BIOLOGY AND STRUCTURE OF HYDROPHILUS CARABOIDES 631 



of Hydro philiis caraboides more thoroughly. The 

 larvae were brought alive into Duboscq's mixture (15 c.c. 

 of 1 per cent, solution of picric acid in 90 per cent, alcohol 

 + 6 c.c. of formalin and 1-5 c.c. of ac. aceticum glaciale), 

 and after they had ceased to move they were cut in two with 

 scissors. 



The fixation lasted from twelve to sixteen hours. After this 

 the larvae were brought througli several portions of 85 per cent, 

 alcohol to wash out the picric acid. Further, they were embedded 

 in paraffin. The sections were stained with iron haematoxylin, 

 Giemsa stain, and Unna's polychrome methylene-blue. 



On the Structure of the Digestive Apparatus. 



The larvae of H . caraboides are distinguished from all 

 other aquatic insects by their unusual way of taking food. 

 Observations on this point have already been made by several 

 naturalists, and Brocher (1913) even figures (semi-diagramma- 

 tically) a larva of H. caraboides taking food (fig. 08). 

 According to a more detailed description of Portier (1911) 

 this process takes place as follows. 



Having caught with its powerful and sharp mandibles its 

 prey (for instance a small crustacean, an insect, &c.), the larva 

 of Hydrophilus ' se dirige vers une plante aquatique ou 

 contre la parol du vase qui la renferme, si aucun objet ne 

 flotte a la surface de I'eau. Au moyen de ses pattes anterieures, 

 elle s'accroche a une asperito quelconque situee au-dessus de 

 la surface, puis elle renverse sa tete en arriere sur son dos. 

 On comprend que, dans cette situation, sa tete emerge com- 

 pletement. C'est, en effet, le resultat auquel la larve semble 

 tendre. ... La proie ayant ete ainsi elevee au-dessus de la 

 surface, on voit I'appareil masticateur entrer en jeu. la chitine 

 est perforee par les tubercules chitineux qui garnissent les 

 mandibules et le sang rouge de la larve de C h i r o n o m u s ^ se 

 met a couler. 



'A ce moment, un flot de liquide noir envahit les organes 



^ Portier describes the feeding of a larva of H . caraboides on a larva 

 Chironom us. 



