1716 JOTTINGS FROM THE UNIVERSITY BIOLOGICAL LABORATORY. 
only divided into two lobes. There is a small but distinct mesen- 
tery reflected from the dorsal abdominal wall far forwards where it 
is continuous with the mesogaster, down to the anterior end of the 
large intestine. This contains the mesenteric, splenic and pan- 
creatic arteries, whose highly elastic walls make up a considerable 
part of the substance of the mesentery. The mesogaster is short, 
not extending back on to the stomach itself, but stopping short at 
its cardiac end. The mesorectum has intimately connected with it 
at the sides, in the female the mesoaria, in the male the mesorchia. 
In the brain of Urolophis the only specially noteworthy point 
is the immense relative .size of the cerebellum, the anterior pro- 
longation of which, somewhat unsymmetricaliy developed, overlaps 
not only the optic lobes and the thalamencephalon, but to some 
extent the cerebrum, while the po.sterior covei’s over the whole of 
the medulla oblongata. 
Both Urolophus and Trygon are viviparous. In Urolophus 
testaceus the left oviduct alone is functional. In a pregnant 
specimen there is a large uterine enlargement, the walls of which 
are beset with numerous very long filiform villi richl}’^ supplied 
with blood-vessels. This contains ordinarily only one embryo, 
though in one instance at least I have found tAvo. Of these the 
most remarkable peculiarity in the Selachioid stage, and later when 
the pectoral fins are beginning to resemble those of the Ray — is 
the very great length of the external gills, which are as long as, or 
longer than, the body. They become intertwined with the long 
vascular uterine villi, and it seems not unlikely that their special 
development may be cox-related with the existence of an accessory 
function — that of absoi’bing matter ti-ansuding from the vessels in 
the villi ; since in this as in another viviparous Elasmobranch 
{Pristiophorus cirratus), some of the stages in which I have had 
the opportunity of examining, theie is a marked increase in weight 
discernible Avhen the fully-developed embryo is compared with the 
earlier stages plus the yolk sac. 
* In the liver of Myliobatis, which is likewise two-lobed, there is to be 
observed a curious arrangemeut which I have not noticed elsewhere. This 
is the restriction of any lateral mo\-ement by means of two ligamentous 
bands, one passing from the ventral body wall to the right (larger) lobe of 
liver about the middle of its length, and the other from the lateral wall to 
near the point of insertion of the first. 
