338 THE CELL 



have to be stored up or contained in one germ. This principle 

 would necessarily follow from the fact, that sexual animals 

 develop in unbroken sequence from one another. Therefore, the 

 natural outcome of the Preformation theory, is the pill-box theory, 

 or, as Blumenbach (IX. 2) expresses it, the theory of the " im- 

 prisoned germs." The eagerness of its supporters actually carried 

 them so far, that they reckoned out how many human germs were 

 boxed up in the ovary of mother Eve, and put down the number 

 as, at the very least, 200,000 millions (Elements der Physiologie, by 

 Haller). 



On the other hand, the theory of Epigenesis in its older form, 

 when worked out more fully, also presents difficulties. For the 

 question suggests itself how nature, with the forces that we know 

 of at her command, can produce in a few days or weeks, out of 

 unorganised matter, an animal organism resembling. its progeni- 

 tors. On this point no theory, which regards the organism as a 

 completely new creation, can supply us with an acceptable and 

 satisfactory solution. 



Blumenbach (XI. 2), therefore, took refuge in the conception of 

 a peculiar " nisus foi-mativus," or formative instinct, which was 

 supposed to cause the unformed or unorganised male and female 

 fluids to assume a " formation," i.e. a definite form, and later on to 

 replace any parts that had been lost. But if we accept the exist- 

 ence of an especial formative instinct, we have obtained nothing 

 more than an empty expression, in the place of an unknown thing. 

 The cell theory, which has been gradually worked out during 

 the latter half of this century, has furnished us with new funda- 

 mental facts, upon which to base more accurate theories of genera- 

 tion and heredity. These facts are, first, that ova and spermatozoa 

 are simple cells, which free themselves from the parent organism 

 for the purposes of reproduction, and that the developed organisms 

 are only organised combinations of a very large number of such 

 cells, which are able to function in various ways, and which are 

 produced by the repeated division of the fertilised egg-cell. A 

 second, and still more advanced principle, is, that the cell in it- 

 self is an extremely complex body, that is to say, that it is an 

 elementary organism. Thirdly, we have gained a fuller know- 

 ledge of the process of fertilisation, of nuclear structure and 

 nuclear division (longitudinal division and arrangement of the 

 nuclear segments), whilst the discovery of the fusion of the egg 

 and sperm nuclei, of the equivalence of the male and female 



