260 T. IWAKAWA. 



The Genesis of ihe Egg in Tkiton. (With Plates XXII, 

 XXIII and XXIV.) By Mr. T. Im akawa. 



Contents. — Some general remarks, 260. The manner of depositing 

 the egg, 262. The structure of the ovary, 262. Origin of the ovum, 26i. 

 Epithelial islands, 266. Formation of yolk-spherules, 271. Vitelline 

 membrane, 273. The germinal vesicle, 274. The " yolk -nucleus," 27fi. 

 Bibliography, 277. Explanation of plates. 



In the spring of 1880 I began, at the suggestion of my 

 highly-esteemed teacher, Mr. Whitman, to study the early 

 stages in the development of our common Triton {T. pyr- 

 rhogaster, Boje) (1). 



It was my intention, circumstances favouring, to study 

 the whole series of events, from the original egg-cell to the 

 transformation of the embryo. The spring and summer 

 were mainly devoted to a study of the cleavage and the ex- 

 ternal changes of the embryo. The appearance of the two 

 important memoirs of Bambeke (3) and Clarke (3), covering 

 the same ground, makes it unnecessary to publish my earlier 

 observations. 



The present paper, which treats mainly of the genesis of 

 the Q^^, was begun in the autumn of 1880, and concluded 

 in June, 1881. Owing to the want of proper aquaria I have 

 obtained very few fresh-laid eggs, and have, therefore, failed 

 to make anything more than fragmentary observations on 

 the changes that follow impregnation. 



With reference to method of hardening, I have been most 

 successful with the picro-sulphuric acid of Kleinenburg. 

 For staining fluids I have made use of picro-carmine, hse- 

 matoxylin, and Beal's carmine. Silver nitrate was employed 

 to obtain surface views of the ovary. 



Some General Remarks. 



Triton pyrrhog aster is very common in this island, being 

 found in ponds, brooks, ditches, and rice fields. It occurs 

 very abundantly in the pond of Inokashira, located about 

 ten miles west of Tokio, from which place most of my speci- 



