3242 



THE JOINTED ANIMALS 



struction they bring about is due to their habit of boring into timber below water- 

 mark. They are vegetarians, and feed on the wood which they excavate. The 

 members of the group known as fish lice are mostly of large size, the body being 

 longish and oval, and the antennae fixed on the front of the head, which bears in 

 addition two large eyes. The anterior three pairs of thoracic limbs are stout and 

 prehensile, terminating in strong curved claws, while the posterior four pairs are 

 longer and thinner, and adapted for crawling. By means of their powerful fore- 

 feet the Cymothoidce attach themselves to both marine and fresh-water fish, and have 

 a liking for the inside of the mouth of their hosts. 



Another tribe is the Epicaridea, the members of which live parasitically upon 

 other crustaceans. The form of the body in the female is, as a rule, distorted and 

 unsymmetrical; but the smaller males are symmetrical, and are usually found ad- 

 hering to the females. No group of Crustaceans seems exempt from the attacks of 

 these parasites, but it is said that each species has its peculiar kind. 



The best-known example of the tribe Asellota is Aselhis aquaticus, distributed 

 in fresh-water ponds and ditches almost all over Europe. The creature is of a 

 grayish color, mottled with paler markings; and the male, which is longer than the 

 female, measures about half an inch long. The body is long, narrow in front, with 

 a small head, and the antennae of the second pair are about as long as the body and 

 head taken together. The seven segments of the thorax are free and of large size, 

 but those of the abdomen have coalesced into a plate, from the end of which 

 the long slender forked uropods project. The seven thoracic limbs are long, slender, 

 and increase in length from the first to the seventh. 



The tribe Oniscoidea contains the wood lice, in which the abdominal appendages 



are modified for breathing 

 air. Like all crustaceans 

 that have adopted a terres- 

 trial life, they seem able to 

 live only in air saturated 

 with moisture. The body 

 is usually broadly oval, 

 convex above, and flat or 

 hollow beneath, widest in 

 the middle, and gradually 

 narrowing toward the head 

 and tail. The head is 

 small, but the thorax large 

 and seven jointed, the ab- 

 domen being short. Rep- 

 resentatives of this tribe 



are found in all quarters of the globe. A familiar British species is the sea slater 

 (Ligia oceanica), a large species living among the stones and rocks upon the coast 

 above high water. The creature is nocturnal, and unless disturbed is not often 

 seen during the day, but issues from the cracks and clefts of rocks in numbers at 

 night. More obtrusive are the common w r ood lice Porcellio scaber and Oniscus asellus, 



COMMON AND PII,!, WOOD UCE. 



(Natural size.) 



