Starting from the discovery of Vernon, that the hybrids of sea-urchins are of different types according to the season, Herbst[132] was able to show that differences among the hybrids with regard to their being more of the paternal or more of the maternal type, are in part certainly due 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[133] 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. [132] *Arch. Entw. Mech.* 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. [133] Only the nucleus of the egg had entered its first stages of activity. What is shown, in the first place, by these discoveries is the importance of an arranging and ruling factor in spite of all units. The organism is always one *whole* whether the paternal properties prevail or the more complicated maternal ones; in other words, all so-called properties that consist in the *spatial relations of parts* have nothing to do with “units” or “allelomorphs,” which indeed cannot be more than necessary means or materials, requiring to be ordered. As to the character of the morphogenetic single and separate units themselves Herbst is inclined to regard them as specific chemical substances which unite correspondingly during nuclear conjugation, forming a sort of loose chemical compound. It would depend on the constitution of this compound whether germ-cells of hybrids could become pure or not. THE RÔLE OF THE NUCLEUS IN INHERITANCE