THE GERM-CELLS 29 



protoplasm and nucleus. It was only after the discoveries 

 of Schleiden and Schwann, and the application of the cell- 

 theory to the whole range of biological facts, normal as well 

 as pathological, that a real science of life became possible. 



This being the case with biological science in general, it 

 is not astonishing that the same applies with even more 

 force to the science of Heredity. The latter can, indeed, 

 be said to date in reality only from the time of the dis- 

 covery of the cell-nature of both sexual germs, the ovum 

 and spermatozoon. 



The chick had gradually been traced back (by Harvey 

 1651, Malpighi 1672, and others) to its real starting-point 

 the vital part within the hen's egg ; but it was as late as 

 1828 that Von Baer discovered the ovum of the mammals. 

 It was much later still in 1861 that the German zoologist 

 Gegenbaur finally demonstrated the fact that the egg of 

 every vertebrate is a single cell, the same being subse- 

 quently shown to hold good for that of invertebrates and 

 plants also. 



The male sex-element of the higher animals, not being 

 permanently hidden within the body, as is the egg-cell, was 

 discovered very much earlier in 1677. But here the 

 central fact was at first missed altogether : the seminal 

 fluid was thought to be the important element, while the 

 spermatozoon was looked upon, as the name implies, as 

 a parasitic animalcule. It was only much later that the 

 presence of spermatozoa was found to be the essential 

 factor in fertilization, and only in 1841 did Kolliker demon- 

 strate its cellular origin in the male sex-glands, the testes. 



II. THE GERM-CELLS. 



It is, then, a fundamental fact that both germ-cells, the 

 ovum as well as the spermatozoon, are single cells, pos- 

 sessing all the qualities of such, and behaving in their 

 fundamental functions like cells. These we are now going 

 to study more in detail. 



