author's abstract of this paper issued 

 by the bibliographic service april 20 



STUDIES ON CELL DIVISION IN THE ALBINO RAT 



(Mus norwegicus albinus) 



III. spermatogenesis: the origin of the first spermato- 

 cytes AND the organization OF THE CHROMOSOMES, 

 INCLUDING THE ACCESSORY 



Ezra' allen 



Department of Zoology of the University of Pennsylvania and the Laboratory of 



the Wistar Institute 



FIFTY-EIGHT FIGURES (fIVE PLATES) 



I . Introduction 134 



II. Material and technique 134 



III. Observations 136 



The structure of the rat testis 136 



The spermatogonia! chromosomes 137 



The history of the chromosomes during the first spermatocyte changes . 138 



1 . The early period 138 



Preleptotene stages 138 



Leptotene stage 139 



Zygotene stage 140 



Pachytene stage 140 



Conclusions 140 



2. The later period 140 



Diakinesis 141 



The shapes of the first spermatocyte chromosomes 141 



The composition of the first spermatocyte euchromosomes. . 144 

 Conclusions as to the constitution of the first spermatocyte 



euchromosomes 148 



3. The number of the first spermatocyte chromosomes 148 



4. The sizes of the first spermatocyte chromosomes 150 



5. The arrangement on the spindle 150 



6. The nucleolus • 151 



7. The history of the accessory 151 



Interkinesis and second spermatocytes 153 



The spermatids 154 



Conclusions with regard to the chromosomes 154 



Cytoplasmic structures 155 



133 



