DEVELOPMENT, GELASIMUS AFTER HATCHING 499 



1.5 mm. long and 1.9 mm. broad, thus showing a relative broad- 

 ening of the carapace. The lateral borders of the carapace are still 

 lobiilated and beaded, but not so prominently as before. The only 

 changes of note in the appendages are the assumption of adult 

 form by the antenna (fig. 36) and further reduction of the pleo- 

 pods. The antenna is now made up of a large basal segment 

 and a flagellum. The proximal two joints of the flagellum are 

 distinct, but the others are reduced to surface constrictions. 

 The pleopods are distinguishable as minute, shriveled appendages 

 on the second, third, fourth, and fifth abdominal segments, but 

 are absent from the sixth. The abdomen has begun to broaden 

 by the development of lateral flanges. 



The third crab stage (fig. 18). There is no pronounced change at 

 the next molt except in the pleopods. They may be entirely 

 absent in this stage or may be present on the first to the fifth seg- 

 ments as buds so minute as to be indistinguishable under magni- 

 fication less than five hundred diameters. Those on the second 

 segment may be larger than the others. The abdomen has 

 become broader. 



Beginning of sexual differentiation. After the next molt the 

 young crab attains a width of carapace of 3 mm. This stage 

 shows the beginning of sexual differentiation; in males one chela 

 is slightly larger than the other. Abdominal appendages of a 

 second series make their appearance. These develop into the 

 genital appendages of the adult. In male specimens appendages 

 are present as minute buds on the first and second segments. 

 In the female buds are distinguishable with difficulty on all the 

 the segments from the second to the fifth. 



Description of a J^-mm. crab. When the crab reaches a width of 

 4 mm. across the carapace, the sexual differentiation is pro- 

 nounced and other important changes have occurred. The 

 carapace now has the adult shape with straight sides. Numer- 

 ous very brushy hairs have appeared on its anterior surface below 

 the orbits. The abdomen is still further flattened and its segments 

 seem to be more or less completely fused except at their lateral 

 borders. The telson, however, is freely movable, being joined 

 to the rest of the abdomen by a membranous joint. The whole 



