The gills on these two appendages are like those 

 ol" the chela, but there is in addition a slender simple gill upon the body wall 

 near the arthrobranchia>. This pleurobrauchia is a single filament with no 

 lateral outgrowths and may be regarded as rudimentary at this stage, as it is 

 also in tlu' adult. 



The remaining legs (figs. 17, IS) have terminal segments almost like those 



