JOURNAL OF THE COLLEGE OF SCIENCE, LMPEEIAL UNIVERSITY. 

 TOKYO. JAPAN. 



VOL. XXXII., ARTICLE 3. 



Observations and Experiments on the Ctenophore Egg: 



I. The Structure of the Egg and 

 Experiments on Cell- division. 



By 

 Naohide Yalsu. 



Introduction. 



The ctenophore egg has become classic in experimental em- 

 bryology through the invaluable papers of Chun ('92), Driesch 

 and Morgan ('95), Ziegler ('98, '03) and Fischel ('97, '98 and 

 '03). Singularly enough, however, since the appearance of these 

 works no further detailed analytical studies on the interesting egg 

 have been undertaken. At the suggestion of Professor E. B. 

 Wilson, the writer made observations and experiments upon the 

 egg of four common species of ctenophore in the spring of 190G, 

 at the Naples Zoological Station.^ 



The present paper deals first with the structure of the egg 

 with a note on the polocy tes and on fertilization ; secondly, with 

 observation on the process of cell-division, mainly that of the first 

 cleavage; and thirdly with experiments performed upon the egg 

 of Beroë ovata. It Avill be followed by two other papers; one on 

 cytogeny and experiments on cleavage physiology, and the other 

 on germinal localization. 



As to experimentation, I wish to lay especial stress upon the 

 following points. Great care was taken to secure good water quite 



1 This study was made with the aid of a grant from the Carnegie Institution at 

 Washington, for which I take this opportunity to express my gi-atitude. I also have pleasure 

 L n acknowledging my indebtedness to the staff of the Naples Zoological Station. 



