ON THE CTENOPHORE EGG. 



337 



plane was not determined, and the cases were tou few to draw any 

 conclusion from. Further experiments; with exact determination of the 

 section plane by means of the polocytes are very desirable. 



b. Experiment II do cases). 



The egg with the first and second polocytes was cut along 

 various planes before the beginning of the first cleavage. ZlEGLER 

 l'yS) mentions two such cases, figuring' the 2-ccll stages alone. 



Three eggs were cut vertically (Fig. II. 9, io 1 ). One notices at once 

 abnormal proportion of the end-cells and the middle- cells {cf. Fig. I 

 1-3). Nevertheless it is a whole cleavage, the micromere; being 

 formed normally. 



Six eggs were cut obliquely. The result was the same as that 

 of vertical sectioning. In one case, however, the end-cells divided in 

 two equally, instead of sending out a microinere (ej) as is shown in 

 Fig. II 11. 



One egg was cut horizontally'. The end-cells were very small, 

 but the micromcres (e,) are almost as large as in the normal egg. 



This scries of experiments clearly show that at whatever angle 

 the section may strike (if the operation be done before the beginning 

 of the first division) the fragments perform a whole cleavage. More- 

 over it should be noticed that the end-cells are more affected in size 

 by the cutting than the middle- cells. 



c. Experiment III (seven cases). 

 At the beginning of the first cleavage the egg was split into two 

 nucleated fragments. No matter how section plane may pass, the 

 result was in all cases half-cleavage (Fig. II. 13 and 14). 



1) All the figures are drawn ini the sama .magnification.^ x 40)- The micromere pole is 

 directed upward in the figures. The end-cells and their micromeres are represented in 

 heavier lines. 



2) r.jth the halves of this egg develops 1 into larvae, owing probably to the fact either 

 that it was a dispermìe egg or that the germ -nuclei in it did not unite.. 



