BIOLOGY AND STRUCTURE OF HYDROPHILUS CARABOIDES 643 



which develops by karyokinesis of the cells of the cryptae 

 (Rengel, 1898). 



Even in the young larva the intestine for all its shortness 

 forms a loop in the hind part behind the entering point of the 

 Malpighian tubules. In the mature larva the latter are charac- 

 terized by the accumulation of a large number of pigment 

 grains (PI. 27, fig. 5, pg) which concentrate in the basal half 

 of the cells, and surround their nuclei. The parts of the cells 

 which are turned to the lumen of the tubule look in dissection 

 like a broad pale border with a slight indication of a faint 

 striation (the Stabchensaum) without accumulations of pigment. 



It is of interest to compare here the size of the cells of the 

 Malpighian tubules in the young and mature larvae of 

 H. caraboides, drawn under the same conditions (PI. 27, 

 figs. 5, 6). In the young larva the nuclei occupy nearly the 

 whole of the cells, which do not yet contain accumulations of 

 pigments. 



The ileum enlarges nearer to the end of the body into a rectal 

 sac the structure of the walls of the latter being not all alike. 

 The anterior wall of the sac, which borders on the ileum, has the 

 same structure as the latter. It consists of a cylindrical, rather 

 high epithelium, the free surface of which shows a conspicuous 

 striation (PI. 27, fig. 1, ep) ; such a structure of the protoplasm 

 is not an exceptional one ; analogous relations are found for 

 instance in the ileum of the bee (E. Pavlovsky and E. Zarin), 

 the rounded nuclei with minute thickly-crowded grains of 

 chromatin occupying the middle part of the cells or in some 

 places moving nearer to the surface of the epithelium. 



The latter forms on the back of the rectal bladder a thickened 

 disc, the edges of which are strictly defined, as the cylindrical 

 epithelium abruptly passes over into flat epithelium (PI. 27, 

 fig. 1, epp), which is of usual occurrence in the rectal part of the 

 intestine of many insects. 



In the young larva the cylindrical epithelium of the rectal sac 

 (as well as the ileum) is correspoiidingly lower than in the adult 

 larva (PI. 27, fig. 2, ep), a fact which depends chiefly on the degree 

 of growth of the cells, as no secretory processes, which could 



