32 
SPERMATOGENESIS OE NORMAL 
is t^eld and the other twisted. By referring to Fig. 26 it will be 
observed that a sphere has reappeared in the cell. Its function 
is unknown. It may be used in the completion of the head-spine 
and the tail. The final structure, of the tail is due apparently 
to the growth backward of the cytoplasm along the axial fila¬ 
ment. A sufficient differentiation of the several parts could not 
be obtained to follow out the details of its formation. As the 
spermatozoon attains to its complete adult form, the cyto¬ 
plasmic case around the head disappears, the 'head straightens 
out and is ready for attachment to the Sertoli or nurse cell. Usu¬ 
ally a number of spermatozoa mature at one time and move, 
toward one of the Sertoli cells until the head is imbedded in the 
cytoplasm (Fig. 1). The attraction between the Sertoli cell and 
the spermatozoa seems to result in mutual movement, for as the 
latter approach, the cell, and particularly the oval nucleus, often 
moves inward toward the lumen of the tubule to meet them. A 
striated appearance of the remaining cytoplasm results from 
this inward migration on the part of the nucleus. In osmic 
acid preparations some of these striae can be resolved into what 
appear to be rows of minute oil globules, while others seem to 
have more the nature of filaments of connective tissue. In 
later stages, the cytoplasmic mass of the Sertoli cell diminishes. 
It has evidently been consumed by the spermatozoa. 
The adult spermatozoa becom.e free in the lumen of the 
tubule finally and pass out into the vas deferens and thence to 
the exterior. 
SUMMARY. 
The facts which appear to be. of primary importance as set 
forth in the foregoing pages are briefly as follows: 
1. The usual four types of cells exist in the genesis of the 
pigeon spermatozoon, viz:—spermatogonia, primary spermato¬ 
cytes, secondary spermatocytes and spermatids. 
2. Sertoli or nurse cells are present. 
3. There is a curious ejection of part of the chromatin 
material from the nuclei of the spermatogonia just prior to their 
last division. 
