92 INTERNAL ANATOMY OF INSECTS. 



lamina somewhat nearer to its abdominal than to its 

 dorsal edge, and running through the greater part of its 

 length suddenly turns and bends its course back towards 

 the body, somewhat nearer to the dorsal than to the ab- 

 dominal margin of the lamina. The channel thus formed 

 in the midst of the granular substance is perfectly trans- 

 parent, except where it is occupied by the blood-globules, 

 or crossed by the bronchiae. The parietes of the channel 

 are not strictly defined, nor formed by any thing like 

 the coats of a vessel, the blood circulating through the 

 granular Parenchyma ,- a circumstance however which is 

 not peculiar to this case, but also occurs generally in the 

 first states of the circulation, as it presents itself for in- 

 stance in the embryo of Pishes, and in thejigura venosa 

 of the incubated egg a . The blood-globules are elongated 

 like a grain of wheat, considerably larger than those of 

 the human blood, and float in a fluid which is invisible 

 because of its transparency, but the existence of which is 

 proved by the variations in the position of the globules 

 in the current, sometimes following its direction, at others 

 crossing it transversely, or more or less obliquely. 



When the animal is vigorous, the current is uninter- 

 rupted, although its velocity is accelerated at regular in- 

 tervals ; and that not only in the excurrent (arterial), but 

 also in the recurrent (venous) part of its course through 

 the lamina. When the animal becomes exhausted, or the 

 laminae exsiccated, the circulation is interrupted, and in 

 the same manner, as under the same circumstances, in 

 the larvae of frogs and lizards; the disturbance displaying 

 itself not merely by a cessation of the process, but also 



a This seems some confirmation of Dr. Virey's opinion, that in- 

 sects in their first states are still a kind of foetus. See above, 

 VOL. III. p. 61-. 



