SEXUAL CHARACTERS—ELASMOBRANCH FISHES 259 
The posterior end of the skeleton of the clasper (myxaptery- 
gium) is provided with a basal joint which is capable of causing 
in the tip of the whole clasper a flexion inward, as is shown In 
the inset to the right in figure 2. This no doubt forms a means 
of attachment during copulation and is found developed in 
Mustelus to a greater degree, as will subsequently be shown. 
ACANTHIAS VULGARIS 
The spurred or spiny dogfish, or piked or picked dog 
This siphon, for so large an animal, is small as compared with 
that of Scyllium, and situated more immediately beneath the 
skin in a space filled with loosely packed connective tissue, 
otherwise it presents no differences. In the accessory clasper 
structures this species exhibits the most striking divergences 
from Seylliium, as shown in figure 8, in which the relations 
between the various structures are indicated in two positions. 
Six specimens taken at Plymouth in May, 1918, were exam- 
ined the day or so after they were caught. No copepod para- 
sites of any kind were observed upon them. 
The apopyle is considerably removed from the cloaca. The 
actually closed portion of the clasper tube is short. The rhi- 
pidion is pronounced, but this type is chiefly remarkable for 
the presence of a short straight thorn-like spur, a brief distance 
anterior to the hypopyle. The spur is worked by a powerful 
muscle, so that while it normally is kept in a relaxed condition 
against the side of the clasper, once the latter has entered the 
oviduct of the female it can be erected, thus forming an impor- 
tant organ of attachment, penetrating, and even lacerating the 
tissues of its partner. 
The extreme tip of the clasper, posterior to the hypopyle is 
also provided with a very small much-curved claw, which is 
likewise movable. It is difficult to see what attaching function 
this can possess. Possibly it may serve to rupture the hymen. 
This animal is provided internally with short globular sperm 
sacs instead of elongated thin ones as in Seyllium. 
JOURNAL OF MORPHOLOGY, VOL. 34, NO. 2 
