[531] INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 237 
the abdominal legs or of any 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 terminal 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 margins project in 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 25 to late in August. They were most abundant in the early part 
of July, and appeared in the greatest numbers on calm, sunny days. 
Several zoéve 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 zoéa skin, and 
at once appeared in 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 cephalothoracie 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 zoée from 
which they came; their motions appear, however, to be more regular 
and not so rapid, although they swim with great facility. In this meg- 
alops the dactyli of the posterior cephalothoracic legs are styliform, and 
are each furnished at the tip with three peculiar setie 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 minute 
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 zoéa stage. Their 
time of occurrence seemed nearly simultaneous with that of the zoée, 
and the two forms were almost always associated. The exact time any 
