4o Cincinnati Society of Natural History. 
tion between the efferent branchials, carotids, and dorsal 
aorta, as I found it, in five specimens of Bdel/lostoma TOS 
taken entirely at random. 
The variations apparently have no constant relation to the 
size or sex of the specimen. ‘The number of efferent vessels, 
of course, varies with the number of gills. 
F, G, H, I, J. Diagrams of the efferent branchial arteries and their connections 
(dorsal view) in Bdellostoma dombeyi. Lettering same as in plate figures (q. v.) 
As a result of his studies of the blood vessels of Chlamydo- 
selachus, Dr. Ayers (Morphology of the Carotids, Bul. 
Museum. Comp. Zool., Harvard. Vol. XVII, No. 5, p. 211), 
reaches the following conclusion: ‘It is likewise obvious 
that the carotid vessels cannot strictly be said to arise from, 
or constitute the remains of, any particular pair of aortic 
arches, but represents all that is left of the commissural 
trunk from the most anterior arch of the ancestral form to 
the most anterior arch of any existing form.’’ Bdellostoma 
and the Myxinoid type would seem to indicate rather the |. 
origin of the carotid arteries from a longitudinal trunk con- 
necting a// the efferent branchial vessels on each side. 
I have not as yet been able to work out fully the distribu- 
tion and homologies of the blood vessels in the head region. 
This problem, on account of its diffictilty and importance, is 
reserved for a special paper. I may mention, however, that 
28 
