1918] Alimentary Canal of Altica Larva 309 



equal width. The first area is composed of more or less reticular 

 cytoplasm which stains deeply with eosin. The second area 

 is made up of lighter staining, homogeneous cytoplasm, sur- 

 rounding secretion vacuoles. The third area is a very narrow 

 band of dense, intensely-stained cytoplasm. The fourth area 

 stains lightly, and is fibrillar, seemingly composed of very 

 fine and closely apposed striations. Outside of this area is 

 the very delicate basement membrane and the whole tube is 

 surrounded by a nucleated peritoneum. 



The aspect of the tubes varies greatly according to the fixing 

 fluid used, and according to the stage of secretion. The 

 differences between the proximal and distal portions of the 

 tubes may be exaggerated in the above account, for they do 

 not always seem to be so well marked, but in all cases which 

 the writer has observed, the cells of the two regions present a 

 different microscopical aspect, and the striated border seems 

 always to be well developed in one and almost wanting in the 

 other. This character agrees with the description of the tubes 

 of Scaur US (Tenebrionidas), by Leger and Hagenmuller (1899), 

 where the proximal end of the vessels is lined with conspicuous 

 ciHa, but no ciHa can be detected in the distal end. 



All of the cells of the "coelomic" portion agree in that they 

 undergo cyclic changes, denoting secretory activity. The 

 cycle is probably the same in all of the cells. While the writer 

 has not made a careful study of the process, it seems to be 

 approximately as follows: The nuclei of the cells at first lie 

 nearer the lumen than the basement membrane; vacuoles are 

 formed between the nucleus and the basement membrane, 

 which pass around the nucleus and lie between it and the 

 striated border; the cell then bulges out, papilla-Hke, into the 

 lumen as these small vacuoles fuse into one large one, which 

 finally discharges its contents into the lumen of the vessel. 



THE COMMON STEM. 



The cells of the common stem formed after the vessels have 

 fused in pairs, as well as those of the common trunk formed by 

 the union of the three vessels, do not differ in appearance from 

 those of the distal region of the vessels, as described above, 

 except that the writer has not been able to detect any trace 

 of the striated border. 



