THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 29 



Its brilliant color added to its size made it an attractive larva resembling 

 a young lobster after the swimming stages. As indicated in black in the above 

 figures the pigment cells were scattered over the head thorax and abdomen and 

 more sparingly over the chelae, walking legs and basal parts of the antennae. To 

 the naked eye the larva walking on the bottom of a dish seems light flesh-color, 

 translucent and inconspicuous, but the chelae look red, the eyes are dark and 

 the yolk is still a very evident dark, red-black mass of bilobed form across the 

 middle of the head thorax. The liver lobes anterior and posterior to the yolk- 

 were noticeably yellowish and greenish. The abdomen was flesh colored for the 

 most part, but the telson was nearly colorless and with a fringe of white, clear 

 setae so long as to suggest a peacock's tail. On the first abdominal somite the 

 densely crowded pigment formed a conspicuous cross-band (fig. 23). Another 

 such aggregation of pigment was found posterior to the eye and external to 

 the base of the rostrum. In addition to the color due to the much branched 

 red pigment cells, indicated in black in figures 23 and 24, there soon 

 came to be a variable amount of blue color not so readily seen and due to large 

 blue pigment cells. In strong light the red pigment often stood forward on a back- 

 ground of blue. The blue was evident on the basal part of the antenna and 

 antennule, on the mandible and its palp, but not on the maxillipeds. On the 

 dorsal side of both thorax and abdomen there were some blue, faint, scattered 

 areas internal to the red. 



As shown in figures 23 and 24, the cephalothorax in passing from the first 

 to the second stage had become long, narrow, and angular with a long gothic 

 rostrum standing straight out in front between the eyes on a level with the 

 back. The rostrum also had large lateral spines at its base and half way out 

 its length. 



In walking about these larvae carried the antennae and the red chelae for- 

 ward and the abdomen straight out behind as in figure 23, and not bent in 

 under the thorax as in the first stage. However, when not walking the abdo- 

 men was bent as in figure 24. As in a young lobster the slow walking was 

 quickly replaced, at alarm, by rapid backward swimming caused by flapping the 

 abdomen with its extensive telson fan. As the larvae went about more and more 

 away from the parent, they became more individual and more complex in their 

 movements; they were seen to scrape the backs of their heads with their legs, 

 to raise their chelae as if in defense when a shadow passed over them, and in 

 other ways to act like an adult crayfish much more than did the sluggish and 

 simple first larvae. 



In watching one of these second larvae slowly walking, the movements of 

 the five long limbs seemed to be as follows. The fifth, fourth, and third limbs 

 standing out at the sides of the body (fig. 23), were so bent as to hold the 

 body high up above the bottom of the dish and swing back and forth as the 



