No. 2.] THE SEA-URCHIN EGG. 47 1 



The undetermined question is whether such areas can arise 

 in a morphological sense de novo, for example, as focal points 

 in a moving equilibrium of forces pervading the cell as a whole, 

 or whether they are always the effect of a material body pre- 

 existing as a formative center and having a persistent identity, 

 as expressed by the power of growth and division, together 

 with the persistence of the daughter-bodies. Speculative 

 cytology has of late no doubt tended towards the latter conclu- 

 sion, and, as far as the nucleus considered as a whole is 

 concerned omnis nucleus e micleo, appears to be a statement 

 of universal application. There are, however, facts which raise 

 doubts as to how far this case can be taken as typical of other 

 parts of the cell, and the most striking of these facts are 

 afforded by the history of the nucleus itself. We see here the 

 chromatic substance giving rise to bodies, the chromosomes, 

 which are periodically differentiated in characteristic form and 

 number out of an unformed basis, which grow, divide by fission, 

 and are finally restored again into the common basis, merging 

 into it their own individuality. In this case only the specific 

 material of the dividing body persists, while its morphological 

 individuality disappears ; and there is absolutely no proof that 

 the chromosomes emerging from the network at the succeeding 

 division are the same " individuals " {i.e., the same group of 

 individual molecules or other ultra-microscopical units) as 

 before, or that the formative center of each chromosome is a 

 material body. The constancy in their number may with equal 

 reason be regarded as the outcome of formative process {i.e., 

 at bottom chemical changes) affecting the chromatin-mass as 

 a whole and causing it to crystallize, as it were, in a particular 

 form at certain focal points. 



May not other cell-organs, not only those that are mere 

 temporary structures, such as pseudopodia or cilia, but also 

 such as are capable of growth and division, arise in a similar 

 manner and be the result rather than the cause of the chemical 

 differentiations that they exhibit > It may be said with justice 

 that this is but a hypothetical restatement of the problem, 

 which explains nothing. But even such a hypothetical sug- 

 gestion may have some value, if only as a protest against the 



