SPERMATOGENESIS IN MYXINE GLUTINOSA. 175 
6 and g shows that the explanation I have given of the forma- 
tion of the spermatozoa is correct: the sperm-nucleus in g is 
evidently about to separate from the spindle, so as to pass first 
into the condition of 4, and finally to become the head of a 
spermatozoon. The nucleus in ¢ may be one which would 
afterwards have formed a sperm-nucleus, but it is possible that 
the whole of the chromatin of a spermatocyte is not always 
used up in the formation of sperm-nuclei, and that the nucleus 
in ¢ is a portion left in the spindle which would remain there 
unused. In da portion has remained behind and resumed the 
structure of an ordinary nucleus. In any case chromatin is 
sometimes present in the spindles, sometimes not. The struc- 
ture shown at f is a rounded mass of protoplasm connected by 
a filamentous process with a spermatozoon-head of unusually 
large size, the sperm-nucleus consisting of discontinuous 
chromatin. In some capsules numbers of spermatozoa have 
heads of this structure, from which it may be concluded that 
the degree of concentration of the chromatin in the sperm- 
nuclei at their first formation is somewhat variable. In all 
probability when the chromatin of the sperm-nucleus is at first 
reticulated, it concentrates afterwards into the solid mass of 
smaller dimensions which is characteristic of the head of the 
ripe spermatozoon. 
Pl. IV, figs. 7 and 8, represent cells with nuclei in the 
resting state, from the same capsule as the elements shown in 
fig. 9. Some of these cells are as large as the spermatocytes 
of an unripe capsule, others are somewhat smaller, but probably 
all are spermatocytes which have not yet begun to produce 
spermatozoa. 
Fig. 11 shows elements from a ripe capsule from another 
specimen. The three spindles here containing several sperm- 
nuclei agree in all respects with similar elements which were 
described above in fresh preparations. They prove conclusively 
that my interpretation of the elements as seen in the fresh 
condition was correct ; the correspondence between the sperm- 
nuclei in these spindles and in the heads of spermatozoa is 
exact, Moreover it is clear from the condition of 6 and c that 
