AND OF HYBRID PIGEONS. 
9 
apparently in the same condition as before, primary and sec¬ 
ondary spermatocytes may be present. Where one finds the 
primary spermatocytes, they are usually arranged in clumps, 
the individuals of which are at similar points of development. 
The same is true for the secondary spermatocytes. Fig. 2 
shows both kinds of spermatocytes undergoing division in the 
same field of view. 
In the following account, the spermatogonia are considered 
first and the various other types are then taken up in the order 
of their succession in development into spermatozoa. 
A. SPERMATOGENESIS OF NORMAL PIGEONS. 
THE SPERMATOGONIA. 
The spermatogonia lie in a more or less regular layer next 
to the tubule wall. Not infrequently the individual cells have 
the appearance of having been crowded out of place so that the 
layer appears irregular or double. There is considerable vari¬ 
ation in the appearance and some variation in the size of the 
cells at different times. In early stages they are. far apart and 
have small nuclei which are oblong with the long axis parallel 
to the tubule wall. The cells themselves are generally flattened 
more or less so that their long axes coincide with those of the 
nuclei (Fig. 1, sg.). In still earlier stages, the cell boundaries 
are very indistinct or seemingly absent, and gaps frequently 
intervene between the individual spermatogonia, so that they 
appear to have been left behind from a preceding set, or to 
have recently settled in their present position. Some of them 
resemble very much the wandering cells seen outside the tubule 
in the interstitial tissues. 
In later stages, the spermatogonia are crowded together 
until they become more or less columnar in shape (Fig. 2). 
The nuclei increase in size and become very distinct. They are 
round or slightly oval in shape. When oval, the long axis is, 
as a rule, perpendicular to the tubule wall. In the closely 
packed cells, the nuclei come to lie eccentrically as they enlarge, 
and a condensation of the cytoplasm, or mass of sphere sub¬ 
stance (idiozome of Meves), makes its appearance and gradu- 
