436 THE OCEAN WORLD. 



trilobites were closely allied to the Limulus. Latreille, on the con- 

 trary, classed them near the mollusc, chiton. The tail of Limulus so 

 strikingly resembles that of many Trilobites, that the most common 

 observers may perceive an affinity. 



CRABS AND CEAW-FISH. 



Crabs and lobsters may be regarded as the chiefs or lords of the 

 Crustacean tribes. The crabs have very large claws and smooth 

 backs ; the last have small claws and the back covered with spines. 

 Tiberius Caesar had the face of a poor fisherman scratched by the 

 rugged shell of a craw-fish. 



Lobsters, especially, have an amazing fecundity, and yield an im- 

 mense number of eggs, each female producing from 12,000 to 20,000 

 in the season. The crab is also very prolific. These eggs are, in the 

 lobster, arranged in packets, which are attached to the lower surface 

 of the tail, to which they are connected by a viscous substance. The 

 manner in which the female lobster disposes of her burden is curious 

 and interesting. Whether she bends or stands erect she is able to 

 hold it obscurely or expose it to the light. Sometimes, according to 

 Coste, the eggs are left immovable, or simply submerged ; at others 

 they are subjected to successive washings by gently agitating the 

 false claw which shelters them from right to left. When first exuded 

 from the ovary the eggs are very small, but they seem to increase 

 during the time they are borne about under the tail, and before they 

 are committed to the sand or water they have attained the size of 

 small shot. The evolution of the germ is in progress during six 

 months. At the moment of exclusion the female extends the tail, im- 

 presses upon the eggs an oscillating motion, in order to destroy the 

 shell and scatter the larvae, delivering herself in two or three days of 

 her entire burden (Coste). " As the young lie enclosed within the 

 membrane of the egg," says Couch, " the claws are folded on each 

 other, and the tail is flexed on them as far as the margin of the shield. 

 The dorsal spine is bent backwards, and lies in contact with the dorsal 

 shield, for the young when it escapes from the egg is quite soft ; but 

 it rapidly hardens and solidifies by the deposition of calcareous matter 

 on what may be called its skin." 



As soon as born, the young Crustaceans withdraw from the mother 



