MUSEUM OF COMPARATIVE ZOOLOGY. 381 



nucleus has become superfluous, and has consequently disappeared en- 

 tirely from the development. 



The substantial identity of cell division with plants and animals 

 allows Strasburger to conclude that cell formation is induced by the 

 same forces throughout the whole realm of organized beings. Whether 

 this identity justifies the conclusion that animal cells and plant cells are 

 homologous, — that consequently animals and plants have a common 

 origin, — is much less certain. It is not possible, a priori, to positively 

 deny that the successive events of cell division are an immediate me- 

 chanical necessity. The latter cannot, for the present at least, be de- 

 monstrated ; but its possibility once granted, it is clear this agreement 

 in the succession of events no longer serves as evidence of a direct 

 (genetic) relationship between the objects under consideration. 



Other processes of cell formation — freie Zellbildung, Vielzellbildung, 

 Vollzellbildung (or, better, Einzellbildung) — are to be considered as 

 abbreviations of cell division. Successive stages in this process of 

 abbreviation are demonstrable. For example, in the egg of the Abie- 

 tinese the four cells which are formed after the dissolution of the old 

 nucleus about four newly made free nuclei are arranged just as though 

 they had been formed by the repeated division of an apical cell. This 

 presents a case less removed from normal division than is that where 

 (Ephedra) the resulting cells no longer retain any definite topographical 

 relationship. The spores of the Ascomycetse are produced by free cell- 

 formation, namely, a dissolution of the nucleus of the mother cell and 

 the simultaneous appearance of as many secondary nuclei as there are to 

 be spores ; but in some cases it has been shown that the necessary 

 number of nuclei arise by successive dichotomous division. The ex- 

 tremest modifications are such as occur when the old nucleus is not 

 dissolved before the beginning of the free cell-formation, but is pushed 

 to one side and remains unemployed, while new cells arise out of a part 

 of the protoplasm of the mother cell, as is exemplified in the formation of 

 the " Keimblaschen " and their " Gegenfiisslerinnen " with metasperms. 

 , A somewhat similar case (Isoetes) I have considered above, and am 

 'not entirely satisfied that this last one may not also be found on closer 

 ! study to diverge less from the normal method of cell division than we 

 ■are warranted in concluding from Hofmeister's investigations. 



Animals afford less opportunity for the study of " free cell-formation " 



ban plants, and it may appear hazardous to venture any suggestions as 



[to a possible point of comparison. There is, however, in the embryology 



3f some animals a method of cell production which appears to be closely 



