SPERMATOGENESIS IN MYXINE GLUTINOSA. 173 
gradual way in which it divides a cell into two, or a spermato- 
cyte in another animal into a bundle of spermatozoa. Active 
vibration of the tails of the spermatozoa in Myxine usually 
begins only when they have reached their perfect form. 
On the explanation I have adopted the attenuated processes 
of the protoplasmic masses were originally continuous with the 
tails of spermatozoa which have separated. In many cases 
sperm-nuclei are seen in the figures near the bases of these pro- 
cesses, and it might perhaps be argued that the processes are 
the tails belonging to these heads, and that the spermatozoa 
are produced from the spermatocytes tail first as in other ani- 
mals, not head first as I maintain in this case. But it will be 
noticed that in all cases the pointed apex of the sperm-nucleus 
is turned outwards towards the process, while its broad base is 
towards the centre of the mass of protoplasm. Since in the 
perfect spermatozoon the tail is attached to the base of the 
sperm-nucleus, and not to the apex, it follows that my account 
of their formation is correct. 
I have to complete the history I read from the appearances 
by saying that the spherical nucleated spermatocytes give rise 
to the protoplasmic masses containing sperm-nuclei. The 
single nucleus of a spermatocyte doubtless divides into several 
sperm-nuclei, producing structures like that shown in fig. 1, ec. 
It must be mentioned that the bipolar spindles, of which an 
example is represented at a, fig. 2, are in most specimens of 
Myxine, next to the spermatozoa, the most abundant elements, 
multipolar cells being comparatively rare. These spindles vary 
very much in size, and in many of them neither sperm-nuclei 
nor nuclei of any kind can be detected in them in the fresh 
condition. The explanation of these facts is, I think, that as a 
rule the sperm-nuclei pass out successively in the same 
direction, and so leave only two processes behind them. This 
view is clearly supported by the condition of many of the 
spermatocytes represented in figs. 1, 2, and 3, where a sperm- 
nucleus is seen at the base of a process which was formed by 
the production of a spermatozoon already separated. 
I will now give the results I have obtained from the study 
