628 THE AMERICAN NATURALIST. Vor. XXXIX. 
developed ovary, with eggs in the process of yolk development. 
In regard to the age at which these changes take place, we have 
as yet no definite information. As is already known, the proc- 
ess of development within the egg is slow, when compared with 
the rate of growth of other vertebrate embryos ; and their post- 
embryonic growth is probably also very slow, for very small fish 
(viz. thirteen or fourteen inches long) kept in the aquarium for 
three months, showed at the end of that time no perceptible 
change in form or size, although they fed in a normal way, or 
at least, as normally as any other fish in the aquarium. 
One of the most interesting points about Bdellostoma, because 
of its supposed taxonomic value, is the variation in the number 
of gills. Taking the number found in the hagfish of different 
geographic regions as a basis, the Bdellostomids have been 
divided not only into different species, but also into different 
genera, Bdellostoma forsteri, of the Cape of Good Hope, with 
its six to seven gills on each side being placed in one genus, and 
the Bdellostomas of the American Pacific coast in another, sub- 
divided into two species, Bdellostoma dombeyi, with ten gill slits, 
found in Chilean waters, and Bdellostoma stouti, whose usual 
number of gill slits is eleven or twelve, in the waters of Cali- 
fornia. Dr. Ayers ('94), after a careful comparison of the Cape 
of Good Hope and California varieties, concluded that there was 
no specific, far less generic difference between the two forms, 
and stated that they, together with the Chilean variety, belonged 
to one species, the preferable name for which was Bde/lostoma 
dombeyi. This conclusion was scouted by Howes (94), but 
purely on a priori grounds, and without any study of the forms 
in question. Since this time not much work has been done that 
would throw light on this question until within the last year or 
two, when Dean, studying the hagfish found off the coast of 
Japan, came across a variety that he called Homea okinoseana, 
distinguished by having eight gills on each side, but in all other 
respects like the hagfish of other localities. This Japanese 
variety thus fills in the gap between the Cape form with its six 
to seven gills, and that of Chile, with ten gills on each side. 
It is worth while to study the California form carefully and in 
detail with regard to the gils. Dr. C. H. Gilbert of Stanford 
