300 CRUSTACEA. 



This order, according to the system of Linnams, embraces the genus 

 ONISCUS, Linnteus, 



Which is now divided into six sections. Those of the first are parasitical. 

 The subgenera are numerous. Some are aquatic and others terrestrial. Among 

 the latter we have the 



ONISCUS, Linnaeus. 



The true Onisci have eight joints in their lateral antennae, but their base is 

 covered, and the two external appendages of the extremity of the tail are much 

 larger than the others. These animals are vulgarly called Clous-a-porte, and 

 by syncope Cloporte, Porcelets de Saint-Antoine, Wood lice, &c. They inhabit 

 retired and obscure places, cellars, fissures in walls, old buildings, under stones, 

 &c. &c. They feed on decaying vegetable and animal matters, and seldom 

 issue from their retreat, except in rainy weather. They move but slowly, 

 unless they are alarmed. The ova are inclosed in a pectoral pouch. The 

 young, at birth, have one thoracic segment less than the adult, and conse- 

 quently have but twelve feet. 



SECOND GENERAL DIVISION. 



ENTOMOSTRACA. 



UNDER this denomination, which is taken from the Greek, and signifies 

 Insects with shells, Othon Frederick Muller comprises the genus Monnculus of 

 Linnaeus, to which we must add some of his Lernese. 



These animals, mostly microscopic, are all aquatic, and mostly inhabit fresh 

 water. Their feet, the number of which varies, and that sometimes extends to 

 beyond a hundred, are usually fitted for natation only, being sometimes rami- 

 fied or divided, and sometimes furnished with pinnulse or formed of lamella?. 

 Their brain is formed of one or two globules. The heart has always the figure 

 of a long vessel. The branchiae, composed of hairs or setse, single or united, 

 in the form of barbs, combs, or tufts, constitute part of those feet or of a cer- 

 tain number of them, and sometimes of the upper mandibles. Hence the 

 origin of our term Branchiopoda, affixed to these animals, of which at first we 

 formed but a single order. Nearly all of them are provided with a shell com- 

 posed of one or two pieces, very thin, and most generally almost membranous 

 and nearly diaphanous, or at least with a large anterior thoracic segment, 

 frequently confounded with the head, which appears to replace the shell. The 

 teguments are usually rather horny than calcareous, thereby approximating 

 these animals to the Insecta and Arachnides. 



