THE OVUM OF THE NINE-BANDED ARMADILLO. 

 GROWTH OF THE OVOCYTES, MATURATION AND 



FERTILIZATION. 



H. H. NEWMAN. 



TABLE OF CONTENTS. 



I. Introduction 100 



1 1 . Literature on mammalian ovogenesis 103 



III. Material and method 104 



IV. Scope and outline of observations 106 



V. Development of the Graafian follicles 107 



VI. Development of the ovocytes with especial reference to vitellogenesis 



and to the comparative rate of growth of nucleus and cytoplasm. . 112 



VII. Nuclear changes during the growth period of the ovocytes 117 



VIII. The first polar spindle 120 



IX. The first polar body and the second polar spindle 122 



X. The second polar body and the female pronucleus 124 



XI. An anomalous case of a third polar spindle 124 



XII. Fertilization 125 



Summary and conclusions 126 



Literature list 128 



I. INTRODUCTION. 



Interest in the armadillo ovum is due chiefly to its unique 

 capacity for polyembryonic development. As has been shown 

 (Newman and Patterson, '10) the ovum develops throughout 

 the early stages of the embryonic period as a single blastodermic 

 vesicle and, only after the differentiation of the primary germ 

 layers, divides visibly into four embryonic primordia. That the 

 four embryos of a litter are always of the same sex has also 

 aroused the interest of biologists, especially those engaged in 

 researches on the problem of sex determination. Since in the 

 armadillo sex would seem to be predetermined in the undivided 

 oosperm an examination of the cytology of both male and female 

 sex cells should be made. 



Many conjectures as to the underlying cause of polyembryony 

 in the armadillo have no doubt been made by all who have taken 

 an interest in the phenomenon. Among those that have been 

 most commonly suggested are the following: 



100 



