26 
Fridtjof Nansen. 
[No. 7. 
objects, in proof that the follicular epithelium does not directly 
produce, or contribute to, the formation of spermatozoa ; these are 
exclusively derived from the spermatocytes. 
The development of the spermatozoa from the spermatogons seems 
to be very easy to trace out in Myxine, and I think, therefore, 
that this animal offers excellent material for investigations on sper- 
matogenesis. 
From what I have seen, I think it to be most probable that 
in the first stage, in the quite young male organ, each testicular 
capsule, consists of one large cell, spermatogon, with a very large 
nucleus, and surrounded by a follicular epithelium. This young 
testicular capsule is, thus, in its structure quite similar to the young 
ovum with its epithelium ; I have, however, never observed a testi- 
cular capsule in this stage, the reason probably being that I have 
not yet examined specimens young enough. At a somewhat later 
stage, the large central cell, spermatogon, begins to subdivide, and 
instead of one large nucleus several large nuclei are seen situated 
in a protoplasmic mass inside the follicular epithelium. I have often 
observed testicular capsules in this stage (vide fig. 12). 
The spermatogon-nuclei continue, however, to divide, and in- 
stead of the original spermatogon, a conglommerate of smaller cells y 
spermatocytes, is gradually formed within the capsules (vide fig. n y 
caj — ca 6 . No protoplasm is left in the centre of the capsule, as 
often is the case. In these spermatocytes plenty of nuclei with 
karyokinetic forms are generally seen (cf. fig. 11). When the 
spermatocytes have become reduced by subdivison to a certain size y 
the testicular capsule is rapidly enlarged, and the spermatocytes 
are gradually separated from each other and isolated (vide fig. u ? 
ca 7 ). They continue, however, to subdivide; fig. 14, a — h and fig. 
15, a — e represent several such spermatocytes with karyokinetic 
forms. When these spermatocytes have, by subdivisions, become re- 
duced to a certain size, they cease to subdivide, i. e. they have 
reached the stage of spermatides; fig. 11, ca 8 represents a capsule 
containing such spermatides. 
By an elongation of the nucleus, as well as the whole body of 
the cell (cf. figs. 16 & 17) these spermatides are now gradually trans- 
formed into ripe spermatozoa. At the same time the capsule is 
prominently enlarged, and its envelope becomes very thin. Fig. 11, 
ca 9 represents part of such a capsule containing spermatides and 
spermatozoa, more or less developed. Fig. 7, caj, ca 2, ca 3 also 
represents similar capsules containing spermatozoa. 
