286 



ZOOLOGY. 



and Europe, which we have called Syncarida, and 

 which have antennae and tails like shrimps, but the body 



Fig. 249. — Gampsonyx Jlmbj-iatus of Eoropean coal measureB, 2^ times natnxal 



and limbs like Amphipods. In the Isopods the body is flat- 

 tened and the head rather broad. 



Fig. 251 is a dorsal Yiew of Serolis Gau- 

 dichaudi Audouin and Edwards, with the 

 two pairs of antennse and pointed sides of 

 each thoracic segment, dissected to show the 

 nervous system, the two pairs of antenna! 

 nerves ; the optic nerves {op) sent to the 

 compound eyes. Fig. 252 represents a trans- 

 verse section of the body, showing the mode 

 of insertion of the legs, and the equality in 

 the tergal and sternal sides of the body. 

 Fig. 254r represents a gill. In the common 

 pill-bug (Porcellio) aerial respiration is per- 

 formed by respiratory cavities situated in 

 the abdomen. In Tylos similar cavities are 

 filled with a multitude of branching coeca, 

 serving for aerial respiration, thus antici- 

 pating the tracheary system of insects. 

 The nervous system is quite simple. (Fig. 

 250, Idotwa, and Fig. 251, that of Serolis.) 

 The digestive canal is straight, consisting 

 of a short cesophagits, a membranous stom- 

 ach, and usually a short tubular intestine ; 

 the liver consisting of several short cceca. 

 In Serolis Gaudicliaudi the stomach is somewhat pear- 



Fig. 250.— Nervons 

 eystem of Idot(Ea zr- 

 »i(»a(a.— Drawn by J. 

 S. Eingsley. 



