154 EZRA ALLEN 



The spermatids 



The chromosomes aggregate about the pole of the daughter cell 

 of the second spermatocyte division and quickly form a mass. 

 This breaks up again into chromosomes which are very woolly 

 and indistinctly differentiated. They gradually become more 

 diffuse, their staining reaction diminishes, and they are lost to 

 view. These conditions are shown in figure 1, the progressive 

 stages, except the final, appearing in the cells marked Sptd. 1, 

 Sptd. 2, and Sptd. 3. I have not been able to make counts nor 

 to distinguish an accessory, the chromosomes are so closely 

 intermingled and interconnected by the woolly threads. Grad- 

 ual changes transform the spermatid into the mature sperma- 

 tozoon. Sertoli cells are present and play their customary part. 

 In a few anunals studied a small amount of degeneration of 

 these spermatids was seen, but in other animals none. It is 

 doubtful if extensive degeneration is ever the rule in healthy in- 

 dividuals unless at old age, a stage which I have not studied. 

 The cytoplasmic phenomena of special interest are discussed on 

 page 169. 



Conclusions with regard to the chromosomes 



In the standard albino rat of The Wistar Institute colony the 

 diploid number of chromosomes is 38, the haploid 19; there is one 

 accessory which divides in the second spermatocyte division. 

 These chromosomes are of three forms in the first spermatocytes, 

 viz., the ring (simple or compound), the cross, and the rod, the 

 last-named found only in the accessory. The rings and crosses 

 are tetrad in constitution, so organized that the chromatids may 

 retain their individuality throughout the movements previous 

 to division; fiber attachment is terminal; simple V's are produced 

 in anaphase. The rod form of the spermatogonial chromosomes 

 reappears in interkinesis and in the second spermatocytes, with 

 terminal spindle fiber attachment. The spermatids are dimor- 

 phic, arising as they do from dimorphic second spermatocytes 

 of 18 and 19 chromosomes, respectively. 



