FIDDLER CRAB HYMAN. 451 



The parts of the alimentary canal may be seen, the intestine in 

 active peristalsis. Many of the muscles and much of the nervous 

 system are also visible. 



The only color of the larva is that of the eyes and the pigment 

 spots. The pigment is jet black when fully contracted, but in the 

 expanded condition shows colors ranging from orange through red- 

 brown to olive. The pigment spots have a perfectly definite distri- 

 bution over the bod}\ They may be of considerable help in identi- 

 fying the zoeas of related crabs. For instance, it is very difficult 

 to discover any other easy means of distinguishing the zoeas of 

 fiddler crabs from those of wharf crabs (Sesarma clnerea) or pur- 

 ple marsh crabs (/Sesarma reticulata). They may be distinguished 

 easily and certainly by the fact that those of the fiddlers have a 

 pigment spot at the distal end of the basal segments of the first 

 maxillipeds, while the spot is at the proximal end of the same seg- 

 ment in Sesarma. 



When the zoea is thrown out into the water by the flip of its 

 mother's abdomen, it at once begins to beat its maxillipeds and 

 wabbles up to the surface. It is soon swept out to sea by the tide 

 and begins to feed upon the smaller of its countless companions. 

 For the next four or five days the zoea continues to float in and 

 out with the tide. Occasionally the maxillipeds cease beating and 

 the body slowly sinks, only to be driven back to the surface in a 

 few moments. Jill the time the mouth parts are catching, crush- 

 ing, and swallowing tiny animals and plants. As a result of this 

 feeding the zoea begins to grow. Its inelastic chitin coat soon be- 

 comes too small. A new covering of larger size is formed beneath 

 the old. For a short time now the zoea becomes motionless and 

 sinks toward the bottom. The old coat then splits along the back 

 at the place where the abdomen joins the cephalothorax. The zoea 

 first pushes its body through the slit, and then draws its abdomen 

 and appendages from their old sheaths. This is the first molt. The 

 zoea which emerges is somewhat different from the first hatched 

 zoea and is called the second zoea. The molting period is a perilous 

 time in the life of the zoea. The larva is quite helpless, but fortu- 

 nately it is almost invisible against the sandy or shelly bottom on 

 which the molt generally occurs. 



CHANGES IN THE STRUCTURE OE THE ZOEA. 



The second zoea (figs. 10 and 11) as soon as it is free of the old 

 shell drives upward to the surface again. It is now somewhat 

 larger and stronger and it begins again to feed on its neighbors. 

 The number of swimming hairs on the maxillipeds of the second zoea 

 has been increased to six and so the increased weight of the body 

 can still be maintained at the surface. The large eyes of the zoea 



