AND OF HYBRID PIGEONS. 
41 
The deformed types, in which development is nearly com¬ 
plete, pass through practically the same stages as do the normal 
spermatozoa in their transformation from the spermatids. They 
may come to posses both head-spine and tail (Fig. 40), though 
very frequently the tail is incomplete. In rare instances more 
than one tail appears in process of formation in the same cell, 
although no completely developed forms with two tails were 
observed. 
DEGENERATION OF THE GERMINAL CELLS. 
Degenerative processes were in progress in the testes of all 
the sterile forms, but were most pronounced in hybrids between 
very divergent species, or between unlike hybrids from birds 
which were themselves descendants of fertile hybrids. There 
were some such extreme cases of degeneration that only the 
layer of cells lying along the wall remained in the tubule. 
Where such a degree of degeneration exists there is, of course, 
no approach to the formation of spermatozoa. There is often 
a strong invasion of wandering cells into the tubules, especially 
where the degenerative activity has become extensive. The 
interspaces between such tubules are also usually packed with 
cells which have much the same appearance as white blood 
corpuscles. Little clumps and globules of deeply staining cyto¬ 
plasm are scattered about among the cells within the tubules. 
The oval nuclei of the Sertoli cells are also generally to be seen 
in varying numbers. 
In some places it really looks as if the germinal cells them¬ 
selves lose their cell walls and characteristic appearance and 
become leucocytes, but this point will require very careful study 
before any definite conclusions can be reached. In other 
tubules the original cells, or cells which have wandered in, settle 
down and take on exactly the appearance of the large stroma 
cells which are ordinarily present outside the tubules. The 
cytoplasm of such cells has a peculiar alveolar like appearance 
that is very characteristic. 
In birds where the degenerative processes are not so exces¬ 
sive, the tubules may yet contain large numbers of the germinal 
cells, many of which arc in various stages of decline. The 
primary spermatocytes seem to be the most susceptible to 
