4:22 J. E. BLOMFIELD. 
the spermatozoon. The interstitial cells still hold the masses 
together. About the middle of August the next stage is 
reached, the hollow vesicle begins to contain developing 
spermatozoa, which appear to be formed by elongation of the 
nucleus to form the head and of the protoplasm to form the 
tail; and when this has progressed some way, so that the 
head is about half its future length, the vesicle splits and 
the spermatoblasts fall back, several in connection with one 
of the superficial nuclei referred to before, on to the wall of 
the crypt, and assume a radial position. After this the only 
further change which takes place is the growth in length of 
the nuclear head till it has attained the size of the mature 
spermatozoon. 
In one section (fig. 31), taken at the right period, a crypt 
will be found to contain vesicles not yet split, others in the 
act of splitting (figs. 36, 37, 38), and the spermatozoa 
arranged more or less radially with reference to a blasto- 
phoral cell, and others again which are in the act of being 
applied to the testicular wall. In this process of sinking 
back on the parietes of the crypt it seems that the intersti- 
tial cells play an important part, from their being connected 
with the fibres forming the wall,as guides to determine the 
application of the bundle to the wall. 
Recapitulation—The history of spermatogenesis in the 
frog is then as follows:—Starting with one of the sper- 
matospores which line the testicular crypts and form the 
testis epithelium, we find that after spawning is over it com- 
mences to grow in preparation for the next year’s stock by 
division of its nucleus. ‘This process continues until there 
is formed a hollow body, spherical when freed from the 
pressure of neighbouring polyplasts, which is the sperm 
polyplast. The exact mode of the formation of this hollow 
sphere I am not able to state. Hach of the spermatoblasts 
of this polyplast becomes a spermatozoon, the tail is formed 
from the plasma by elongation towards the centre of the 
sphere and the head in a similar or perhaps more compli- 
cated fashion. In forming this body all the nuclei are not 
concerned ; certain of them are left behind, superficial to the 
rest, and by proper means can be brought distinctly into 
view. About the end of the summer the spermatoblasts, 
which are very little different from mature spermatozoa, 
arrange themselves in bundles round one of these more 
superficial nuclei, and become with them applied to the wall 
of the testicular crypt, forming a series of bundles arranged 
radially round the wall of the crypt, with their tails 
projecting into the lumen, supported by their heads on the 
