MUSEUM OF COMPARATIVE ZOOLOGY. 307 



bodies are not only found in the cells of the germinal disk, but also in 

 the yolk completely outside the disk. From this the author concludes 

 that these bodies can occur where their connection with cell division is 

 altogether out of the question, — where, in their changes, they are with- 

 out any influence on the surrounding protoplasm. 



In later stages of segmentation the conelike bodies are less frequently 

 met with, notwithstanding the fact that the nuclei are more numerous, 

 and are increasing in number more rapidly than during earlier stages. 

 Other bodies are seen, however, which are intermediate between them 

 and ordinary nuclei. Of the three figures (8 a—c) given of these inter- 

 mediate structures, one (8 a) is evidently a spindle in which the nuclear 

 plate is about dividing, and another (8 c) is a more advanced stage, while 

 the third is not so easily referable to known stages in the metamorphosis. 

 Balfour affirms that the granules contained in these bodies exactly re- 

 semble the granules of typical nuclei. All these bodies occupy the place 

 of, and stain like, ordinary nuclei, and are as sharply defined. The 

 true nuclei of the germinal disk are for the most part regularly rounded ; 

 those of the yolk are often irregular in shape, and provided with knoblike 

 projections, indicative of a process of division in the primitive nucleus.* 

 In no case is a distinct membrane to be seen around any of the nuclei. 



Balfour's conclusions, drawn from a comparison of his results with 

 those of other observers, may be reproduced in his own words : — 



" In the act of cell division the nuclei of thfe resulting cells are formed 

 from the nucleus of the primitive cell. This may occur, — 



"(1.) By the complete solution of the old nucleus within the proto- 

 plasm of the mother cell, and the subsequent reaggregation of its matter 

 to form the nuclei of the freshly formed daughter cells ; 



" (2.) By the simple division of the nucleus ; 



" (3.) Or by a process intermediate between these two where part of 

 the old nucleus passes into the general protoplasm and part remains 

 always distinguishable and divides ; the fresh nucleus being in this case 

 formed from the divided parts as well as from the dissolved parts of the 

 old nucleus." 



A series of all possible gradations between the first and second, may 

 be embraced under the third. 



Balfour's conception of the cause of the stellate figures is more me- 

 chanical than that of Auerbach, whom he in the main follows. The 

 streaming out of the protoplasm of the nucleus into that of the cell will 



* It is more likely that these projections are stages in the confluence of several 

 vesicles to constitute a nucleus. 



