230 SUMMARY OF CURRENT RESEARCHES RELATING TO 



glands of iodine-fed tadpoles are larger than the glands of control 

 specimens held by underfeeding at the same body length as those of the 

 iodine-fed series. The follicles of the glands of such iodine-fed larvse 

 contain a much greater colloid mass than the follicles of the controls. 

 Solutions of iodine will bring about metamorphosis in both normal and 

 thyroidless tadpoles in a short time. Iodine is much more active in 

 accelerating metamorphosis than any of its compounds. Next in order 

 of activity are iodoform and potassium iodide. But potassium iodide 

 appears to have no effect. The suggestion — a safe suggestion — is made 

 that amphibian metamorphosis is a result of the interaction of environ- 

 mental agencies, such as iodine and its compounds, with the hereditary 

 factors controlling the growth processes. Surely this is a general 

 formula for all development ; what is new is the recognition of the 

 r61e of iodine. J. A. T. 



Sheep Crosses and New Varieties of Wool, — J. Cossar Ewart 

 (Scottish Journ. Agriculture, 1919, 2, 1-10, 10 figs.). "Up till a year 

 ago, after interbreeding many different kinds of first crosses, there 

 seemed no escape from the conclusion that sheep do not conform to 

 Mendel's law to the same extent as Andalusian fowls and Shorthorn 

 cattle. But a lamb dropped on the Edinburgh University Farm during 

 the last week of May 1918 clearly demonstrated that this view was 

 untenable." A hybrid ewe, a first cross between an imported Afghan 

 fat-tail ram and a Cheviot gimmer, produced a ram lamb which even 

 at birth had all the points one expected to find in a young pure-bred 

 fat-tail. Experiments made with Southdowns and the primitive Soay 

 sheep indicate that it will be possible to establish a breed having the 

 chief characteristics of the first crosses ; that by mating the first crosses 

 with a Southdown ram material could be at once obtained to start a 

 new and vigorous strain of Southdowns ; and that interbreeding first 

 crosses by the same sire leads at once to a decided loss in size and 

 vigour, and to a decided reduction in the market value. The Southdown- 

 Soay wool is remarkable for its strength and quality, and Southdown 

 blackface crosses are very valuable both as regards mutton and wool. 

 It is pointed out that the reddish colour of the fleece of primitive 

 " peat " or " heath " sheep was probably of protective value, making the 

 sheep inconspicuous to the eyes of eagles and ravens and other enemies,. 

 and that the loss of the coarse long" hair forming the outer coat was 

 probably due more to changes in environment than to selection by the 

 ancient herdsmen. J. A. T. 



Superfoetation in Mice. — F. B. Sumner {Biol. Bulletin, 1916, 30^ 

 271-85). In the pocket-mouse, Peromyscus, it was observed that a 

 female may produce a second litter thirteen to thirty-nine days after the 

 preceding one. As no adult male was present, and as the young males 

 of the first litter were quite immature, it seems clear that the ova 

 liberated by the second ovulation must have been fertilized by sperma- 

 tozoa which had remained latent in the female duct. Another possibility, 

 that there was simultaneous fertilization of two sets of ova, and that 

 one set began to develop while the other set were delayed, seems to the 



