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 antennas ; each current proceeding 
from the cranial surface, rmd 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 Dytisci and 
Hydrophili should differ from other Coleopcra 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 Comjt. Anat. ii. 396 — . Engl. Trans. 
b Ibid. 398. c Ibid. 399. A Ibid. 398. 
