30 GENESIS OF MAN. 



germ-cells of higher organisms, the deduction is warranted that all 

 higher creatures are the descendants of some form of these unicel- 

 lular beings. Considering the differences that may and do exist 

 even in cells, and in animals consisting of a single cell, Haeckel 

 is led to the conclusion that of all the unicellular creatures known 

 to science, the Amoeba bears the strongest evidence of being the 

 original progenitor of the human race. 



The history of the discovery of the human ova and spermatozoa 

 deserves a brief notice. In 1672, De Graaf discovered the Graafian 

 vesicle, which he supposed to be the ovum itself. In 1797, Cruik- 

 shank, Prevost and Dumas found and described the true ovules, 

 but failed to comprehend their real nature and importance. It was 

 left for Von Baer, thirty years later, to complete the discovery, and 

 place it before the world in its full light. Piirkinje (1825) and 

 Wagner (1835) added important contributions in the discovery of 

 the germinative vesicle or nucleus, and the germinative dot or nu- 

 cleolus. The fact that the ova are simple cells could not be recog- 

 nized until after the founding of the universal cell-theory by 

 Schleiden (1838) and Schwann (1839). It was then perceived that 

 eggs themselves are cells, differing in scarcely any respect from the 

 cells of other tissues. 



The discovery of the spermatozoa, or male seminal animalcules, 

 was first made by Leeuwenhoek in 1674, and confirmed by Louis 

 Ham in 1677. A long war arose between the so-called Animalcu- 

 lists and Ovulists, the first of which believed that the animalcules 

 were the true and only germs of the future being, which simply 

 found in the ova a suitable matrix for their development, while the 

 latter maintained that the ova were the true germs, which were 

 only affected with a germinative impulse by contact with the sper- 

 matozoa. The real nature of this mysterious process has only 

 been clearly brought to light by the labors of more modern inves- 

 tigators, among the foremost of whom must be ranked Prof. Ernst 

 Haeckel, of Jena. 



The ova of all mammals are identical in all essential character- 

 istics. They all possess both nucleus and nucleolus, are of a 

 spherical form, and about one-tenth of a line in diameter, and all 

 acquire at maturity a membranous envelope called the chorion or 

 zona pellncida. The egg of a mouse and that of an elephant can- 

 not be distinguished from each other or from the human ovum in 

 any respect. They are all simple cells. 



