114 M. Blanchard on the Circulation in Insects. 



traverse them in all directions. If we inject an insect by the 

 dorsal vessel, the liquid, after having traversed it in its whole 

 extent, is soon poured into the lacunae of the head and thorax, 

 and is diffused into the abdominal lacunae. It then penetrates 

 between the two tracheal membranes by lacunae which surround 

 the respiratory orifices ; finally it is returned to the dorsal vessel 

 by lateral afferent canals, which extend over the dorsal parts as 

 far as the origin of the tracheal bundles. Thus these afferent 

 canals are equal in number to the stigmata of the abdomen ; it is 

 the same with the number of segments of the dorsal vessel, which 

 also varies according to the types. 



The tracheal tubes, therefore, which convey the air into all 

 parts of the body also carry the re-oxygenated blood to all the 

 organs : the space existing between the two sheaths of the respi- 

 ratory organs appears to perform the office of nutritive vessels. 

 The circulation in insects is effected therefore in the same man- 

 ner as in many invertebrate animals which have a partly lacunar 

 circulation. But there is a very peculiar anatomical disposition : 

 the activity of the circulatory movement here as elsewhere is in 

 relation with the activity of the respiration. 



I have investigated the circulation in a tolerably large number 

 of genera of insects, so as to be assured that there is no essential 

 difference between the different types of the entire group. I am 

 convinced that the anatomical modifications are very trifling, even 

 between the representatives of the different orders of this large 

 class of animals. 



My observations have been made, in the order Coleoptera, 

 principally upon species of Melo'e, Dytiscus, Hydrophilus, Geo- 

 trupes, &c. ; in the Orthoptera, especially upon Blatta ; in the 

 Hymenoptera, upon the Humble Bees, Wasps, and especially on 

 the Bee ; in the Hemiptera, upon Nepa and Ranatra ; several on 

 Lepidoptera and different Caterpillars, and on some Diptera both 

 in the larval and perfect state. 



Throughout I observed the same facts, and I have proved that 

 the larvae and the adult insects do not differ in any but unim- 

 portant relations. 



The facts I have detailed may very soon be verified by merely 

 injecting a coloured liquid through a simple aperture in the 

 abdomen of an insect : in this way all the lacunae are immediately 

 filled, as also the vascular portion of the tracheae, and ultimately 

 the dorsal vessel itself. 



