C 2 97 J 
XXIII. The distinguishing characters between the ova of the 
Sepia, and those of the vermes testacea , that live in water, 
explained. By Sir Everard Home, Bart. V P. R. S. 
Read June 5, 1817. 
Linnaeus was led into an error respecting the animal that 
forms the shell argonauta, by the circumstance of a species 
of sepia having been often found in this shell. This erroneous 
opinion has been adopted by many naturalists upon the Con- 
tinent, even those conversant in comparative anatomy. 
Whether the argonauta is really an internal shell, which 
I have asserted it to be, may possibly never be determined by 
direct proofs, as the animal belonging to it has not been met 
with. The present observations are confined to the question 
of the probability of its being formed by the species of sepia 
frequently found in it ; and the materials of the present Paper, 
which are furnished from the specimens of natural history 
collected in the late expedition to the Congo, enable me to 
prove, in contradiction to such an opinion, that the ova of this 
particular species of sepia are not those of an animal of the 
order vermes testacea, that live in water. 
The young of all oviparous animals, while contained in the 
ovum, must have their blood aerated through its coats, but 
in the vermes testacea, if the shell were formed in the ovum, 
the process of aerating the blood, must be very materially 
interfered with, for this reason, the covering or shell of the 
egg first drops off, and the young is hatched before the shell 
of the animal is formed ; this I have seen take place in the eggs 
