30 DEFINITION OF THE TERM INSECT. 
DIGESTION. ; 
Liver and biliary vessels in most replaced by from 
2 to + 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- 
culze 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 Arachnida I shall only mention those 
particulars in which they differ from Jnsecta in their ex- 
ternal anatomy. 
Class—ARACHNIDA. 
Bopy. 
Heap and Trunk usually not separated by a suture. 
Eyes. ‘Two toeight, not lateral. 
Mandibles cheliform or unguiculate, representing the 
interior pair of the antennze of the Crustacea ? 
Palpi pediform or cheliform. 
Trunk. Legs eight or their representatives : tibiee 
mostly consisting of two joints. 
ABDOMEN with from two to eight spiracles. 
