6 
DR. C. H. JONES ON THE STRUCTURE, DEVELOPMENT 
not any biliary deposits were seen. The gall-bladder was very full of bile. The ducts 
dissected out appeared occasionally distended, but to a much less extent than in the 
preceding instance ; the epithelium in the larger ones consisted of columnar particles, 
which viewed in situ gave a mosaic or pavement-like appearance ; in those of next 
size the epithelium was in great part vesicular ; and in those of smallest size it chiefly 
consisted of nuclei and amorphous matter, with a few incipient vesicles. In several 
of the ducts the canal was very much narrowed by the epithelial growth. 
These details, though rather minute, are not, I think, devoid of interest, especially 
as illustrating the actively growing nature of the epithelium of the ducts. With 
regard to the condition of the parenchyma generally I have nothing to add to my 
former observations, except that I have usually noticed that when the ova are con- 
siderably developed, and form large masses occupying a great space in the abdomen, 
the quantity of oil in the liver is greatly diminished ; it seems to be diverted from its 
usual place of deposit, and appropriated to the formation of the growing structures. 
Development in Fishes. 
I now proceed to describe the development of the liver in this class, in which it is 
observed under very favourable circumstances, as the stages succeed each other 
slowly, and the transparency of the tissues enables the observer to conduct his 
examination with little injury to the specimen. In a young Perch {Perea Jluviatilis) , 
which had recently quitted the ovum, and in which the circulation was distinctly 
visible, I found the vitelline sac attached to the body, but not included by abdominal 
walls ; there was no intestine yet formed, nor any trace of liver. In the vitelline sac 
there was seen a smaller one lying near the anterior extremity just behind the heart; 
this contained a more highly refracting matter than that in the larger vitelline cavity. 
The next day I observed that the heart was covered in by a strong membrane which 
passed over the yolk-sac, and was continuous with the inferior vertical fin, and 
doubtless with the sides of the body, thus closing in the abdominal cavity. 
An intestinal tube was now formed, and an oral cavity, but the intestine did not 
communicate with it, nor had it any anal outlet. By the morning of the next day 
the intestine had extended quite to the throat, and was enlarged into a fusiform dila- 
tation corresponding to the stomach, while a narrow space intervened between it and 
the vertebral column. By the evening of the same day the continuity of the intestine 
as oesophagus into the throat, and the cavity of the mouth was most distinct. I 
observed a short blind offset passing backwards and upwards towards the vertebral 
column from the stomachal dilatation ; this was evidently the rudiment of the air- 
bladder. A day later the plicae of the intestine had begun to appear ; its walls were 
very thick, there was no trace to be seen of liver, or of renal glands. Peristaltic 
movements were observed in the intestine twenty-four hours later ; the duet of the 
air-bladder was now of pretty good length, but scarcely appeared to be hollow. 
Two days from this time the intestine was sufficiently consistent to admit of being 
detached ; its surface was still more plicated ; its posterior fourth was separated from 
