362 W. HAROLD LEIGH-SHARPE 



pseudosiphon it is not implied that it is homologous, or even 

 physiologically analogous with the siphon proper. As in Raia 

 under similar circumstances, the apopyle exists rather as a 

 region than as an aperture. A flap separates the hypopyle 

 from the opening of the pseudosiphon. Slight vestiges of pseudo- 

 siphons may be seen in some specimens of Scyllium canicula. 



The superficial walls of the siphon sac exhibit purple reticula- 

 tions like the rhipidion, indicating that they are highly vascular. 

 This is one of the reasons why this siphon was chosen for sec- 

 tioning. 



The detailed structure of the wall of the siphon is, in the 

 main, the same as that of Scyllium canicula, and may be taken 

 as a typical example (figs. 3 and 4) . The epithelium is stratified 

 and appears typically to comprise two rows of cells, as in Scyl- 

 lium. Occasionally large mucus-secreting cells, each with a 

 conspicuous nucleus, are seen. These would account for the 

 minute amount of mucilage found in all siphons. These cells 

 are characteristic and do not altogether resemble ordinary goblet 

 cells, such as appear in Rhina. They are, however, well filled 

 with mucus, which displaces the nucleus and cytoplasm to one 

 side and is not stained by the ordinary dyes. Below the epider- 

 mis is a subepidermal layer of connective tissue, extremely rich 

 in blood-vessels (fig. 3) and composed of spindle-shaped cells. 



An acquaintance, who was present at the annual tope-fishing 

 competition at Dover in the summer of 1919, was able to obtain, 

 by imitating the means used by the competitors, some topes 

 which, though maimed, he managed to keep alive for some days 

 in tanks which had been previously prepared for their reception. 

 I was able to inspect these topes which were in a condition of 

 sexual desire. In the absence of females, it was noticed the 

 males attempted to copulate with each other, though one ingen- 

 ious observer considered that they were fighting, and another 

 that they were attempting to relieve each other of copepod 

 clasper and cloacal parasites (Lernaeopoda galei and L. bidis- 

 calis), which, one would think, they could more effectively 

 have done against the rocks, etc., provided at the bottom of 

 the cistern. After the introduction of females, one pair was 



