I 2 



N. YATSU : OBSERVATIONS AND EXPERIMENTS 



5. Development of the first quartet cell in 

 isolated fragments. 



FlSCHEL'S conclusion that the entire ctenoplasm is located in the 

 first quartet cells ('97 p. 122), was tested in various ways and that 

 was found to hold in almost all cases, e. g., 2E + e, + M-fm, 1 produced 

 an embryo with two comb-rows and 3M-f3m + e, that with four rows 

 In some cases, however, the first quartet cells deprived of the asabl 

 blastomeres seem to fail to develop comb-plates altogether as is seen 

 from the following experiments : 



2E + 2M-I- 4e, + 4m, should produce eight-rowed embryo but this 

 gave rise to an embryo with six rows of combqolates. 5E+ 2M + 4e, 

 -f 4m! also yielded an embryo with six rows ; 4E + 4e, + 4111, , six rowed 

 embryo. 



6. Summary. 



1. Germinal localization becomes more definite after the formation 

 of the polocytes. 



2. Each of twin embryos produced from an egg by an equatorial 

 section before the first cleavage may possess the apical sense organ. 



3. Since some of the blastomeres of the 8-cell stage or, more pre- 

 cisely speaking, those of the first quartet fail in some cases to devclope 

 comb-rows, the importance of correlative differentiation should not be 

 overlooked in the development of the ctenophore egg. 



4. Very rarely the distribution of the ctenoplasm among the 

 blastomeres of the 8-cell stage may vary so that the number of comb- 

 rows in resulting embryos exceeds that of the initial blastomeres. 



Zoological Institute, Tokyo Imp. Univ. 

 October 28, 191 1. 



I Here Ii and M indicate the basal cells after the first quartet being given off. 



