202 Annals Entomological Society of America [Vol. XII, 



The Histology of the Genital Tubes. 



A. VAS deferens. 



From each testis the vas deferens extends caudad to the 

 seminal vesicles. In larval and early pupal stages these 

 efferent ducts are straightish, delicate, almost invisible tubes. 

 They look like very fine transluscent threads leading to the 

 little papilla in the eighth segment, that later becomes the 

 remaining portion of the genital tract. During the larval and 

 early pupal stages, the vas deferens is uniform in diameter and 

 5)ossesses a prominent lumen, which is regular (i. e., without 

 ridges) in its contour. During these stages the cellular structure 

 is represented by Figure 9. The cells are short cylindrical or 

 columnar, possess a rather uniformly staining cytoplasm, 

 and show a prominent central nucleus. The chromatin of 

 these cells occurs in irregular masses, staining prominently. 

 These masses are rather large. The outer covering of the 

 efferent duct may be seen as a fibrous coat that later becomes a 

 layer of circular muscle. 



As the vas deferens grows in length, it becomes convoluted; 

 coincident with its growth in length, there is a corresponding 

 increase in diameter. Cell division takes place very rapidly, 

 during the mid-pupal period. In Figures 10, 11 and 12 we 

 have represented the changes that occur during this time. At 

 first the cells simply grow in length (Fig. 8), becoming tall- 

 cplumnar; the nuclei are still very prominent and the chromatin 

 remains in irregular masses. The cytoplasm begins to become 

 somewhat less dense near the tip of the cells, and begins to show 

 a vacuolated appearance. At first it was thought that this 

 condition was an artifact due to improper fixation. Its con- 

 stancy led to the abandonment of the idea. The outer coat 

 becomes heavier. 



A little later stage will show the conditions represented in 

 Figure 11. Marked changes are beginning. Some of the cells 

 remain stunted or are suppressed in their development. Their 

 neighbors continue to elongate and we have at first a slight 

 irregularity in the contour of the lumen. Parallel with this 

 'change, the cytoplasm becomes definitely vacuolate at the tips 

 of the cells, and a change takes place, in the nucleus. The 

 chromatin begins to break up into smaller particles and these 



