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XII. On the Mode of breeding of the Qviviviparoits Shark, and on 
the Aeration of the foetal Blood in different Classes of Animals, 
By Everard Home, Esq. F. R. S. 
Read June 7, 1810. 
That some of the shark tribe do not lay their eggs, but 
hatch them within the body, and that others lay them in the 
same manner as the skate, has long been known ; but nothing 
seems to have been accurately made out upon either of these 
subjects, I am therefore induced to lay before the Society the 
following observations. 
In my examination of the squalus maximus, an account of 
which is published, I found that it closely resembled in its in- 
ternal structure, the squalus acanthius of Linn^us, a fish 
common on the Sussex coast, which made me pay particular 
attention to the anatomy of all the parts of this species of dog- 
fish. 
In December, which is the breeding season of this particu- 
lar species of dog-fish, I procured specimens of the male, and 
of the female, in all the different stages of impregnation ; 
from the dissection of these is drawn up the following ac- 
count of the organs of generation. 
The male organs were found in two very different states ; in 
one, the testicles were small, and the penis scarcely discernible; 
in the other, the testicles were larger, the epididymus and vas 
deferens turgid with semen, and the penis put on the ap- 
pearance of a projecting infundibular canal, capable of com 
mdcccx. E e 
