30 DEFINITION OF THE TERM INSECT. 



Digestion. 



Liver and biliary vessels in most replaced by from 

 2 to 4- 150 floating hepatic filaments opening into 

 the space between the two skins of the intestinal 

 canal below the pylorus. 

 Generation. 



Internal organs-. Males — Vasa deferentia, and vesi- 

 culae seminales, and the other ordinary organs. Fe- 

 males — Ovary usually bipartite, with palmate lobes; 

 genital organs single and mostly anal ; one sexual 

 union impregnates the female for her life. 

 Development. In their passage to their adult state, 

 after they have left the egg, insects undergo several si- 

 multaneous changes of their integument or successive 

 moults, and the majority assume three distinct forms, 

 with distinct organs, which appear as rudiments in their 

 second state, and are completely developed in their last. 



In defining the Aracknida I shall only mention those 

 particulars in which they differ from Insectce in their ex- 

 ternal anatomy. 



Class — Arachnida. 

 Body. 



Head and Trunk usually not separated by a suture. 

 Eyes. Two to eight, not lateral. 

 Mandibles cheiiform or unguiculate, representing 

 the interior pair of the antennae of the Crustacea. 

 Palpi pediform or cheiiform. 



Trunk. Legs eight or their representatives : tibiae 

 mostly consisting of two joints. 

 Abdomen with from two to eight spiracles. 



