x REPRODUCTION 275 
blastodermie cuticle; when ripe it emerges in the condition 
known as the “Trilobite-larva” (Fig. 158), so called from a 
superficial and misleading resemblance to a Trilobite. They 
are active little larvae, burrowing in the sand like their parents, 
and swimming vigorously about by aid of their leaf-like posterior 
limbs. Sometimes they are taken in tow-nets. After the first 
moult the segments of the meso- and meta-soma, which at first 
had been free, showing affinities with Prestwichia and belinurus 
of Palaeozoic times, become more solidified, while the post-anal 
tail-spine — absent in the Trilobite larva— makes its first 
Fic. 158.—Dorsal and ventral view of the last larval stage (the so-called Trilobite stage) 
of Limulus polyphemus before the appearance of the telson. 1, Liver; 2, median 
eye ; 3, lateral eye; 4, last walking leg; 5, chilaria. (From Kingsley and Takano. ) 
appearance. This increases in size with successive moults. We 
have already noted the late appearance of the external sexual 
characters, the chelate walking appendages only being replaced 
by hooks at the last moult. 
Limulus casts its cuticle several times during the first year— 
Lockwood estimates five or six times between hatching out in 
June and the onset of the cold weather. The cuticle splits along 
a “thin narrow rim” which “runs round the under side of the 
anterior portion of the cephalic shield.”* This extends until it 
reaches that level where the animal is widest. Through this shit 
the body of the king-crab emerges, coming out, not as that of a 
beetle anteriorly and dorsally, but anteriorly and ventrally, in 
1 Lockwood, Amer. Nat. iv., 1870-71, p. 261. 
