FIDDLER CRAB- — HYMAN. 455 



similar structures on the basal segments of the appendage these act 

 as mouth parts for holding the food and passing it up to the mandi- 

 bles. The third maxillipeds (fig. 26) have undergone a wonderful 

 growth. They are now by far the largest and most powerful of the 

 three pairs of maxillipeds. With these changes in structure and 

 functions the maxillipeds reach practically their adult condition. 

 Their further development consists mostly of increase in size and 

 power and the development of their hairs as organs to aid in eating. 

 The six pairs of appendages that form the mouth parts of the 

 megalops are practically the same in structure as those of the adult. 



The greatest change in the transformation from zoea to megalops 

 occurs in that region of the body that carries the pereiopods or 

 walking legs. This region now becomes the largest part of the 

 body and is considerably larger than the head region. All of the 

 pereiopods are well developed and each has practically its adult 

 condition except the fifth. The pincers are large and are well 

 developed. They form effective organs of offense, and the megalops 

 does not swim along the surface and trust to luck to send a few 

 diatoms or protozoa to the spiny basket of its mouth parts. It can 

 see well and swim swiftly. It singles out its prey and pursues it. 

 The food of the megalops consists of any animal small enough for 

 it to cope with successfully. Other smaller Crustacea come within 

 this category and many a luckless zoea of its own race falls a prey 

 to the fierce cannibalism of the megalops. The prey is caught and 

 crushed in the pincers and passed back into the grasp of the mouth 

 parts. These prepare it for swallowing. The prey is not bitten 

 into pieces but rather is mashed until it can be crammed whole into 

 the mouth opening. The second, third, and fourth pairs of pereio- 

 pods are well developed, but are seldom of use to the megalops at 

 this time. The} 7 are carried folded in swimming but enable the 

 larvae to cling very tenaciously when it comes to rest on some 

 floating bit of seaweed or bark or when on some rare occasion it 

 has the good fortune to find a bit of decaying meat. The fifth pair 

 of pereiopods are peculiar. Instead of ending in pincers or needle 

 points for clinging they end in a tuft of long hairs and the append- 

 ages are carried folded up over the back. They seem to be of no 

 use to the megalops. In their position they recall the fifth pereio- 

 pods of those peculiar crabs that use these appendages for cling- 

 ing to protecting shells like the clam-shell crab (Ilypoconcha), 

 or those forms that cling to sponges or sea weeds like the red sponge 

 crab {Dromidia antiUen-sis) . The gills of the megalops are borne at 

 the base of some of the pereiopods. 



The abdomen is the distinctive feature of the megalops. It is not 

 like that of either the zoea or the crab. The appendages of the abdo- 

 men are now the organs of locomotion. On each of its six segments, 



