INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 531 



the abclomiual legs or of auy of the future legs of the megalops and 

 crab. In this stage they are very small, much smaller than in the stage 

 figured. After they have increased very much in size, and have molted 

 probably several times, they appear as in the figure just referred to. 

 The termiual segment of the abdomen, seen only in a side-view in the 

 figure, is very broad and divided nearly to the base by a broad sinus, 

 each side the margius project iu long, spiniform, diverging processes, at 

 the base of which the margin of the sinus is armed with six to eight 

 spines on each side. When alive they are translucent, with deposits 

 of dark pigment forming spots at the articulations of the abdomen and 

 a few upon the cephalothorax and its appendages. In this stage they 

 were taken at the surface in Vineyard Sound, in immense numbers, from 

 June 23 to late iu August. They were most abundant iu the early part 

 of July, and appeared in the greatest numbers on calm, sunny days. 



Several zoete of this stage were observed to change directly to the 

 megalops form, (Plate VIII, fig. 38.) Shortly before the change took 

 place they were not quite as active as previously, but still continued to 

 swim about until they appeared to be seized by violent convulsions, and 

 after a moment began to wriggle rapidly out of the old zoea skin, and 

 at once appeared iu the full megalops form. The new integument seems 

 to stiffen at once, for in a very few moments after freeing itself from the 

 old skin the new megalops was~swimming about as actively as the oldest 

 individuals. 



In this megalops stage the animal begins to resemble the adult. 

 The five pairs of cephalothoracic legs are much like those of the adult, 

 and the mouth-organs have assumed nearly their final form. The eyes, 

 however, are still enormous in size, the carapax is elongated and has a 

 slender rostrum and a long spine projecting from the cardiac region far 

 over the posterior border, and the abdomen is carried extended, and is 

 furnished with powerful swimming-legs as in the Macroura. In color 

 and habits they are quite similar to the later stage of the zoeoe from 

 whi(!h they came ; their motions appear, however, to be more regular 

 and not so rapid, although they swim with great facility. In this meg- 

 alo^is the dactyli of the posterior cephalothoracic legs are styliform, and 

 are each furnished at the tip with three peculiar set;e of different lengths 

 and with strongly curved extremities, the longest one simple and about as 

 long as the dactylus itself, while the one next in length is armed along 

 the inner side of the curved extremity with what appear to be miuute 

 teeth, and the shortest one is again simple. 



According to the observations made at Wood's Hole, the young of 

 Cancer Irroratus remain in the megalops stage only a very short time, 

 and at the first molt change to a form very near that of the adult. 

 Notwithstanding this, they occurred in vast numbers, and were taken in 

 the towing-nets in greater quantities even than in the zoea stage. Their 

 time of occurrence seemed nearly simultaneous with that of the zoeae, 

 and the two forms were almost always associated. The exact time any 



