265 
whole animal becomes broad and flat, the abdomen being a 
little more than half as wide as the cephalothorax. The two 
eyes and the pair of ocelli on the front edge of the cephalo- 
thorax are distinct; the appendages to the gills appear on 
the two anterior pairs; the legs have increased in length, 
though only a rudimentary spine has appeared on the coxal 
joint, corresponding to the numerous teeth in after life. The 
trilobitic appearance of the embryo is most remarkable. It 
also now closely resembles the Xiphosurian genus Bellinurus. 
The cardiac or median region is convex and prominent. The 
lateral regions are more distinctly marked on the abdomen 
than on the cephalothorax. ‘The six segments of the cepha- 
lothorax can, with care, be distinguished, but the nine abdo- 
minal segments are most clearly demarked, and in fact the 
whole embryo bears a very near resemblance to certain 
genera of Trilobites, as Trinucleus, Asaphus and others. 
In about six weeks from the time the eggs are laid the 
embryo hatehes. It differs chiefly from the previous stage 
in the abdomen being much larger, scarcely less in size than 
the cephalothorax ; in the obliteration of the segments, ex- 
cept where they are faintly indicated on the cardiac region 
of the abdomen ; and the gills are much larger than before. 
‘The abdominal spine is very rudimentary, forming a lobe 
varying in length, but scarcely projecting beyond the edge 
of the abdomen. It forms the ninth segment. The young 
swim briskly up and down the jar, skimming about on their 
backs, by flapping their gills, not bending their bodies. In 
a succeeding moult, which occurs between three and four 
weeks after hatching, the abdomen becomes smaller in pro- 
portion to the cephalothorax, and the abdominal spine is 
prominent, being ensiform, and about three times as long as 
broad. At this and also in the second or succeeding moult, 
which occurs about four weeks after the first moult, the 
young Limulus doubles in size. 
Conclusions.—The eggs are laid in great numbers loose in 
the sand, the male fertilising them after they are dropped. 
This is an exception to the usual mode of oviposition in 
Crustacea; Squilia and a species of Gecarcinus being the 
only exception known to me to the law that the Crustacea 
bear their eggs about with them. Besides the structureless, 
dense, irregularly laminated chorion, there is an inner egg 
membrane composed of rudely hexagonal cells; this mem- 
brane increases in size with the growth of the embryo, the 
chorion splitting and being thrown off during the latter part 
of embyonic life. Unlike the Crustacea generally the primitive 
band is confined to a minute area, and rests on top of the 
