320 CHORDATA... 
removing the dorsal peritoneum. Each has a fine duct, the 
ureter, leading from its inner lower border posteriorly to open 
into the urogenital sinus. This sinus opens into the cloaca 
by a small papilla. ; 
As already noted, the male skate has a pair of claspers, 
long firm organs strengthened by cartilages developed in 
connection with the pelvic fins. They are deeply grooved 
and have a large clasper-gland which opens into the groove 
by a duct. 
- Each testis discharges its sperms into its vas deferens 
and thence into the sperm-sac in which they are mixed with 
a secretion ; they then pass out of the cloacal aperture and 
down the clasper-grooves. 
In the female, the ovaries are paired and occupy the 
same position as the testes. They often contain large 
partially ripe ova. The oviducts are paired tubes of large 
size leading the whole length of the abdominal cavity. At 
the anterior end they open by a common aperture zzfo the 
abdominal cavity, and posteriorly each opens into the cloaca. 
The anterior part is called the Fa//opian tube which is thin- 
walled and of small calibre; the posterior part, sometimes 
called the u¢erine portion, is thick-walled and wide; at the 
junction of these two parts isa large ovdducal gland. (There 
is a vestige of the epididymis.) The urinary organs do not 
differ essentially from those of the male. 
The eggs on ripening are shed free into the abdominal 
cavity, and thence pass down the oviducts. They are 
fertilised in the Fallopian tubes and the oviducal gland then 
secretes around them the egg-capsule or purse; they are 
laid singly. through the cloacal aperture. 
If the skate be now turned upon its ventral surface, and 
the skin removed from the head region, as far out as the 
gills and backwards, the following structures can 
ee be recognised (Plate III). In the centre is the 
"cranium, the dorsal cartilaginous wall of which 
may be carefully removed, when it will be seen to possess 
a large central cavity containing the drazm, a pair of anterior 
cavities of the olfactory capsules and a pair of posterior cavi- 
ties, those of the auditory capsules. Between these and the 
olfactory capsules are the eyes. Hence the side of the head 
in the skate bears three pairs of sense-organs, olfactory sacs, 
