308 BULLETIN OF THE 



be accompanied by the formation of a wake on the peripheral side of 

 such large granules as cannot be displaced. Any granules carried by 

 the current into this wake will remain there, and thus contribute to the 

 formation of a radial row of granules, and a series of such rows would 

 produce an appearance of striation. 



The conclusions drawn for Elasmobranchs are, that in the earlier 

 stages of segmentation, and during the formation of fresh segments, a 

 partial solution of the old nucleus takes place, but all its constituents ' 

 serve for the reconstruction of the fresh nuclei ; that in later periods of 

 development a still smaller part of the nucleus becomes dissolved, and 

 the rest divides, but that the two fresh nuclei are still derived from the : 

 two sources ; and, finally, that after the close of segmentation the fresh 

 nuclei are formed by a simple division of the older ones. 



LuDWiG ('76, p. 484) believes that in the development of spiders' eggs 

 the increase in the cells may be accompanied by nuclear changes such 

 as have been observed by Fol, Biitschli, and others. Evidence of this 

 is to be found especially in the radial direction of the deutoplasmic ele- 

 ments in the separate cell territories and the appearance of the nucleus 

 in the centre of this radial structure, as well as in the fibre-like (strang- 

 artig) connection of two recently separated centres. 



The origin of the nuclei (p. 476) was not satisfactorily made out. In 

 one case the nucleus seemed to arise by a fusion of a number of small 

 round structures, in which case the central mass assumed a foamy ap- 

 pearance which disappeared as soon as the nucleus became visible. One 

 might conclude that the nucleus arose by a fusion of the vacuoles which 

 caused the foamy appearance, were it not for the fact that the vacuoles 

 were sharply — the nucleus only indistinctly — outlined. 



The fusion of the deutoplasmic balls into columnar structures, and the 

 radial arrangement of the latter (p. 474), the author refers not to any 

 subjective activity of the deutoplasm, but considers as a passive phe- 

 nomenon brought about by the active vital processes in the protoplasm. 



In his book on Zellhildung und Zelltheilung, Strasburger {'76) availed 

 himself of the then recently made observations on cell division by Auer- 

 bach, Biitschli, and others, to show the prevalence of the phenomena 

 observed by him to take place in plants. To these evidences he adds 

 (pp. 208-231) observations of his own. Those relating to the changes 

 occurring in the cell division of cartilage are considered in another 

 connection. His other observations were made on the eggs of Phallusia 

 mammillata and Unio pictorum. 



In artificially fecundated eggs of Phallusia the nucleus of the first 



