174 



NATURE 



[April 26, 191 7 



would be found filled by S""^^'^' '■> but this difficulty is 

 inherent in all theories which assign the valleys a 

 pre-glacial age. However the glens were 

 formed, they must once have contained river 

 gravels, arjd the fundamental difficulty in the 

 pre-glacial history of Scotland is due to the removal 

 of the earlier gravels during the glaciation. The 

 author objects that by a mistake the view that the 

 Central Valley of Scotland Was a rift valley due to 

 trough faulting has been attributed to him ; but he 

 stated so in the East Lothian memoir (1910, p. 10), 

 referring to the time " when the* Central Vallej' was 

 originated as a structural feature directly influencing 

 the scenery, a true rift valley, in fact, recalling that 

 which at the present day includes the Great Lakes 

 of Africa." 



Within the area of this memoir are many interest- 

 ing igneous rocks and structures, notably the cauldron 

 of Glen Coe. The survey of the area by Mr. Bailey 

 and his colleagues has shown that this formation 



Fig. 2.— An Steall, the waterfall from a hanging valley, tributary to Glen Nevis. Water-worn crags on left due to 

 stream tumbling down marginal crevasse. By permission of the Controller of H.M. Stationery Office. 



was due to the subsidence of a block of ground along a 

 circular fault, up which welled a ring of igneous rocks. 

 The memoir also contains an important contribution 

 to the correlation of the Dalradian rocks of this area. 

 Mr. Bailey explains the difficulties by assuming great 

 recumbent overfolds. His colleague, Mr. Carruthers, 

 on the other hand, adopts a simpler explanation based 

 on a different classification of the rocks. Mr. Bailey 

 recognises that Mr. Carruthers 's interpretation is of - 

 equal standing with his own, which is advanced ten- 

 tatively. It is difficult to judge the arguments with- 

 out the map," the issue of which is delayed by the 

 war. The discussion .as to which of this series of 

 schists is the oldest and which the youngest, and of 

 their true succession, will probably be settled in areas 

 further east, where the problem is simpler, as the 

 rocks have been less disturbed bv the complex earth 

 movements and prolonged igneous activity to which 

 the Ben Nevis district owes so much of its interest 

 and beauty. J. W. Gregory. 



Mn O/ItR \Tr\j nr»"l 



THE GENETICS OF SILKWORMS.^ 



FEW animals lend themselves more readily to breed- 

 ing work than the silkworm moth, and many 

 valuable contributions to our knowledge of their 

 genetics have been made by Japanese workers, among 

 whom Dr. Tanaka has been one of the most success- 

 ful. The present memoir deals with the inheritance 

 of a number of characters. It is in part an amplifica- 

 tion of data previously published by the same author, 

 and in part a collection of new material. Tanaka has 

 dealt for the most part with larval characters. He 

 has worked out in detail the heredity of the patterns 

 peculiar to the various races where his analysis has 

 led him to the detection of seven Mendelian factors. 

 Certain of these are inherited independently, but there 

 are others forming one of those little groups about 

 which there is at present such keen discussion in 

 connection w'ith multiple allelomorphs. In the 

 present case there are four characters belong- 

 ing to the group, viz. 

 striped, moricaud, 

 normal, and plain (or, 

 in the absence of the 

 P factor, striped quail, 

 moricaud quail, quail, 

 and pale quail). As 

 in the other cases of 

 similar nature, either 

 the hypothesis of mul- 

 tiple allelomorphs or 

 that of complete coup- 

 ling covers the facts 

 equally well. 



One of the most 

 interesting of Tanaka*s 

 earlier publications 



dealt with the pecu- 

 liar relation existing 

 between the factor for 

 yellow cocoon and 

 certain factors for 

 larval pattern. In the 

 present .paper this re- 

 lation has been worked 

 out in great detail, 

 and has involved the 

 breeding of more than 

 100,000 individuals. 

 Briefly, the results are 

 as follows : The factor 

 for yellow shows link- 

 age with any one of 

 the group of four 

 characters mentioned 

 above. In the female, linkage is complete, e.g. 

 a female ex yellow striped x white normal forms 

 yellow striped and white normal ova only, 

 while a female ex white striped x yellow normal 

 forms only white striped and yellow normal ova. In 

 the male, however, the linkage is partial. The 

 majority of the sperms are of the two parental types, 

 but about one-quarter belong to the two other possible 

 combinations. Thus a male ex moricaud yellow x 

 striped white forms the four types of gamete, mori- 

 caud yellow, moricaud white, striped yellow, and 

 strii>ed white, nearly in the proportion 3 :i :i :3. 



In Drosophila, as is well known, a similar relation 

 exists between sex and certain characters, but here it 

 is always the male which shows complete, and the 

 female partial, linkage. The significance of the 

 parallel is brought out when it is remembered that in 



1 "Genetic Studies on the Silkworm " By Yo<;himaro Tanaka. Journal 

 uf the College of Agriculture, Tohoku Imperial University, Sapporo. Japan, 

 vol. vii., part 3, June, 1916. Pp. 125-256-f plates i-vi. 



