60 SCIENCE PROGRESS 



become partly transformed into metaplasm, and they seem 

 to lie within the substance of the rods and in the interprismatic 

 tissue. The enamel calcifies by the adsorption of calcium salts 

 into a honeycomb organic gel-formation. 



Other papers include : " Notes on Agoutis, with Descrip- 

 tions of New Forms," " A new Heliophobius from North-eastern 

 Rhodesia," and " The Spalax of the Grecian Archipelago " 

 (Ann. and Mag. Nat. Hist. Oct. 191 7) ; "A new Rat of the Genus 

 Mylomys from the Upper Nile " (ibid. Nov. 191 7) and " Notes 

 on Georhynchus and its Allies " (ibid. Dec. 191 7), all by Thomas ; 

 " On a new Species of Shrew from Corea," by Sowerby (ibid. 

 Oct. 191 7) ; " The Classification of existing Felidce," by Pocock 

 (ibid. Nov. 191 7) ; " A Case of Accessory Lungs associated 

 with Hernia through a Congenital Defect of the Diaphragm," 

 by Gladstone (Journ. of Anat. vol. Hi. Oct. 191 7) ; " Form 

 and Function of Teeth : A Theory of Maximum Shear," by 

 Shaw (ibid.) ; " The Earliest Stages of Development of the 

 Blood-Vessels and of the Heart in Ferret Embryos," by Wang 

 (ibid.)) "Inheritance of Fertility in Southdown Sheep," by 

 Wentworth (Amer. Naturalist, Nov. 191 7) ; " Evidence for 

 the Death in Utero of the Homozygous Yellow Mouse," by 

 Ibsen and Steigleder (ibid. Dec. 191 7) ; " Deformity of os penis 

 in a Phoca caspica Nilsson," by Alpheraky (Proc. Zool. Soc. 

 Nov. 191 7), and " The Structure of the Orbito-temporal Region 

 of the Skull of Lemur," by Wood Jones (ibid). 



General. — An address given by Gates at the Pacific Coast 

 meeting of the American Association for the Advancement 

 of Science is published under the title " The Mutation Theory 

 and the Species Concept" (Amer. Naturalist, Oct. 191 7). Its 

 general conclusions are summarised by the author in the follow- 

 ing words : "I have endeavoured to show that in plant and 

 animal species there are two distinct types of variability, having 

 different geographical relations. The one is discontinuous, 

 independent of environmental or functional influence, and has 

 given rise to many specific and generic characters notably in 

 plants, but also in higher animals. The other is continuous and 

 apparently represents the results of the stress of the environ- 

 ment on the species in its dispersal, leading to the gradual 

 differentiation of local races or sub-species whose peculiarities 

 are ultimately intensified and fixed. The latter type of specia- 

 tion is notably exemplified in birds and mammals, organisms 



