APPENDIX. 51 



the substance of a mature organism which does not 

 possess the capability of further development, and 

 the substance of an egg, which does possess this 

 capability. By virtue of this difference the egg- 

 substance is characterized as the Anlage, or germ 

 of the mature organism. All characteristics of the 

 adult condition are potentially contained in the 

 ovum." 



Nageli was not the first to assume the existence 

 of a unit of organization intermediate between the 

 molecule and the cell. E. B. Wilson, in his The 

 Cell in Inheritance and Development, states the case 

 as follows: 



"That the cell consists of more elementary units of organiza- 

 tion, is indicated by a priori evidence so cogent as to have 

 driven many of the foremost leaders of biological thought into 

 the belief that such units must exist, whether or not the 

 microscope reveals them to view The modern conception of 

 ultra-cellular units, ranking between the molecule and the 

 cell, was first definitely suggested by Briicke in 1861. 



"This idea of ultra-cellular units is common to most mor- 

 phologists and physiologists. We are compelled by the most 

 stringent evidence to admit that the ultimate basis of living 

 matter is not a single chemical substance, but a mixture of 

 many substances that are self -perpetuating without their loss 

 of specific character."* 



Nageli's Laws of Evolution are also worth special 

 notice. As stated in the body of Abstammungslehre 

 they are as follows : 



i. Asexual reproductive cells which arise by 

 division, remain united and become tissue cells. 



*For a fuller discussion of the notion of these hypothetical units of 

 organic existence, see Weismann's Germinal Selection, (Open Court Pub- 

 lishing Co., Chicago, 1896), especially the foot note, page 230. 



