CLASS INSECTA. 3 



ceed a nuntiber of branches which correspond to the external 

 apertures, or stigmata, for the entrance of air.* 



divisions or chambers of the dorsal vessel, are what Lyonet denominates 

 wings ; and he has also seen the dorsal vessel prolonged as far as the head, 

 and terminated there in the same manner ; but he did not observe the 

 apertures and valvules of which M. Straus has spoken. The definition of 

 the dorsal vessel, given by this naturalist, whatever be the interior compo- 

 sition of this organ, proves evidently that it is not a genuine heart. These 

 observations, moreover, do not teach us what the nature of the fluid is, 

 nor how it is spread through the other parts.of the bodj', so as to minister 

 to their nutrition ; at all events, it is certain, according to the observations 

 of Lyonet, that all the parts of the body, communicate with the corpus 

 adiposum by means of fibrillae. The tracheae throw out branches which 

 extend even into the extremities of the different appendages of the body. 

 It is possible that the action of the air may determine the ascension of 

 the nutritive juices into the interstices, forming a sort of capillary tubes. 



* The number of segments of the myriapodes being undetermined, that 

 of their stigmata is so likewise, and it often exceeds twenty. In the liexa- 

 pode insects it is often eighteen, nine on each side. This calculation, 

 however, is rather founded on the larva than the perfect state of the ani- 

 mal. The caterpillars, the larvse of the coleoptera, and those of a great 

 number of other insects, have one pair of stigmata on the first segment, 

 or that to which is attached the first pair of feet ; the second and third 

 have none, because, as I presume, the development of the wings, which 

 takes place in these rings, renders useless in this place the presence of re- 

 spiratory apertures. The fourth ring, and the seven following, are each 

 provided with a pair; but in the coleoptera in a perfect state, besides the 

 two anterior stigmata concealed in the cavity of the prothorax or corslet, 

 and which are not discernible, we find two others situated between the 

 origin of the elytra and that of the wings : these belong to the mesotho- 

 rax. There are none at the metathorax, unless we consider the two of 

 the first abdominal segment as supplementary ones of the thorax, like what 

 takes place in the hymenoptera with pedicled abdomen, and the diptera, 

 where these two stigmata, with the semi segment on which they depend, 

 form a part of the thorax. Thus, in general, all the hexapode insects 

 have eight pairs of stigmata to the abdomen ; but the last two are fre- 

 quently obliterated In the crickets, the truxales, and the libellulae, the 

 sides of the metathorax are each provided with a stigma— those which 



B 2 



