lOO 



HODGE. [Vol. VII. 



the nucleus be equally active in the growth of protoplasm for 

 use in functional activity, as well as for cell-division ? 



An experiment of Boveri (7) in confirmation of observations 

 by the Hertwigs (22) throws some light upon functions of 

 the nucleus. The experiment consists in fertilizing a denu- 

 cleated fragment of a sea-urchin's egg with a spermatozoan of 

 another species ; Rauber's (70) experiment, upon toads' and 

 frogs' eggs, repeated upon a form where success was pos- 

 sible. Rauber wished to ascertain the relative influence of 

 nucleus and protoplasm in the determination of species. Boveri 

 carried the experiment far enough to demonstrate that such 

 denucleated fragments developed into pure male-type embryos. 

 That is, the female protoplasm had no influence. It served 

 simply as food matrix in which the male nucleus could develop. 

 If a female nucleus is present in the fertilized fragment, a hybrid 

 is . developed. So that Boveri is confident in concluding that 

 the nucleus alone carries specific characters from parent to off- 

 spring. Watase (83, p. 262), who gives great prominence to 

 the part taken in cell-division by a portion of the protoplasm 

 (archoplastic spheres and filaments), coincides with the above 

 opinion in the following words : " It is now quite generally con- 

 ceded that the nucleus of the fertilized ovum contains all the 

 hereditary characteristics of the parent organisms." 



If, then, a single microscopical nucleus is capable of deter- 

 mining the form, nuclei, and protoplasm of all the cells of an 

 animal, a fortiori, the nucleus should certainly determine the 

 protoplasm of its own cell. The truth of this is seen in the 

 development of any tissue (53, p. 17). At first there is a mass 

 of nuclei with scarcely a trace of protoplasm ; then around each 

 nucleus protoplasm is gradually laid, until, in form, amount, and 

 structure, the adult cell is attained. Whence comes this proto- 

 plasm, if it is not developed from the nuclei .■' What are nuclei 

 doing in solid heaps unless busy making protoplasm } From 

 the role which they play in a developing ovum, it is plain 

 that nuclei are things too vital and active to be Iving around 

 idle. 



This brings us to a principle which should underlie all study 

 of cellular activity. It may be stated in two ways. 



(i) In any specialised tissue, seek for changes due to functional 

 activity in the structures most prominent in the cells of that tissue. 



