577 



From time to time in the second division of the spermatocytes 

 six chromosomes were observed but they were by no means of fre- 

 quent occurrence. They may have resulted either through the per- 

 sistence of the round component of the odd chromosome as a separate 

 individual or through a failure to pair on the part of two of the or- 

 dinary chromosomes. Very exceptionally seven chromosomes were ob- 

 served at the time of the second division. Figs. 17 to 21 represent 

 late prophase or early metaphase in the second division of sper- 

 matocytes which show five chromosomes. Figs. 25, 26 and 27 show 

 corresponding stages in secondary spermatocytes with but four chromo- 

 somes. Fig. 28 represents an anaphase of the latter type. Fig, 23 

 is from a smear preparation of a mass of cytoplasm which contained 

 two spindles, one bearing four, the other five chromosomes ready for 

 the second division. In Fig. 22 is seen a secondary spermatocyte 

 ready for division in which the odd chromosome stands well apart 

 from the other at the equator of the spindle. 



At the second division of the spermatocytes the odd chromosome 

 rarely manifests its compound coadition. As in the guinea it may 

 lag considerably behind the other chromosomes. Fig. 24 shows it in 

 process of division. 



In the transformation of the spermatid into the mature sper- 

 matozoon, while there may be some variations in the details, the or- 

 dinary progression of stages is that represented in Figs. 29 to 32. 

 The four (or five) chromosomes from the last division arrange them- 

 selves in more or less of a closed ring around which the nuclear 

 membrane forms (Fig. 29). Soon the chromatin begins to concentrate 

 gradually toward one side of the nucleus along the periphery until 

 it forms a conspicuous crescent (Fig. 30) which broadens and shortens 

 (Fig. 31) as the process continues. The nuclear membrane thins out 

 along the margin free from chromatin and finally fades away leaving 

 a dense elongated chromatin mass rounded at one end and sharp 

 pointed at the other, to lengthen out into the head of the adult sper- 

 matozoon. At the disappearance of the original nuclear membrane 

 the developing head is seen to be provided with a well-marked head 

 spine at the pointed end and to be united with the axial fiber of the 

 tail at the rounded end. This fiber, at its point of departure from 

 the main mass of cytoplasm, bears a centrosome which as in the 

 pigeon and the guinea surrounds it in the form of a ring. Fig. 33 

 shows the head and a short section of the tail of a mature sper- 

 matozoon. At the anterior end the head spine may be observed. 



As in the guinea there are seemingly two distinct sizes of sper- 



Anat. Auz. XXXIV. Aufsätze. 37 



