INTERNAL ANATOMY OF INSECTS. 93 
quantity of seemingly superfluous blood remains that is 
not wanted for this purpose. This is expended in the 
production of the caul or epzploon (Corps graisseux 
Reaum.), which laps over and defends all the viscera of 
the animal, and goes principally to the formation of the 
imago*. I have said that Cuvier conceives nutrition in 
insects to take place by zmbzbitzon or immediate absorp- 
tion; that is, I suppose, the different parts and organs 
thus constantly bathed in the blood, imbibe from it the 
particles necessary for their constant accretion. M. Cha- 
brier seems to think that it is the compression and dila- 
tation of the trunk that duly distributes the nutritive 
fluid®; Lyonnet compares the nutrition of insects by 
their fibres from this fluid, when formed into the corps 
graisseux, to that of plants that draw their support by 
their roots from the earth*. Much obscurity, however, 
at present rests upon this subject—much for future inves- 
tigation to explore; but in all the works of the Mosr 
Hiau there is always something inscrutable, something 
beyond the reach of our senses and faculties, which 
teaches us humbly to adore his infinite perfections. 
II. The circulation of the Arachnida is next to be 
considered; and the term applied to these becomes 
strictly proper. Two great tribes, in our view of the 
subject, constitute this Class,—the spiders (Araneide) 
and scorpions (Scorpionide): 1 shall give you some ac- 
count of the circulating vessels of each.—In spzders, the 
heart in general is a long dorsal vessel as in insects, but © 
supposed to be confined to the abdomen, growing slen- 
* Cuv. Anot. Comp. iv. 158. Herold Schmetterl, 28. 
> Sur le Vol des Ins*c. iv. 88. note 1. ¢ Anat. 428. 
