SOME PROBLEMS OF REPRODUCTION. 591 



the semen raiist actually come in contact witli the egg. By 

 the midflle of the last century the change was recognised in 

 all well-studied instances as due to the entrance of a sperm 

 and its complete fusion with the egg. 



During tlie last three decades of the century it was shown 

 that the sperm is itself a cell, and that the fusion is a complete 

 one, cytoplasm to cytoplasm and nucleus to nucleus, so that 

 the germ begins life as a simple 1-nucleate cell, which we 

 term the ''oosperm," the equivalent of the "fertilised egg'^ of 

 common speech. The latter term is falling into disuse from 

 its undue exaggeration of the share of the egg; and is the 

 more to be deprecated as the process is known to be in 

 essence identical with other fusions, known as "isogamous" 

 or "equal conjugations," where the two pairing-cells are 

 similar to the point of identity. 



Meanwhile, within the last four or five years, through the 

 revival, principally by Jacques Loeb, of lines of research 

 initiated a decade earlier by the brothers Hertwig, it was 

 found that by treatments of the most varied kinds (mechanical, 

 osmotic, chemical) the eggs of certain Metazoa could be 

 induced to develop without the intervention of the sperm — 

 this result was too rashly called " artificial fertilisation," and 

 was still more rashly invoked as the clue to the meaning of the 

 fusion process which constitutes "fertilisation" in its actual 

 derived sense. Indeed, the lay press was full of marvellous 

 accounts of " chemical fertilisation," for which, perhaps, the 

 enthusiastic professors of the Chicago School are hardly to be 

 .held responsible. Yet, as we have seen, this was no misuse 

 of the term in its two older senses — the egg, hitherto infertile, 

 became fertile under the treatment, and started as a germ into 

 a new life. But that sense had become so entirely obsolete 

 that now by common consent we apply to all these cases the 

 uncontroversial term "artificial" or "induced partheno- 

 genesis." 



We must remember that in many groups of animals the eggs 

 (or cei'tain types of them) can develop Avitliout any co-opera- 

 tion of the sperm ; and, indeed, this often occurs in the 



