DEVELOPMENT, GELASTMUS AFTER HATCHING 497 



The changes in the maxilhpeds are profound (figs. 68, 70, and 

 74). The first and second pairs are transformed from swimming 

 organs and all three pairs become functional as mouth parts. 

 The first and third pairs bear well-developed epipodites, and each 

 of the second pair bears a tiny bud on its lateral surface — the be- 

 ginning of an epipodite and a gill. In all these appendages the 

 proximal segment of the exopodite is elongated and slender, while 

 the distal segment is small and is carried at right angles to the 

 basal segment. It bears three or four weak, slender, plumose 

 hairs. The endopodite of the first pair is twisted so that the 

 lateral edge of its distal portion becomes median. It bears only 

 a few small hairs. The endopodites of the second and third pairs 

 are composed of four segments, are stout, and bear numerous 

 macerating spines. 



The gills of the megalops are four on each side — a pleurobranch 

 between the third maxilliped and the cheliped, two podobranchs 

 on the cheliped, and one podobranch on the second periopod. 



The chelipeds are large and functional as pincers. The sec- 

 ond, third, and fourth periopods are long and slender with some- 

 what hooked extremities. They may be used in crawling, but 

 are used chiefly for clinging to some protecting cover. The fifth 

 periopod seems to be useless. It is small and has several long 

 hairs at its tip, and is carried folded over the back of the carapace. 



The pleopods (fig. 79) are large, well-developed swimming or- 

 gans. Each is composed of a basal segment bearing an exopodite 

 and an endopodite. The exopodite is a flattened lobe bearing 

 from seven to fourteen swimming hairs around its border. The 

 endopodite (fig. 81) is small, bears no hairs, but has three shriv- 

 eled, curled processes at its tip which may represent atrophied 

 hairs. 



The first crab stage (fig. 16). When the megalops molts to the 

 first crab stage, the cephalothorax is slightly altered, becoming 

 broader and more depressed. The abdomen shows a great 

 change. It is permanently flexed under the thorax into a groove 

 in which it fits, and its appendages, the pleopods, are shriveled 

 and hidden under it. 



