308 Annals Entomological Society of America [Vol. XI, 



sections studied it would appear that tiny secretion vacuoles 

 are formed between the nucleus and the basement membrane, 

 which then migrate around the nucleus so as to lie between it 

 and the striated border, where they fuse to form a large secretion 

 vacuole at the tip, which causes the cell to bulge out, papilla- 

 like, into the lumen of the tube. 



The epithelial cells have a ver}^ delicate but distinct base- 

 ment membrane, besides a nucleated peritoneal sheath which 

 completely surrounds the vessels. 



There is no indication of a lightly staining fibrilla-r area 

 just inside of the basement membrane, as is the case in the cells 

 of the distal portion. 



Distal. The epithelial cells of the distal region of the 

 vessels are larger than those of the proximal region and the 

 striated border is extremely delicate. The cytoplasm stains 

 deeply with eosin, usually a little more intensely than in -the 

 cells of the proximal portion. There is a narrow area of light 

 fibrillar cytoplasm (which even under an oil-immersion lens 

 looks not unlike the striated border) just within the basement 

 membrane which here too, though dehcate, is clearly distinct 

 from the nucleated peritoneum. The rest of the cytoplasm 

 is homogeneous, and stains intensely. There may be few or 

 several vacuolated areas in the cells, just interior to the narrow 

 band of dense cytoplasm, lying just inside the fibrillar area 

 referred to above. 



The nucleoplasm stains a light violet with Delafield's 

 haematoxyhn, while the coarse irregularly scattered, but 

 densely compacted chromatin granules stain deep violet. One 

 or two chromatic granules are usually larger than the others. 

 The oval nuclei are of about the same size as those in the 

 proximal portion. 



Typical. In a typical cross section through one of the vessels 

 of the first series of larval tubes there are four cells, usually 

 not more than one or two of which will be cut through the 

 nuclei. The nuclei are oval, large and central in position. 

 The chromatin granules are large, rather sparse and mostly 

 periferal. 



The lumen is lined by a very narrow hghtly stained striated 

 border of very closely set striae. Between this border and the 

 basement membrane, four areas of cytoplasm may be dis- 

 tinguished, the. last two very narrow^ and the first two of -aboul; 



