Observations and Experiments on the 

 Ctenophore Egg: 



II. Notes on Early Cleavage Stages and 

 Experiments on Cleavage. 



BY 



Naohifle ïatsu. 



The early history of the egg cleavage of Beroc ovata has 

 been studied up to the 120-cell stage by ZlEGLER ('98). And this is 

 the only work, in which the ctenophore cytogeny has been studied 

 up to so far advanced a stage. In connection with my experimental 

 work on cleavage, early developmental stages of three common species 

 of ctenophorcs at Naples, Beroc ovata, B. forskalii and Callianira 

 Inalata, were studied. 



1. Early Cleavage of Beroe. 



As is seen from Table I, appended to the end of this paper, the 

 cleavage of the egg of Beroc ovata was followed up to the 136-celI stage. 



The type of cleavage, as is well known, is biradial or disym- 

 mctrical conforming to the architectonic of the adult. I would call, 

 for the sake of brevity, the submedian or subventral cell middle-cell 

 (M) and the subtentacular cell end-cell (E). The former is larger 

 than the latter and is situated a little towards the macromere pole. 1 

 The subsequent history of these two kinds of cells is different ; each 

 of the middle-cells gives off two micromeres (iTij and m 2 ), while tin; 

 end-cells three (c,, c, and e 3 ). After the micromeres are budded off 

 each macromere is divided in two equal daughter cells, thus producing 

 sixteen entoderm cells. 



I) Macromere pole = vegetative pole of Hatschek (Korscheit und Heider '09 p. 2-p, the 

 pole from which the polocyte> arc expelled. 



