294 KING. [Vol. XVII. 



dealing with the various problems of spermatogenesis and 

 oogenesis. The invertebrates have furnished such favorable 

 material for investigation along these lines that as yet but 

 comparatively little work has been done on the higher forms. 



Schultze ('87) was the first to give an accurate account of the 

 ripening of the amphibian ^gg, and his results have been most 

 ably supplemented by those of Born ('92), Fick ('93), and Jor- 

 dan ('93). None of these investigators have, however, given 

 the details of the breaking down of the germinal vesicle, of the 

 formation of the first polar spindle and the subsequent polar 

 divisions, nor of the origin and division of the segmentation 

 spindle. It was with the hope of throwing some light on these 

 questions that the present work was undertaken at Bryn Mawr 

 College in the spring of 1896. To Prof. T, H. Morgan I wish 

 to express my thanks for many valuable suggestions and for a 

 careful supervision and criticism of my work. 



II. Material and Method. 



In the vicinity of Bryn Mawr the common toad, Bufo len- 

 tiginosus, usually comes from its winter hibernation during the 

 first warm days of April, and there is then a period of about 

 three weeks in which the long strings of freshly laid eggs can 

 be easily procured. 



As eggs laid in the laboratory had been found to develop 

 into perfectly normal tadpoles, copulating animals were placed 

 in large glass aquaria containing a small amount of water, and 

 left undisturbed until the eggs were deposited and fertilized. 

 Then, by preserving a number of eggs every five minutes dur- 

 ing a period of an hour and a half, a complete series of the 

 fertilization stages was obtained. 



Material for the study of the maturation processes was 

 acquired in the following manner : females were captured as 

 soon as possible after they had emerged from their hibernation 

 and killed immediately. If the eggs were still in the ovaries, 

 they were transferred to jars of fresh water and a few of them 

 fixed at frequent intervals for several hours, as in three cases 

 maturation was found to continue under these conditions. 



