DEVELOPMENT, GELASIMUS AFTER HATCHING 489 



weight. After about a week the next molt occurs. The fifth 

 zoea Uves near the bottom Uke the fourth. It is still more dis- 

 proportionately heavy and correspondingly clumsy. During the 

 last day or so of this stage the animal is almost entirely at the 

 mercy of the tide. The next molt occurs at the expiration of a 

 week or ten days. 



WTien the zoea molts to the megalops stage, its mode of life 

 suddenly changes. The animal is now provided with powerful 

 swimming organs, the pleopods, so situated as to be most ef- 

 ficient. Its chelae serve as an excellent means of securing its 

 prey, which now consists, partly at least, of smaller crustaceans. 

 Its organs of equilibration are suddenly well developed and its 

 other sense organs are more nearly perfect. The animal rapidly 

 ascends to the surface and darts swiftly about. The megalops 

 stage probably lasts a long time, and there is only one such stage. 

 Megalopa were kept in the laboratory as long as three weeks be- 

 fore molting to the crab stage. All of those that molted became 

 crabs at the first molt. After swimming about at the surface for 

 three or four weeks, the megalops seeks some protected place, 

 such as the crevices in a rotting board near the shore, and there 

 undergoes the molt to the first crab stage. 



The young crab clings closely to its refuge or crawls about at 

 the water's edge, especially among the exposed roots of sedges. 

 It is very clumsy and very weak. At the end of three days it 

 molts to the second crab stage. Aiter four or five days a second 

 molt occurs. After this molt the little crab runs about quite 

 freely and may dig its first burrow. It now measures about 2 

 mm. across its carapace at its broadest point. Its mode of life 

 from now on is like that of the adult. 



IDENTIFICATION OF THE ZOEAE 



The zoeal forms of Gelasimus may be identified readily. They 

 have prominent anterior and dorsal spines, but have no lateral 

 spines on the carapace. This distinguishes them at once from 

 all the other common zoeae of the Beaufort region, except those 

 of the two species of Sesarma. From these the zoeae of Gelasi- 



