564 SUMMAEY OF QUERENT RESEARCHES RELATING TO 



paper by 0. Schultze* on the origin of double monstrosities. This 

 result may follow from three possibilities : — (a) The ovum escapes from 

 the ovary with two nuclei, and may be fertilised by two spermatozoa, 

 from which two processes of segmentation would follow. (6) Through 

 over-ripeness, the innate tendency to division on the part of the ovum 

 may lead to its division into two parts, each of which may subsequently 

 be fertilised, (c) The ovum may be normally fertilised and proceed to 

 the first division. Then, by some unknown process, each of the first 

 two blastomeres may go on to an independent development. 



Homogamy and Fertility.f — Prof. Karl Pearson, some time ago, 

 asked the interesting question : — " When any form of life breaks up 

 into two groups under the influence of natural selection, what is to 

 prevent them intercrossing and so destroying the differentiation at each 

 fresh reproductive stage ? " The answer, he suggested, was twofold — 

 (1) homogamy [i.e. mating of like with like], which he demonstrates to 

 exist in the case of man ; and (2) a possible dependence of fertility on 

 homogamy, which would render the cross-unions relatively sterile. His 

 view was, that a correlation of homogamy with fertility, together with 

 natural selection, could produce a permanent differentiation of species, 

 but that neither alone could be effectual. 



After giving evidence that a progressive change, but no differentia- 

 tion, can be produced by reproductive selection, he discusses the whole 

 theory of the influence on evolution of a relation between homogamy 

 and fertility. Reproductive divergence has not an effective existence. 

 " So far as I can yet see, differentiation must involve natural selection, 

 and one can only appeal to reproductive selection as a means, but I think 

 an effective means, of maintaining a differentiation already brought about 

 by Darwin's fundamental factor in evolution." 



Secondary Sexual Characters.^ — Mr. G. E. H. Barrett-Hamilton 

 says that no attempt, so far as he knows, has been made to trace the 

 primary physiological meaning, as apart from secondary utility, of these 

 characters. He thinks, as many have thought, that " there must be some 

 widespread and fundamental causes to which all owe their origin." A 

 clue has suggested itself to him in his study of the nuptial changes of 

 the anadromous salmonoid genus Oncorhynchus, whose spawning he ob- 

 served in Kamchatkan waters. The nuptial changes of form and 

 coloration occur in both sexes, and the fish when thus affected are most 

 obviously out of condition. They are, indeed, in a pathological state. 

 It is said that one species only, 0. orientalis, survives the spawning, 

 and this is one of the species which becomes least distorted and dis- 

 coloured. In a pathological state, induced by the influence of the gonads 

 on the general metabolism, he finds the starting point whence " natural 

 selection by alteration, suppression, or accentuation of the details, might 

 easily produce many or all of the nuptial changes of animals as we 

 now see them." 



Segmentation of Vertebrate Head.§ — Mr. Charles Hill now pub- 

 lishes in full his paper on this subject, with an introductory review of 



* Ziegler's Centralbl. f. Pathol., x., Heft 10. 



t Proc. Roy. !Soc. London, lxvi. (1900) pp. 316-23. 



% Proc. Cambridge Pliil. Soc, x. (1900) pp. 279-85. 



§ Zool. Jahib. (Abt. Anat.), xiii. (1900) pp. 393-446 (3 pis. and 4 figs.). 



