Observations and Experimonts on the Ctenopborc Ei^<^. 17 



10. Tlie cytuplasin iibove the level of the cleavage bead 

 lias little iniluenee upon the accomplishment of the division. 



17. The accumulation of ectoplasm over the micro-^ and 

 macromere poles is formed in enucleated fragments in the same 

 way as in the whole egg. 



18. If the removal of the nucleated portions is done at the 

 beginning of the division, the cleavage furrow goes on normally 

 irrespective of the angle of the section. If, however, the same 

 operation is ^jerformed upon an egg in which the cleavage has 

 further advanced, the division plane is in most cases turned towards 

 the side of larger amount of cytoplasm, the enucleated fragment 

 being divided into nearly equal parts." 



19. Sometimes in the egg operated on the cleavage furrow 

 curls up towards the macromere pole. 



20. If the "cleavage head" be split lengthwise', a new 

 head " forms nearly at right angles and towards the portion with 

 larger amount of cytoplasm. 



1^1. If an incision is made in the egg in the micromero 

 region the cleavage is not affected. 



VII. General Discussion. 



Three views have been put forth regarding the mechanism 

 of the cytodieresis of the ctenophore egg. Zieglee maintains that 

 the cleavage is accomplished by the constriction of a meridional 

 ectoplasmic thickening, Mvhicli is in turn caused by the " action at 

 a distance '" of the centres and no rays are necessary for cleavage 

 ('03 p. 162).' 



1 strictly speaking-, at the en I of the cleavage furrow, since the a-îcumuLition takes pLicj 

 at the side of the e<;g in case a new cleavage furrow is formed at right angles t j the old, c.jj., 

 PI. IV, Fig. 50. 



2 This result Mas obtained when a large portion was out off from the og^. Xo experi- 

 ment was carried out, to my regret, to test whether or no the removal of a small amount of 

 cytoplasm from an egg with an already far advanced cleavage furrow affects the remaining 

 course of the cleavage plane. 



3 It is interesting to recall liow Kowalkvskt was impresso I when he observed cleaving 

 ctenoi^hore eggs: "wie sonderbar es auch klingen mag, so sc'ieint mich doch diese, S3 zug 

 sagen, todte unbewegliche centrale Masse ganz der mechinischen Pressung von Aussen ; u 

 und keine innfn active Kraft zu besitzen'' ('67 p. 3). 



