202 THE PHYSIOLOGY OF REPRODUCTION 



BurchelFs zebra and a number of different mares. These ex- 

 periments were supplemented by others in which animals of 

 various kinds were used. As a result of his investigations he 

 has come to the conclusion that there is no evidence for the 

 existence of Telegony. A microscopic examination of the 

 structure of the hairs of the subsequent foals bred by Pro- 

 fessor Ewart provided further negative evidence. 1 Minot, 2 

 also, in a series of experiments upon guinea-pigs, found no 

 indication of any telegonic influence. Moreover, Karl Pearson, 3 

 as a result of an extensive statistical inquiry, was unable to 

 discover any evidence of telegony in Man. 



ON GAMETIC SELECTION AND THE CONDITIONS FAVOURABLE FOR 

 THE OCCURRENCE OF FERTILISATION 



It is a well-known fact in biology that, as a general rule, 

 conjugation occurs most readily between gametes belonging to 

 the same kind of organism. There are innumerable cases, 

 however, in which the spermatozoa of one species are capable 

 of fertilising the ova of another, and so initiating development. 

 The resulting embryo in such cases may grow into a mature 

 hybrid offspring which is not infrequently sterile (a fact which 

 will be referred to again later), or, on the other hand, owing to 

 some mutual incompatibility in the respective modes of growth 

 inherited from the two parent forms, the embryo may survive 

 for a short time and then perish. 



Cross-fertilisation can usually be induced most easily among 

 closely related species or among varieties belonging to the same 

 species. Thus, the different varieties of the frog, Rana fusca, 

 intercross as readily with one another as each variety fertilises 

 its own ova. On the other hand, the gametes of two species as 

 widely separate as the frog, Rana fusca, and the salamander, 

 Triton alpestris, have been known to conjugate, but the 

 fertilised eggs so produced divided irregularly and consequently 



1 Marshall, "On Hair in the Equidae," Proc. Roy. Soc. Edin., vol. xxiii., 

 1901. 



2 Minot, "An Experiment with Telegony," British Assoc. Reports, Cam- 

 bridge Meeting, 1904. 



3 Pearson, The Grammar of Science, 2nd Edition, London, 1900. 



