636 CIRCULATION OF THE BLOOD AND DORSAL VESSEL. 



understood the function of the dorsal vessel, Cuvier denied the 

 existence of a circulation in Insects. C. G. Carus [307] made 

 many observations on this phenomenon, and clearly established 

 the fact that not only the blood circulates, but in many Insects, 

 perhaps in all, the course of the haemal fluid is circumscribed 

 by very definite channels. 



Indeed, long before, Baker [306] in 1755 described not only 

 the pulsations of the dorsal vessel, but observed the blood 

 flowing in very definite channels in the wing of a species of 

 Locust ; and in 1837 Bowerbank [310] gave a detailed account 

 of the circulation in the wings of Chrysopa perla. He describes 

 the blood current as flowing steadily through all the nervures 

 towards the apex of the wing, and as returning by a single 

 channel, running in the posterior margin of the wing, in a 

 more rapid stream, to the thorax. 



Definite Course of the Blood in the Appendages. Verloren tried 

 to account for the circulation in the wings and legs by the 

 supposed existence of small accessory hearts, similar to lymph 

 hearts, in each appendage, but he had no evidence to offer in 

 favour of the view, and to this clay no such hearts have been 

 discovered. In aquatic larvae the circulation in the leaf-like 

 gills and in the anal setae is most rapid, and it is altogether 

 similar to that in the legs, wings and elytra of perfect insects. 

 In the former, lymph hearts could not fail to be seen if they 

 existed. 



The great cavitioe of the body of the imaginal insect are 

 divided from each other by narrowings, the small openings in 

 the diaphragmata, and the narrow abdominal pedicle of the 

 \Vusp, for example ; and not only transverse, but longitudinal 

 more or less complete septa traverse the body. Similar 

 septa also exist in the appendages. Thus the blood flows 

 into the head above the tentorium, and leaves it below 

 the tentorium ; and the circulation through the proboscis is 

 provided for by blood sinuses on its dorsal surface which 

 communicate with the region above the tentorium, and 

 on its ventral surface with the region below it ; these 

 intercommunicate by narrow channels offering considerable 



