REPRODUCTION 



275 



blastodermic 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. I'hey 

 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 Prestiuichia and Belinurus 

 of Palaeozoic times, become more solidified, while the post-anal 

 tail-spine — absent in the Trilobite larva — makes its first 

 2 1 



Fig. 158. — Dorsal and ventral view of the last larval stage (the so-called Trilobite stage) 

 of Limul-us 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 slit 

 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. 



