RECENT ADVANCES IN SCIENCE 49 



Reagan has conducted a long series of " Experimental Studies 

 on the Origin of Vascular Endothelium and of Erythrocytes " 

 (ibid.). Two distinct rival classes of theories have been put 

 forward on the above question : on the one hand it was main- 

 tained that all vascular-forming tissue grows into the embryo 

 from the yolk-sac, and the second is that such tissue can arise 

 independently in almost any place. At first sight it appears 

 quite an easy point to determine, but experience has shown it 

 to be fraught with difficulties. The present author has over- 

 come these to a large extent by careful and critical operations 

 on growing chick embryos, whereby pieces were isolated before 

 the formation of vascular tissue. His evidence is all in favour 

 of the possibility of the local formation of the tissue ; indeed, he 

 goes so far as to suggest that prevascular tissue may come from 

 more than one germ-layer. 



General. — Pearl has three papers, " The Experimental Modi- 

 fication of Germ-cells," Parts I. and II. (Jour. Exp. Zool. Jan. 

 191 7), Part III. (ibid. Feb. 191 7). and a general discussion of 

 "The Selection Problem" (Amer. Naturalist, Jan. 191 7). The 

 last points out that although Darwin's theory is logically 

 satisfactory, what we want to know is not what can, but what 

 does take place. He points out that the elimination of indi- 

 viduals is sometimes selective but at other times not, and that 

 the evidence in favour of the transmission of such characters 

 as are selected to the offspring is by no means satisfactory. 

 For these reasons he regards selection as not the primary or 

 even the major factor in Evolution. It is insisted that for a 

 satisfactory explanation we must attack not the animal when 

 adult but the germ-cell, and finishes with some pride and much 

 justice by a reference to " that branch of biological science in 

 which America has taken a leading place." 



Other papers include : " Mendelian Factor Differences 

 versus Reaction System Contrasts in Heredity," by Goodspeed 

 and Clausen, Part I. (Amer. Naturalist, Jan. 191 7), Part II. 

 (ibid. Feb.) ; " The Personality, Heredity, and Work of Charles 

 Otis Whitman, 1 843-1910," by Davenport (ibid. Jan.) ; " Note 

 on the Sex of a Tadpole raised by Artificial Parthenogenesis," 

 by Gatenby (Jour. Micro. Sci. vol. lxii. Feb. 191 7) ; "A Re- 

 examination of the Applicability of the Bunsen-Roscoe Law 

 to the Phenomena of Animal Heliotropism " (Jour. Exp. Zool. 

 Jan. 191 7). 

 4 



