134 EZRA ALLEN 



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IV. Discussion ' 155 



The number of the chromosomes and the accessory 155 



The constitution of the first spermatocyte chromosomes 159 



The spermatogonia and Sertoli cells 160 



The age when the first spermatozoa are ripe 166 



Cytoplasmic structures 169 



V. Conclusions 172 



VI. Literature cited 173 



VII. Explanation of figures. Plates 175 



1. INTRODUCTION 



Purpose and scope of the study. On account of difficulties 

 experienced in fixing mammalian material, great disagreement 

 exists in the literature on mammalian spermatogenesis, not only 

 concerning the number of chromosomes, but also concerning 

 such important points as the presence and nature of an accessory, 

 and the forms, constitution, and history of the individual chromo- 

 somes. My study on the germ cells of the white rat was begun 

 with the hope of solving some of these problems for one mammal. 

 The results recorded in this paper set forth the basal number of 

 chromosomes, the presence of one accessory, and the shape, 

 organization, and behavior of most of the chromosomes through-' 

 out their history in spermatogenesis ; the development of the first 

 spermatocyte cells from spermatogonia; also a statement of the 

 problems with respect to the origin of spermatogonia and Sertoli 

 cells, and the cytoplasmic bodies known as the idiosome and the 

 chromatoid body. Spermiogenesis is not discussed. 



2. MATERIAL AND TECHNIQUE 



Material. The rats came from the colony of The Wistar 

 Institute of Anatomy and Biology. Only the standard strain of 

 Albino was employed. Over one hundred individuals contrib- 

 uted to the study, aged from birth to full maturity. Most of 

 them were used in obtaining a satisfactory method of fixation 

 and preparation. 



The traditional fixatives and technique had proved inadequate 

 in the hands of previous workers and were equally so in mine. 

 After experimenting with practically every well-known fixative 



