266 ` THE HORSE FOOT CRAB. 
The figure shows only the upper side, but it has the feet quite 
advanced, and the two great eyes have well begun. In two 
or three days it was considerably changed (PI. 3, Fig. 3). 
Though not so much, still the cephalo-thorax was relatively 
greatly in excess of the abdominal shield. The limbs, though 
not shown in the eut, were quite long, reaching beyond the 
edges of the carapace. The two sessile eyes were now 
prominent, but the central oculiform tubercles, as they have 
been called, but which I prefer to call ocelli, were wanting ; 
for in their place, that is, the central anterior of the cephalic 
shield, was still a depression, or cleft, yet to be filled up in 
the progress of development. To me it seems that so far 
the development was markedly asaphoidal; that is, it re- 
minds me of Asaphus, using that term as the typical genus 
of the Trilobites. Before passing, it should be observed 
that the embryo had its two segments inflected ; and with 
short intervals of rest (not many minutes at a time) kept 
up a very active revolving within its pellucid prison; the 
effect of this friction on the walls of the hollow sphere would 
be to bisect it. As the embryo revolves it lies upon its back. 
August 3d.—Seventy days from the spawning. To-day 
an embryo has left the ovum. It measures two and a half 
lines in length and two lines in width. Except for a little 
space in front the cephalic shield is armed on its perimeter 
by a series of briar-like spines, in two rows of about twenty- 
five each, the spines alternating with some regularity as to 
size. The curved rim of the pygidium, or caudal shield, is 
also fringed, but with setaceous tufts, each tuft being made 
up of hairs of different lengths. This new-born creature is 
in outline almost circular. The cleft in front of the cephalic 
shield has disappeared. The sessile eyes are now promi- 
nent, and are well up on the shield, the two ocelli are quite : 
distinctly marked. But as yet there is nothing of the artic- 
ulated tail that marks the parent Limulus, or its congener 
Eurypterus. 
Such was the form (Pl. 3, Fig. 4) of the little bins be- 
