Helen Dean King 349 
two acroblasts thus formed separate, and after mitosis is completed one of 
them is to be found in each of the daughter-cells. An equatorial section of 
the spindle of a primary spermatogonium during metakinesis occasionally 
shows the two acroblasts lying together in the cytoplasm near the 
chromosomes (Fig. 4, 4); usually, however, the acroblasts separate be- 
fore this time and are not to be seen in such a section of the cell. Not 
infrequently the acroblast can be found on the spindle among the chromo- 
somes (Fig. 9, A). In such cases, if the preparation has been stained 
with iron-hematoxylin, the acroblast appears as a very small, round 
chromosome, and it might readily be mistaken for an “ accessory ” 
chromosome if its previous history had not been ascertained. The 
acroblast divides in each of the spermatogonial mitoses and also in both 
of the maturation divisions, so that one of these bodies is to be found in 
the cytoplasm of every spermatid. In the spermatid the acroblast under- 
goes a final division and one part migrates to the anterior end of the 
spermatid to form the acrosome; the other part remains in the posterior 
region of the spermatid and eventually disappears. 
According to the researches of La Valette St. George (53), Meves (35), 
Benda (2), and McGregor (34), the primary spermatogonia in the 
amphibian testes divide amitotically and the descendants of these cells 
become functional spermatozoa. In Salamandra, according to Meves 
and Benda, this division takes place by means of the constrictive power 
of a ring-shaped centrosome; in Amphiuma, McGregor finds that the 
nucleus is divided by a simple cleft into two nearly equal parts. Al- 
though I have carefully searched through many sections of testes con- 
taining large numbers of primary spermatogonia, I have never been able 
to discover a single cell which I could be sure was dividing amitotically. 
In the large spermatogonia the nucleus is often found to be much more 
irregular in outline than that shown in Fig. 1, and not infrequently it 
appears to be composed of two or more large lobes which are connected 
only by a very narrow bridge of nuclear substance. In these cases, how- 
ever, the outline of the cell is invariably rounded, and I have never 
found any indication of a division of the cytoplasm. If amitotic division 
of the primary spermatogonia occurs in the testes of Bufo, it is exceed- 
ingly rare and probably, as suggested by vom Rath (46), the cells divid- 
ing in this manner are in the process of degeneration and never develop 
into mature spermatozoa. 
In every case in which I have observed the division of the primary 
spermatogonia the process has been taking place karyokinetically. In 
the early prophase of mitosis all of the nucleoli disappear and the 
