SEXUAL CHARACTERS — ELASMOBRANCH FISHES 375 



As we approach the body, in III, IV, and V, so as to include 

 some portion of the pelvic fin in the section, masses of glandular 

 tissue appear, at first sporadically around the clasper groove; 

 finally they form a complete investment as in VI. Superficial 

 masses of gland at first appear in III and continue till V, though 

 only indicated for simplicity's sake in IV. The region shown in 

 IV is given in full microscopical detail in figure 11. From IV 

 onward other skeletal supports appear. 



VI, VII, VIII, and IX give various aspects of the gland in 

 transverse section as it narrows anteriorly, and figure 13 is a 

 vertical longitudinal section corresponding to the region IX. 



The gland itself is composed of the usual stratified epi- 

 thelium, in which, quite close together, are numerous goblet- 

 cells of truly colossal dimensions. In the superficial layers of 

 gland there may be as few as one layer of goblet-cells, with 

 smaller cells containing well-marked granules and similar to 

 those of the epithelium between them (fig. 8, C). As the belt 

 of gland increases, so do the numbers of rows of the goblet-cells 

 (figs. 13 and 14). 



These goblet-cells are very much larger than those met with 

 in the colon, etc., of the frog and of mammals, but like them have 

 the cytoplasm and nucleus of the cell pushed to the inner end, 

 almost the whole cell being filled with the unstainable mucous 

 secretion. 



The subject of erectile tissue has already been touched on in 

 Raia in the preceding memoir. In that species I have seen 

 claspers in a state of erection. In figure 11 the tracts of erectile 

 tissue are indicated by the presence of the red blood corpuscles. 

 There is even more erectile tissue in the claspers (fig. 12, I and 

 II), and it will be seen to lie mainly on the side away from the 

 skeletal support. When the gland becomes closed, erectile 

 tissue completely surrounds it (fig. 12, VI and VII). This 

 appears to corroborate what was previously said, under the 

 heading of Lamna, that erection is possibly brought about by a 

 metabolite of the muscle surrounding the gland, as has been 

 supposed to be the case in the human prostate. I may be per- 

 mitted to repeat that erection is most marked in, if not entirely 



