Vererbung, Variation, Mutation. 453 



uiifertilized. A day later (a) had produced many larvae, (b) liad neither develo- 

 ped nor undergone cytolysis, though surrounded by "forests of spermatozoa" ; 

 (c) also remained unclianged. It follows, therefore, that the cytolysis is due to 

 the entrance of foreign spermatozoa, and probably the excessive mesenchyme 

 formation is akin to cytolysis. Further, by lying in sea-water foraday the eggs 

 became unreceptive to foreign spermatozoa, although capable of normal fertili- 

 zation by their own species. Doncaster. 



1199) Shearer, C, De Morgan, W. and Fuchs, H. M., On the experimen- 

 tal hybridization of Echinoids. In: Phil. Trans. Royal Soc, Bd. B204, 

 Nr. 310, S. 255—362, 7 PI., 1914. 



In this long paper the authors sum up the results of four years' work on 

 hybridizing the British species of Echinoids, of which several preliminary re- 

 ports have already appeared. A complete summary of the work is not possible 

 in a Short space; only the authors' general conclusions can be given. The chief 

 difference between their methods and those of other investigators is that the 

 authors have studied especially the characters of the later larvae and metamor- 

 phosed urchins, which have much more definite specific features than the early 

 larvae. The species used were Echlnus esciäenius, E. acutus, and E. miliaris; all 

 possible crosses were made between them. The characters chiefly considered 

 were the posterior ciliated epaulettes and the green pigment masses, the former 

 characteristic of E. esculentus and E. acutus, and absent in E. miliaris; the latter 

 present in miliaris and absent in the other two species. In general, esculentus 

 and acutus are very closely alike, and their larvae are hardly separable, so that 

 the experiments deal chiefly with crosses between them and miliaris. Another 

 less constant character of which the inheritance is considered is the posterior 

 pedicellaria of the late larva of acutus and esculentus, which is usually present in 

 these species, never in miliaris. 



The most important result obtained was that in the three years 1909 — 1911 

 the inheritance of these three characters was always only through the maternal 

 parent; reciprocal crosses were unlike, miliaris § X acutus er esculentus cT giving 

 plutei with green pigment but no posterior epaulettes nor posterior pedicellariae ; 

 acutus or esculentus $ X miliaris S' giving larvae with posterior epaulettes and 

 usually pedicellariae, but no green pigment. In 1912, however, these results were 

 partially reversed, most of the larvae fonn miliaris $ being paternal in character, 

 but a few cultures mixed. The crosses with acutus and esculentus $ in 1912 remained 

 as in previous years, so that in 1912 the characters of these species were dominant 

 in both reciprocal crosses. That the maternal inheritance of the previous years 

 was not due to pseudogamy is indicated by the cytological examination of the 

 material by Doncaster and Gray, and the authors, after reviewing the literature 

 of other comparable cases, seek to discover the cause of the change. It cannot 

 be due to temperature during larval development, nor to the stage of ripeness of 

 the eggs, since it was independent of season. It is concluded that it must be 

 due to changes affecting the eggs in the ovary of miliaris possibly during the 

 preceding winter. That the change is dependent on the miliaris females is sug- 

 gested by the following facts: (l) only crosses with miliaris $ were affected; 

 (2) cultures of pure miliaris were much less easy to obtain in 1912 than in pre- 

 vious years; (3) rarely more than 20 percent of the miliaris eggs developed when 

 fertilized by sperm of acutus or esculentus, while in preceding years 80 — 90 per- 

 cent developed; (4) it was in the cultures (1912) in which the highest pro- 



