250 W. HAROLD LEIGH-SHARPE 
the siphon. ‘This is easily done by closing the cloacal aperture 
by pressure of the finger. The siphon contents-water should 
now be tested and the absence of spermatozoa demonstrated. 
After death a slight pressure on the urogenital sinus is generally 
necessary to cause a flow of spermatozoa. If, now, the ball of 
the pipette be pinched and the stream of water ejected from the 
hypopyle be collected in a glass test-tube just sufficiently large 
to fit well over the tip of the clasper, the microscope will reveal 
the presence of spermatozoa in large numbers, accompanied 
usually by some of the eggs of the nematode that habitually 
infests the alimentary canal of the dogfish. This, I submit, is 
what occurs in nature, the ball of the pipette merely playing the 
part of muscular compression. 
The clasper groove or tube is first filled with spermatozoa by a 
gradual flow through the apopyle. Copulation ensues, and the 
claspers are bent forward so that the apopyle is closed. Mus- 
cular contraction of the siphon wall follows, and the spermatozoa 
are ejected by the flush of sea-water into the oviduct of the 
female. 
The posterior end of the oviduct is naturally dilated to admit 
of the inclusion of the claspers. In young females it is closed by 
a hymen. The rhipidion passes anterior to this dilation, and 
thus forms an organ of closer approximation, subserving another 
function. 
The rhipidion is roughened on its outer border by a group of 
dermal denticles such as are found all over the skin, but pointing 
in the reverse direction. These doubtless serve to prevent 
elision of the claspers from the oviducts of the female and hence - 
function as attaching organs. They are represented by stippling 
in the figure. 
It will be as well to mention in this place that in all the 
figures the stippling indicates the presence of dermal denticles; 
the ‘water-mark’ or ‘moirée’ shading, muscles exposed in dis- 
section; the unshaded portions smooth surfaces, such as the walls 
of the siphon cavity or, especially in the skate, skin devoid of 
denticles. 
