SECT. lo] THE NITROGENOUS EXTRACTIVES 



51 



Aplysia 



who evolved before long more or less quantitative methods of 

 measuring it. As the basic nature of the work was always micro- 

 scopical, these methods were restricted to the measurement of areas 

 and surfaces. The school of Godlevski, which was pre-eminent in 

 this field, used the method of drawing the cell and nucleus with 

 a camera lucida, and then cutting out the drawing, pasting it on 

 cardboard, and weighing the cardboard. Details of this method may 

 be found in Godlevski's paper 

 of 1 92 1. It could not commend ^^ 

 itself to anyone with a physico- ■- 

 chemical turn of mind, for it J 

 depended on the assumption i 

 that the surface area as seen f 

 microscopically bore a uniform I 

 relation to the mass, which, in s 

 view of the changing compo- "^ 

 sition of nucleus and cytoplasm, i 

 may not be the case at all. < 

 Nevertheless, as a rough ap- 

 proximation the method was 

 useful. Godlevski found great changes in the N.P.R. during matura- 

 tion and segmentation in echinoderm eggs. Each stage has a 

 characteristic N.P.R. : 



Table 164. 



500 

 Number of nuclei 



ibryo 



Fig. 348. 



Thus as the nuclei become more numerous and individually smaller, 

 the total mass of nuclear matter in the whole egg increases enormously. 

 Other good series are those given by Enriques for Aplysia (Fig. 348) , 

 by Bury and by Erdmann. Similar work was done by Conklin. 

 But to summarise all the researches which have been made on the 

 morphological N.P.R. would serve no purpose, for they have already 

 been reviewed in the monographs of Morgan, and of Faure-Fremiet. 



