THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 55 



When larvae in the second stage were put into Kleienberg's picrosulphuric they 

 flapped their abdomens for some minutes but did not loosen their claws from the 

 pleopod of the mother; when put into alcohol, however, they dropped off, and 

 when into Worcester's liquid they all broke loose and fell to the bottom 

 where they lay kicking their legs for some time as they were not so readily 

 killed as were the third larvae. 



The second larva lives much as did the first larva and in structure is very 

 like it but it differs not only in the above mentioned characteristics of the telson 

 and mode of fixation to the parent but also in the size, proportions, and amount 

 of armament with setse of some of the appendages as will be seen when the 

 nineteen pairs of appendages are taken up in sequence. 



The first antenna (fig. 76) has grown much longer than it was in the first 

 stage (fig. 53), and the basal segment of the exopodite has divided into two so 

 that there are now five in place of four segments. And as the figure shows 

 there are now a few sette upon endopodite, exopodite, and protopodite and of 

 these there are five blunt sensory clubs on the inner face of the exopodite. Two 

 of these are close together on the distal end of the fourth segment, two are close 

 together on the swollen basal half of the fifth and the remaining one stands 

 alone on the narrow terminal half of same segment. The ear is still a 

 simple deep pit without as yet any setae along its edges but with only seven or 

 eight spines or teeth seen with 2 D along its external edge where the second 

 stage of Astacus has plumose setae. 



The second antenna (fig. 77) has greatly grown in length and in perfection 

 of form and as above noted (fig. 69) is no longer carried in the remarkable 

 position it occupied in the first stage (fig. 50). Yet while in a position to be of 

 use as a sense organ the antenna is still markedly lacking in setae : the exopodite 

 scale bears only a row of few spines and the long endopodite bears but a few 

 acicular setae toward its tip. With its increase in length there has been also an 

 increase in number of segments in the filament which has now 36 beyond the 

 three large basal segments in place of the 22 of the first larva. 



The mandible (fig. 78) has added a row of small acicular setee along the 

 medial face of the end segment of the palpus, and developed sharp teeth along 

 the heavy cutting edge of its base. When the palpus is folded down into the hol- 

 lowed face of the mandible two teeth are dorsal and five ventral to the tip of 

 the palpus. 



The first maxilla (fig. 79) has changed but little, but its spines are longer 

 and sharper and it has developed a few, minute, acicular setae. 



This stationary state is still more pronounced in the case of the second 

 maxilla (fig. 80), which has only grown sharp setae in place of the blunt termi- 

 nal spines. The changes in the first maxilliped are also the development of 

 setae in place of spines and the addition of a few setae (fig. 81). 



