THEORIES OF PRE -FORMATION AND ENCASEMENT. 35 



Chick, with all its parts pre-formed and wrapped together, 

 and during the development of the incubated egg these 

 parts are merely drawn out and grow. 



As soon as this theory was carried out logically, it 

 necessarily led to the Theory of Encasement. According to 

 this, every species of animal or plant was originally created 

 only as a pair or as a single individual ; but this one indi- 

 vidual already contained, encased within itself, the germs of 

 all the other individuals of its species which have ever lived 

 or will live. As at that time the age of the earth was 

 calculated, according to the Biblical history of creation, at 

 five or six thousand years, people thought they could 

 approximately calculate the number of germs ' of every 

 species of organism which had lived during that period, and 

 consequently the number which had existed encased in the 

 first " created " individual of the species. The theory was 

 logically extended to mankind, and it was accordingly 

 maintained that our first common mother Eve held in her 

 ovary the germs of all the children of men, one encased in 

 the other. 



This Theory of Encasement was then developed so that 

 the fejiiale individuals were considered to be the created 

 beings which were encased one in another. It was believed 

 that only a single pair of each species was originally 

 created ; but the ovary of the female individual contained, 

 encased within it, all the germs of all the individuals of 

 the kind, of both sexes, which were ever to develop. But 

 the Theory of Pre-formation took quite another shape when, 

 in 1690, Leeuwenhoek, the Dutch microscopist, discovered 

 the human spermatozoids, or seminal threads, and proved 

 that a large numbgi? of extremely delicate and actively 



