232 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



and its exceptions, founded, that is, upon a study of the 

 " second " generation of hybrids, there is another important 

 line of research lately inaugurated by Herbst, which in- 

 vestigates the first generation in hybridisation. The hybrids 

 themselves are studied with the special purpose of finding 

 out whether the type of the single hybrid may change 

 according to the conditions of its development, both outer 

 and inner. The discoveries thus made may lead some day to 

 a better understanding of the intimate nature of the " units " 

 concerned in heredity, and perhaps to some knowledge of 

 the arranging and ruling factor in morphogenesis also. 



Starting from the discovery of Vernon, that the hybrids 

 of sea-urchins are of different types according to the 

 season, Herbst l was able to show that differences among 



' O 



the hybrids with regard to their being more of the paternal 

 or more of the maternal type, are in part certainly clue to 

 differences in temperature. But there proved to be still another 

 factor at work, and Herbst has succeeded in discovering this 

 factor by changing the internal conditions of morphogenesis. 

 Whenever he forced the eggs of Sphaerechinus to enter into 

 the first 2 phase of artificial parthenogenesis and then fertilised 

 them with the sperm of Echinus, he was able to approximate 

 the offspring almost completely to the maternal type, whilst 

 under ordinary conditions the hybrids in question follow 

 the paternal far more than the maternal organisation. 



What is shown, in the first place, by these discoveries 



1 Arch. Entw. Mec7i. 21, 22, and 24, 1906-7 ; see also Doncaster, Phil. Trans. 

 Royal Soc. London, B. 196, 1903. The influence of different temperature 

 upon the organisation of the hybrids is not always quite pure, inasmuch as 

 the paternal and the maternal forms may themselves be changed by this agent. 

 In spite of that there exists an influence of the temperature upon the hybrid 

 as such, at least with regard to certain features of its organisation. 



' 2 Only the nucleus of the egg had entered its first stages of activity. 



