INTERNAL ANATOMY OF INSECTS. 95 



ration, flow without disturbing each other. The excur- 

 rent stream is accelerated in correspondence with the 

 pulsations of the heart ; the recurrent on the contrary 

 being always somewhat more sluggish, and the first to 

 stagnate and cease when the strength of the animal is 

 impaired. In the anterior part of the head currents 

 can be discovered, forming loops like those of the legs, 

 at the roots of the antennae ; each current proceeding 

 from the cranial surface, and in returning taking its 

 course towards the region of the larynx a . 



M. Carus has likewise observed currents of blood in 

 the larvae of water-beetles (Hydrophilus and Dytiscus) b ; 

 but at present he appears to have detected it in no ter- 

 restrial larva. Whether this is occasioned by their opacity, 

 or it exists only in the ovum, as he seems to suspect c , 

 must be left for determination to future observers ; it is 

 scarcely probable, however, that the larvae of Dytisciand 

 Hydrophili should differ from other Coleoptera in their 

 circulation. 



The endeavours of M. Carus to discover any proofs 

 of a circulation in insects in their last state, except in 

 the wings at their first development, were without suc- 

 cess d . He observes that the fact of the currents of 

 fluids in larvae not being defined by vascular parietes, 

 enables us to comprehend the rapidity and facility with 

 which the traces of the circulation are lost in the perfect 

 insect. On the other hand, that the existence of a cir- 

 culation at one period, and its cessation at another, elu- 

 cidate many circumstances connected with the physiology 

 of these animals : for instance, the contrast between the 



a Introd. to Comp. Anat. ii. 396. Engl. Trans. 



b Ibid. 398. Ibid. 399. d Ibid. 398. 



