310 THE CELL 



These arrangements are: (1) the distribution of the sexual 

 organs over two different individuals, so that one produces only 

 female sexual cells, and the other only male; (2) the reciprocal 

 fertilisation of hermaphrodite individuals ; (3) the different times 

 at which the maturation of the ova and spermatozoa occurs, as- 

 in Pyrosoma, many molluscs, etc. ; and (4) the peculiarities in the- 

 organisation of hermaphrodite flowers of phanerogams (both dicho- 

 gamy and heterostylism), and the part played by insects, which, 

 in carrying the pollen from one flower to the other, induce cross 

 fertilisation, as has been observed and described by Koelreuter,. 

 Sprengel, Darwin (VII. 8), Hildebrandt (VII. 24), H. Miiller 

 (VII. 49), and others. These arrangements for the prevention of 

 self-fertilisation are so many-sided and striking, especially in 

 flowering plants, that Sprengel was able, in his book, to speak of 

 "the discovered secret of nature, the fertilisation of flowers by 

 insects," and to say : " Nature does not seem to have wished that 

 a single hermaphrodite plant should be fertilised with its own 

 pollen." 



/?. Bastard Formation, or Hybridisation. The opposite 

 of self-fertilisation and in-breeding is hybridisation. By this is 

 meant the union of several products of individuals, which are SO' 

 different in their organisation, that they are classified into different 

 varieties, species, or genera. 



As a rule, the principle, that the sexual products of individuals, 

 which are very different from one another, do not unite with one 

 another, is correct. Everybody considers it impossible for the 

 ovum of a mammal to be fertilised by the spermatozoon of a 

 fish, or for that of a cherry-tree by the pollen of a conifer. But 

 as the individuals become more closely related, whether they 

 belong to different families or species, or even only to different 

 varieties of the same species, the more difficult does it become to' 

 prophesy a priori as to the result of cross-fertilisation. This can 

 only be discovered by means of experiment, which has shown 

 that the various species in the animal and vegetable kingdoms do 

 not always behave in a similar manner towards hybridisation, in 

 that individuals which resemble one another in their form, down to 

 the minutest details, often cannot be crossed, whilst between others 

 which are much more dissimilar bastard fertilisation is possible. 



Briefly, sexual affinity does not always march pari passu with 

 the external similarity which can be perceived between the 

 individuals in question. 



