30 SCIENCE PROGRESS. 



it. But we cannot as yet answer the more obvious and, one 

 might think, almost preliminary question as to what the 

 chief functions which are discharged by these two com- 

 ponents really may be. It is certain that the existence of a 

 nucleus is essential to morphological development such as is 

 implied in the production of new cells, and very probably 

 also in the further differentiation of those which have 

 already been formed. Instances of this are seen for example 

 in the growth or alteration of the cell wall. Haberlandt 

 (5) some years ago drew special attention to the fact 

 that when local thickening occurred in a cell wall the 

 nucleus commonly moved to this spot, and the present 

 writer has repeatedly observed it during the formation of 

 the hard coat found on many seeds ; here the deposition of 

 substance is usually localised on the inner parts of the cell, 

 and the nucleus takes up a corresponding position as soon 

 as the process begins. Korschelt (6) has observed a 

 similar relation to exist during the chitinisation of the mem- 

 branes of insect cells, and quite recently Istvanffi (Ber. Deut. 

 Gesel., Dec, 1895) has observed that when the tubular 

 hypha of Mucor branches, a nucleus is invariably present at 

 the spot whence the branch is arising. Strasqurger (3^) has 

 also drawn attention to the same truth, inasmuch as he 

 states that before the opening of the zoosporangium of 

 CEdogonium, the nucleus and kinoplasm aggregate in the 

 vicinity of the spot at which the hole is about to be formed. 



But perhaps one of the most striking instances of the 

 directive effect of the nucleus as a whole is to be seen in 

 the result of an experiment of Boveri, who asserts that he 

 impregnated a non-nucleated piece of protoplasm of an 

 echinoderm ovum with the sperm nucleus of another species ; 1 

 development ensued, and the larva resembled the paternal 

 form (7). 



In discussing the relations which exist, or are supposed 

 to exist, between the cytoplasm and the nucleus, it is clearly 

 of the first importance to know what are the changes which 

 occur in them, and especially in the nucleus, during the 



1 The animals actually employed were Echinus microtuberculatus 

 (male), and Sphaerechinus granulans (female). 



