8 CRUSTACEANS. 



CASE, bear considerable resemblance to some insects, and perhaps the 

 family of Oniscidse comes nearest to them of any. They belong 

 to the order Isopoda, or equal-footed crustaceans, which, unlike 

 the crab and lobster with unequal claws, are provided with feet of 

 equal size on each side of the body. The Oniscidse have nu- 

 merous segments and feet, and a number of them possess the 

 faculty of rolling themselves up in a ball like a pill. 



Order ISOPODA. 



Family ONISCIDSE. 



Nos. Oniscus asellus {Linn.). — 1. Specimens (6), (15); 2. Enlarged figure of 

 ditto. 





Oniscus cisellus (rather magnified). Antenna of Oniscus aselius. 



This and its allied species are known as wood-lice or slaters 

 in this country, and sow-bugs in America. They are very com- 

 mon, and may be found under stones or in moist and dark places 

 of concealment. The present species does not roll itself up in a 

 ball, in this respect differing from some of the others. Its external 

 antennse (for, unlike insects, most crustaceans have four antennae, 

 while insects have only two) consist of eight joints, the last elbow 

 of the antennae being divided into three, while the allied genera 

 Porcellio and Armadillo have only seven, the last elbow being 

 divided into two. Like other crustaceans, it carries its eggs in a 

 thoracic pouch, and a whole family of young ones freshly hatched 

 may be found huddled up on the under side of the mother. They 

 are almost omnivorous, and are no doubt of considerable use as 



