SPERMATOGENESIS OF THE PIG WITH SPECIAL 



REFERENCE TO THE ACCESSORY 



CHROMOSOMES. 



J. E. WODSEDALEK, PH.D. 

 ZOOLOGICAL LABORATORY, UNIVERSITY OF WISCONSIN. 



CONTENTS. 



I. Introduction 8 



II. Material and Methods 9 



III. General Arrangement of the Germinal Cells 10 



IV. Spermatogonia 1 1 



V. Primary Spermatocytes 13 



1 . Resting Stage 13 



2. Synizesis and Growth Period 13 



3. Reduction Division 14 



VI. Secondary Spermatocytes 15 



1 . Dimorphism 15 



2. Second Reduction Division (Equational) 16 



VII. Spermatids 19 



VIII. Development of the Spermatozoa 19 



IX. Variation in Size of Mature Spermatozoa 25 



X. Relation of the Accessory Chromosomes to Sex in the Pig 25 



i. Dimorphism in the Number of Chromosomes of the Male and 



Female Germinal and Somatic Cells 28 



XI. Summary 28 



INTRODUCTION. 



In late years the occurrence of accessory chromosomes, in 

 various degrees of complexity, has been recorded from diverse 

 groups of invertebrates. Recently the field has been extended 

 to the vertebrates, Guyer having shown their existence in the 

 males of the guinea ('090), rooster ('09^), rat ('10), and man 

 ('10); Newman and Patterson ('10) in the armadillo; Jordan 

 ('n) in the opossum; Stevens ('n) in the guinea-pig; and King 

 ('12) in Necturus. The existence of what appears to be such an 

 element has also been reported in the ovary of the cat by Wini- 

 warter and Saintmont ('09). In a recent paper Jordan ('13) 

 states that the heterochromosomes are unquestionably lacking 

 in the pig. I find, however, that the accessory chromosomes are 

 very conspicuous in all of the pig material which I have studied. 



8 



