336 



N. YATSU : OBSERVATIONS AND EXPERIMENTS 



METSCHNIKOFF figures this case (Taf. 24 Fig. 2) though lie docs not 

 mention anything in the text ('85). In such eggs nij is given off 

 horizontally and e, towards the macrotnere pole. There are all 

 gradations between this mode of cleavage and that of ordinary 

 ctenophore type. Fig. I 7 and 8 represent two intermediate stages. 



As is seen from Table III the cleavage of Callianira differs from 

 that of Beroc in the following points, nij is formed earlier and e 4 is 

 given off from the end-cells in Callianira. irij , and m, 2 remain un- 

 divided much longer than those of Beroê. A long pause is found in 

 the 72-ccll stage of Callianira. 



III. Experiments on Cleavage. 



Experiments on cleavage have previously been made by 

 ZlEGLER ('98) and incidentally by FisCHEL ('03). In order to supple- 

 ment their results removal experiments were performed on the eggs 

 of Beroc ovata (eighty-four cases) in various ways and at various 

 periods. As to the method of operation the reader is referred to Fart 

 I 1 of this study. Most of the egg fragments were examined at the 

 1 6-cell stage so as to compare the sizes of the middle-cells, end-cells 

 and their micromcres. 



In the following series isolation experiments are entirely omitted, 

 because they are not so interesting as those to be described in this 

 section : isolated blastomeres cleave as though they were in the 

 whole egg, as I have incidentally attested while experimenting on 

 the problem of germinal localization (cf. DRIESCH u. MORGAN '95). 



a. Experiment 1 [2 cases). 



The egg was cut soon after it was discharged, i.e., before fertili- 

 zation. In two cases the mode of cleavage was studied. Both of 

 thera were found to be normal in spite of the operation. Section 



1) Journal of Science College XXX II. Art. j. 



