566 Chas. W. Hargitt 



of CiAMiciAN. Coneerniiig- his aecounts of maturation my own ob- 

 servations are luaiiily contirmatory. As to fertilization, however, I 

 have not been able to obtain cytological details (juite comparable 

 with those described by him. Concernine,- nuclear plienomena as- 

 soeiated with thesc processes my observatious confirm in considerable 

 degree those which I have elsewhere described in connection with 

 the development of Pennaria and Eudendrium. There is the same 

 mig-ration of the nucleus to the periphery of the egg, the disso- 

 lution of the nuclear membrane, and the same appareut dissipation 

 of the nuclear substance throughout the cytoplasm of the q^^, fol- 

 lowed later by its apparent reorganization just prior to the first 

 signs of cleavage. 



Cleavage. 



It is perhaps concerning this phase of the life history that most 

 dissension has arisen. Ciamiciax was the first to critically study 

 its development, and in doing so directed his observatious largely 

 to the aspects presented by the living eggs. This he did by cut- 

 ting off Clusters of gonophores and studying them under the micro- 

 scope. Bat as he confesses, the various contractioDS of the several 

 parts of the gonophores and the resulting movements and read- 

 justments so shift the position of the eggs that it is extremely diffi- 

 cult to obtain accurate observations. 



He concluded that cleavage was unequal, the first and third 

 furrows being at right angles to each other and meridional, the 

 second equatorial and from within outward. In later cleavages 

 there is a more rapid di vision of the cells at the animai pole, these 

 later growing over the blastomeres of the vegetative pole by a pro- 

 cess of epibole and enclosing the latter Avhich later form the ento- 

 derm. 



This conclusion has been frequently called in question by later 

 observers. Balfour^ claimed that an examination of segmentation 

 by means of sections failed entirely to confirm Ciamician's resulta. 

 Coxn2 has likewise failed to find any evidences of epibolic gastru- 

 lation in another species of Tubtdaria, and from this has undertaken 

 to discredit Ciamician's conclusions. As is well known from later 

 observations diöercnt species at times show very considerable va- 



' Comparative Embryology, 2d Edition, IS'^S, Vol. 1 pag. 154. 

 ■- Z. Anz. .5. .Jahrg. 1882 pag. 483, 



