182 J. T. CUNNINGHAM. 
It seems to me that spermatogenesis in Myxine resembles 
that which occurs in certain Invertebrates more closely than 
that which occurs in the higher Vertebrates. In Chztopods 
and Molluscs, e.g. in the earthworm and Helix, according to 
Blomfield’s description (5 and 6), a large cell (spermatospore 
or spermatogonium) undergoes a process of division which 
leads to the formation of a number of small round cells (sper- 
matoblasts) surrounding a larger central mass of protoplasm, 
the blastophore. Each of the spermatoblasts in these cases 
becomes a single spermatozoon, while the blastophore has only 
a subsidiary supporting function, and, after the spermatozoa 
have separated from it, degenerates. Moreover, in the trans- 
formation of spermatoblast into spermatozoon, the tail appears 
first, projecting away from the blastophore, and the nucleus of 
the spermatoblast does not acquire the characters of the head 
of the spermatozoon till after the tail has begun to appear. 
In the testis of Myxine I can only compare the spindle-shaped 
body, from which the spermatozoa separate, with the blasto- 
phore of Cheetopods and Molluscs ; and the striking peculiarity 
is, as I pointed out in my first description, that the sperma- 
tozoa in Myxine are, when first differentiated, attached to the 
blastophore by their tails, and not by their heads, as in Che- 
topods and Molluscs. This peculiarity is connected with 
another, namely, that the heads of the spermatozoa, or sperm- 
nuclei, as I have called them, are in Myxine fully differentiated 
within the undivided spermatocyte (spermatospore, Blomfield) 
before any differentiation of the tails has taken place ; whereas, 
in all other cases described, a partial or complete separation of 
spermatoblasts or spermatides takes place first, and the nuclei 
of these only subsequently acquire the characters of sperm- 
nuclei. The only process at all similar to that which I have 
described in Myxine, so far as I can discover, is one described 
by Jensen (4) in the Molluse Triopa clavigera. According 
to this description, young spermatogemmee consist of a small 
number of cells all similar, and forming morulz adjacent to 
the wall of the tubule of the testis. The cells multiply by 
indirect division until their number is considerable, Then a 
