2l6 



NATURE 



[November 6, 19 19 



same question, we have also to remember 

 Tanaka's observation that a certain linkage found 

 in the male silkworm is absent in the female. 



Another far-reaching discovery has been made 

 by F. Lillie. When in horned cattle twins^ of 

 opposite sexes occur, the female is sometimes 

 sterile, being called a free-martin. We were 

 inclined to interpret these twins as arising by 

 division of one fertilised ovum, but Lillie, in a 

 study of material from the Chicago stockyards, 

 found that an ovum had dehisced from each 

 ovary, and the twins were therefore originally 

 distinct. Moreover, he showed that in some in- 

 stances the twins have an actual anastomosis in 

 the foetal circulation. We are thus driven to 

 believe that the presence of a male embryo may 

 influence — in cattle — the development of a female 

 embryo, poisoning it, in so far that the develop- 

 ment of the generative organs is partially in- 

 hibited. 



Many complex cases of interaction between 

 factors have been successfully analysed. 

 Punnett's elaborate experiments on the colours 

 of rabbits and sweet peas, Emerson's studies in 

 Phaseolus, and several more such investigations 

 -are gradually laying a solid foundation from 

 which the mechanism of factorial determination 

 may be deduced. The discovery made by,Nilsson- 

 Ehle, and independently by East, that in some 

 forms there are several factors with identical 

 powers, is another notable advance. 



Controversy is proceeding respecting the divisi- 

 bility of factors. When on segregation, either 

 in the gametes of Fj or in later generations, in- 

 stead of two or three sharply differentiated 

 classes of zygotes, much intergradation occurs, 

 or when one of the parental types fails to re- 

 appear, the result may be interpreted either as 

 showing imperfect segregation, or as an indication 

 that the number of factors involved is very large. 



The balance of evidence perhaps suggests that 

 many factors can, and on occasion do, break up 

 (as the sex-factor almost certainly does), some 

 commonly, others exceptionally, while others, 

 again, seem to rnaintain their individuality in- 

 definitely unimpaired. 

 ! As bearing on evolutionary theory, the new 

 work leaves us much where we were. Progress 

 in genetic physiology has been rather a restrain- 

 ing influence. The notion that Mendelian segre- 

 gation applies to varieties and not to species has 

 been often refuted. One of the most useful con- 

 tributions to this subject is Heribert-Nilsson's 

 evidence respecting Salix hybrids. Wlchura 

 ! believed himself to have proved that they and 

 their derivatives are simple intermediates between 

 the parental forms, and this statement, which 

 has passed current for fifty years, is now shown 

 to be a mistake due to insufficient material. In- 

 terest also attaches to Castle's recent withdrawal 

 of his conclusion that by continued selection 

 certain Mendelian characters in rats could be 

 modified, an opinion which, though consistent witii 

 his own experimental work, has not stood a 

 crucial test. We are still without any uncon- 

 trovertible example of co-derivatives from a single 

 ancestral origin producing sterile offspring when 

 ! intercrossed. This, one of the most serious 

 . obstacles to all evolutionary theories, remains. 

 The late R. P. Gregory's evidence that tetraploid 

 Primulas, derived from ordinary diploid plants, 

 I cannot breed with them, though fertile with each 

 I other, is the nearest approach to that pheno- 

 menon, but the case, though exceptionally inter- 

 esting, does not, of course, touch this outstanding 

 difficulty in any way. 



Space does not suffice to enumerate the prac- 

 tical applications of genetic science to economic 

 breeding, of which some have already matured 

 and manv are well advanced. 



TELEGONY. 



Bv Prof. J. Cossar Ewart, F.R.S. 



THE belief in telegony is probably as old as the 

 belief in maternal impressions, so intimately 

 associated with Jacob's breeding experiments, re- 

 corded in the thirtieth chapter of the Book of 

 Genesis. In prehistoric times, when breeds of 

 sheep and cattle brought from the East by the 

 Alpine race were crossed with the more recently 

 formed European breeds striking new varieties 

 would now and again appear. The ancient shep- 

 herds would doubtless endeavour to account for 

 the differences between the cross-bred offspring 

 and their pure-pred ancestors, and later biologists 

 would be called upon to decide which of the views 

 of the ancient breeders were most worthy of sup- 

 port. 



The doctrine of the infection of the germ now 

 known as telegony was more or less firmlv be- 

 lieved in by men of science as well as by breeders 

 NO. 2610, VOL. 104] 



up to the end of the nineteenth century. Beechei-, 

 writing at the close of the seventeenth century, 

 says : " When a mare has had a mule by an ass 

 and afterwards a foal by a horse there are evidently 

 marks on the foal of the mother having retained 

 some ideas of her former paramour, the ass." 

 Agassiz held that the ovary was so modified by 

 the first act of fecundation that "later impregna- 

 tions do not eff'ace that first impression." Similar 

 views were entertained by Haller, Darwin, Herbert 

 Spencer, Carpenter, Sir Everard Home, and 

 others, and up to 1895, when I started my experi- 

 ments, physiologists as a rule either admitted the 

 possibility of the blood of a mare imbibing from 

 that of the foetus some of the attributes which it 

 had derived from its male parent and thereafter 

 handing them on to offspring by a different sire, 

 or believed that some of the unused germ plasm 



