THE ORGANIC CELL 
11 
mind was obscured by the fallacy of spontaneous generation. 
Neither could he have had any true idea of the nature of the 
egg, for the cellular structure of living things was not under- 
stood until two centuries later. For a century after Harvey’s 
time desperate efforts were made to solve the mystery of the 
origin of the individual life. The extremists evolved what is 
known as the Preformation theory, which taught that the 
germ, whether ovum or sperm, contained a miniature organism, 
already preformed though invisible, which, on becoming 
unfolded, revealed the perfectly developed animal. 
The egg was thus supposed to contain a minute model of 
the chick, which in its turn contained still minuter models 
ad infinitum. One enterprising fanatic calculated that Mother 
Eve must have contained at least 200,000 million homunculi. 
The ‘ Ovists,’ believing that the ovum contained the miniature, 
held fierce discussions with the ‘ animalculists ’ who championed 
the claims of the sperm. 
This long-lived theory of Preformation received its death- 
blow when Caspar Wolff in 1759 demonstrated his theory 
of ‘ epigenesis ’ by which he sought to show that there was 
a gradual development from a simple rudiment to a form of 
greater complexity. Wolff clearly showed in the chick the 
process of development from a simple rudiment, but having 
no idea of the uniqueness of the germ cells, was forced to fall 
back on the postulate of a vis corporis essentialis. 
Thus the external nature of development was determined, 
but the structure of the egg and the process of inheritance 
remained in the dark for yet another century. Schwann and 
his followers, in 1889, established the fact beyond the possibility 
of doubt that the egg is a cell, having the same fundamental 
structure as other cells of the body. Then dawned the striking 
truth that a single cell may contain within itself the sum-total 
of the heritage of the species. It was in regard to the female 
sex that this conclusion was first arrived at ; but the doctrine 
was soon extended to the male as well. Leeuwenhoek in 
1677 showed that the fertilising fluid contained numberless 
minute motile bodies, possessing as a rule very active move- 
ment, and for this reason described by the early observers as 
parasites or infusoria, an idea which caused the origin of the 
