SEXUAL CHARACTERS—ELASMOBRANCH FISHES 249 
dilute formalin), was discharged by squeezing the ball and the 
carmine injected into the siphon sac. 
The undissected side of the specimen now became most dis- 
tinctly dilated on the abdomen to a surprising degree, causing 
a bulging of the skin in that locality, proving that the injection 
fluid was actually entering the siphon, as indicated on the 
(observer’s) right-hand side (fig. 1). 
The pipette was now quickly withdrawn and the clasper bent 
smartly forward. In this position the apopyle is closed. Since 
the copulation of elasmobranchs takes place ‘head to head’ (a 
point for consideration in a later memoir dealing with the fe- 
male), it is obvious that in nature the claspers of the male are 
always thus bent forward in copula. I imitated the natural 
angle as much as possible. 
I next pressed lightly upon the distended siphon with a finger, 
simulating in this the natural muscular contraction of the living 
animal (an assistant having loosely ligatured the organ proximal 
to the apopyle). The carmine injecting fluid forthwith spurted 
out voluminously from the hypopyle to a distance of 3 or 4 
feet, while none oozed out at the apopyle, though obviously 
not hampered by the presence of the ligature. Indeed, the 
presence of the ligature is not necessary to the success of the 
experiment. On repeating the experiment more slowly, it was 
easily demonstrated that a spiral rotatory motion was given to 
the ejected fluid by the presence of the rhipidion which is not 
very well developed in this species, though more so than in 
S. canicula; conversely, if the rhipidion be removed by dissec- 
tion the fluid is not so rotated. 
In order to simulate natural conditions as much as possible in 
the next experiment, the point of the pipette was inserted 
through the wall of the anterior end of the siphon sac and liga- 
tured so as to preclude any possibility of leakage, and the whole 
fish immersed in a tank of water. It must be remembered that 
in life the siphon does not require to be filled as in the preceding 
experiment, since it normally contains sea-water. 
To make conditions equal, precautions must be observed that 
escaping spermatozoa from the cloaca are not now drawn into 
