8 
SPERMATOGENESIS OP NORMAL 
come (2) primary spermatocytes (Fig. 1, scy^), or remain in the 
layer and continue as spermatogonia. The primary sperma¬ 
tocytes, after some interesting changes, divide to form (3) the 
secondary spermatocytes (Fig. 1, scy 2 ), which divide again 
shortly to give rise to (4) the spermatids, through the transfor¬ 
mation of which the spermatozoa are developed. The number 
of chromosomes in each type, as seen at the equator of the 
spindle before division is, in the spermatogonia 16 loops, in 
primary spermatocytes 8 rings or vesicles, and in secondary 
spermatocytes 4 rings or vesicles. It is not improbable that 
the socalled ring chromosomes, at least under certain condi¬ 
tions, are really small vesicles bearing the chromatin in the 
form of an internal shell. To decide this matter has proved the 
most tantalizing point in the whole investigation. Such a ves¬ 
icle could easily take on the appearance of a ring when viewed 
by transmitted light and from the fact that from any point of 
view many of the chromosomes present in a given field appear 
to be rings one is inclined to accept this idea of their vesicular 
nature. On the other hand the chromosomes, of the primary 
spermatocytes at least, undoubtedly originate as rings although 
it is possible for them to become vesicles as they condense. 
What appears to be the elliptical edge of a thick ring is pre¬ 
sented occasionally, and this has decided the writer to use the 
term ring in preference to vesicle, although it should be borne in 
mind that the apparent rings may be vesicles. 
Closely connected with the germinal cells proper are the 
supporting cells or Sertoli cells mentioned above, to which the 
spermatozoa become attached at one period of their transfor¬ 
mation (Fig. 1, s.). They are irregularly disposed among the 
other cells and frequently do not lie in the spermatogonial layer. 
It is difficult to get preparations showing only certain typi¬ 
cal stages, for while certain kinds of cells may be present in 
one view, in another, some of exactly the same phases may 
appear side by side with other cells in entirely different stages 
of development. There seems indeed to be no very definite 
sequence of stages in a given part of a tubule as we find, for 
instance, in the rat. To be more specific, one may find sper¬ 
matogonia, Sertoli cells with spermatozoa attached, and sper¬ 
matids in one view. In another, where the spermatogonia are 
