v GENERATIVE SYSTEM OF THE FEMALE 201 



but serves only to emphasise the fact that it is inexplicable by 

 natural laws. 



The modern views about generation, the constitution of the 

 germ as a sketch of the adult organism, its rapid development, 

 and the inheritance of the parental characteristics in the offspring, 

 are based upon the cellular theory formulated by Virchow towards 

 the middle of last century, and perfected by degrees up to the 

 present time. On the basis of the cellular theory, it is admitted 

 at the present time : (a) that the ova and spermatozoa are cells 

 detached from the organism for the purpose of reproduction, and 

 that adult organisms themselves are only associations, well 

 arranged and connected, of numerous cells transformed, and 

 adapted according to the principle of division of labour for 

 different functions, but all proceeding from the division, millions 

 of times repeated, of the cells derived from the fertilised ovum. 



(J) That the cell is not a substance without organisation, 

 but a very complex structure which constitutes by itself an 

 elementary organism, capable of living in its natural surroundings, 

 independently or associated with others. 



(c) That the cell represented by the fertilised ovum is the most 

 complex cellular structure of the higher animals, that is, the 

 element which has an internal organisation perfectly comparable 

 to that of the organism which is developed from it. 



(d) That the foundations of the theory of generation and 

 heredity must be sought in the knowledge already gained, and to 

 which we have referred in connection with the process of fecunda- 

 tion, the structure and division of the nucleus of the ovum, the 

 maturation of the two sexual elements, the fusion of the male 

 with the female pronucleus, the equivalence of the male and 

 female pronuclei in the fecundation of the mother cell, and 

 their division in the daughter cells. 



The modern theories of generation and heredity are bound up 

 with the names of C. Darwin (1879), Spencer (1876), Niigeli 

 (1884), 0. Hertwig (1884), Strassburger (1884-88), Weismann 

 (1883), and de Vries (1889). In their views the sharp antithesis 

 between the two old theories of ^reformation and epigenesis is in 

 great part reconciled ; they are in fact intermediate between the 

 two, and represent a perfecting of each. For a minute knowledge 

 of these theories I refer the reader to the original works. I will 

 limit myself here to observe that whatever may be the differences 

 between them on accessory particulars, they agree in essential 

 points, on which alone we shall dwell briefly. 



To account for reproduction and heredity, we are forced to 

 admit the hypothesis that the development of the germ does not 

 consist in a new formation or epigenesis, but rather in the trans- 

 formation of a model or rough sketch into a complete organism, 

 capable in its turn of forming a model similar to that from which 



