BIOLOGY AND STRUCTURE OF HYDROPHILUS CARABOIDES 645 



in the hind end of the body, which opens into a single l^reathing 

 aperture (a)., The details of the structure and function of 

 this part of the respiratory system are given in Portier's 

 paper, who says of the larvae of H y d r o p h i 1 u s p i c e u s , H . 

 caraboides, and H y d r o b i u s f u s c i p e s , the following : 

 ' II n'y a point de faux stigmates apparents sur les parois 

 laterales du corps, et pas non plus naturellement de 

 ramifications tracheennes qui se rendent a cette region des 



Text-fig. 14. 



trv 



Longitudinal section of ])levu-al appendage of abdomen. The 

 tracheae {tr), muscles (m), fat-body (/6), and cells of haemolj'mph 

 {ch) are visible. Zeiss, ob. DD, oc. 0. 



teguments comme on en voit chez les larves de Dytiscides ' 

 (loc. cit., p. 259). 



This conclusion of Portier's is not precise, at least in the case 

 of the larvae of H. caraboides, as the latter have nine 

 pairs of lateral spiracles, two of which are on the thorax and 

 seven on the abdomen. 



The spiracles have an oval external outline, the latter showing 

 two smaller ovals closely adjoining each other. The spiracles 

 are located on the tops of conical evaginations of the integu- 

 ment, which in these places are covered with dark-brown 

 chitin. These evaginations are situated on the sides of the body 

 in the part of the pleural appendages of the larva (Text-fig. 15, 

 stj). From the spiracles the initial narrow trunks of the tracheae 

 start as a sort of vestibulum. 



They are thick-walled and set inside with a dense brush of 



