252 
J. 0. Wakelin Barratt and G. Arnold 
Sciiöxfeld 1 ), Moore and Walker 2 ), and Duesberg 3 ). In writing this ac- 
count we have f ollowed the last writer to whose Figures the reader is referred, 
only such illustrations of the normal changes, resulting in the formation 
of spermatozoa, being introduced in this paper as are necessary to a clear 
understanding of the degenerative processes induced by X rays. 
When a seminiferous tubule is viewed in section it is seen to be 
bounded externally by a basement membrane (Fig. 32). The cells lying 
immediately in contact with the basement membrane are of tlrree kinds; 
foot cells or cells of Sertoli; spermatogonia; and spermatocytes of the 
first order. Next appear still more spermatocytes of the first Order, and 
forming the innermost layer of the tubule are smaller cells consisting of 
spermatocytes of the second order, spermatids, and spermatozoa. These 
various types of cells are not, however, confined to any particular layer, 
but are more or less intermingled. 
The course of development of the sexual cells in the seminiferous 
tubules is as follows. The germinal cells lying in contact with the base- 
ment membrane, the spermatogonia. give rise by division to further 
spermatogonial cells and to spermatocytes of the first order. The latter 
undergo a reduction division. the daughter cells being termed spermato- 
cytes of the second order. These again divide in their turn producing 
daughter cells known as spermatids, which pass through a series of changes, 
becoming thereby converted into spermatozoa. The cliaracters of these 
various types of cells and the changes whicli they undergo will now be 
further outlined. 
The spermatogonia are small cells, which generaüy, in virtue of 
their position on the basement membrane, present the flattened appearance 
sliown in Fig. 2. Relatively to the nucleus their cytoplasm is not abundant. 
The nucleus usually contains three or four dark masses of chromatin con- 
nected by finer Strands of linin, which are more distinct in some of the 
spermatogonia tlian in others. Division in the spermatogonia conforms 
to the somatic type, illnstrated in Fig. 3, and the ultimate products of 
the division are two cells whose appearance is at first precisely similar 
to the spermatogonium from which they are derived. One of the latter 
1) Schönfeld, H. La spermatogenese chez le taureau: travail complet. Arcli. 
de Biologie. 1901. T. XVIII. 
2 ) Moore, J. E. S. and Walker, C. E. The meiotic Process in Mammalia. 
Liverpool University Reports. 1906. 
3 ) Duesberg, J. 1. Les divisions des spermatocytes chez le rat. Archiv f. Zell- 
forschung. 1908. Bd. I. S. 399. 2. La Spermiogenese chez le rat. Ibid. 1909. Bd. II. 
S. 137. 
