UNIVERSITY OF CALIFORNIA PUBLICATIONS 



IN 



ZOOLOGY 



Vol. 16, No. 19, pp. 371-380, plate 30 January 22, 1917 



SOME PHASES OF SPERMATOGENESIS /^s<""*" '''«/7^ 

 IN THE MOUSE 



HARRY B. YOCOM 



CONTENTS 



PAGE 



Introduction 371 



Methods 372 



Structure of the testes 373 



The primary spermatocyte 374 



Secondary spermatocyte 375 



Spindle fibers and centrosome 377 



Summary 378 



Literature cited 379 



Explanation of plate 380 



INTRODUCTION 



The problems of the number, behavior, and peculiarities of the 

 chromosomes during the process of spermatogenesis have been of 

 absorbing interest for manj^ years. Until recently they have bepn 

 studied largely in insects, perhaps because many species of these 

 animals have relatively few chromosomes, a fact which enables the 

 investigator to work with greater precision and certainty. The 

 chromosomes of mammals have been less studied, and only within re- 

 cent years has there been much intensive work done on them. Many 

 of the less difScult problems have even been overlooked. The number 

 of chromosomes in many of our more common mammals has not been 

 definitely established ; and as to their behavior during the process of 

 maturation of the germ cells, little has been proved beyond question. 



The common house mouse has been the subject of considerable 

 cytological investigation. Tafani (1889) claimed that it had twenty 

 chromosomes. Sobotta (1895) fixed the number at twelve, but later 



