Januaey 23, 1920] 



SCIENCE 



79 



no way committed to any interpretation. 

 Stated negatively we might add that there is 

 nothing known at present to preclude the 

 possibility that the influence is a purely chem- 

 ical process. We find ourselves, therefore, 

 practically in agreement with Whitman's atti- 

 tude when he says : 



" N'ow while ontogeny is so wonderfxdly ex- 

 act that we never cease to be amazed at its 

 performances, we must not forget that germ- 

 cells are subject to slow variation. In fact, 

 it is only germ-variation that has to be con- 

 sidered in phylogeny as in ontogeny. Conse- 

 luently, when the germ-cell takes a step for- 

 ward, ontogeny begins with an initial differ- 

 ence that sets the whole series of ontogenetic 

 stages on a diverging line that digresses so 

 little as to be undiscoverable until nearly at 

 the end of development."^ 



Whitman's failure to find " dominance and 

 recessiveness " of character in his pigeon 

 crosses led him to attack the supposed im- 

 portance of these relations. To-day we know 

 more cases where the hybrid shows in some 

 degree an intermediate development of the 

 contrasted characters than where dominance 

 is complete Obviously the distinction has no 

 importance since the law of segregation is 

 found to hold as well when blending occurs 

 as in cases where the somatic differences are 

 clearly evident. The hybrid pigeons fall, 

 therefore, in this respect into line with 

 familiar phenomena. The failure of " split- 

 ting" in subsequent generations is a i)oint 

 that calls to-day for special consideration, 

 but will not be dwelt on here. 



In this chapter, and in several that precede 

 it, Whitman and the editor speak rather 

 frequently of what is called " weak " and 

 " strong " germs as having an imi)ortance in 

 determining the " strength " to which a char- 



3 The reviewer would add an important reserva- 

 tion, viz., that a "forward step" in the germ- 

 plasm might affect any stage in the course of de- 

 velopment, or in the extreme case every stage in 

 the development. This view is obviously consistent 

 with what Whitman states, but, if emphasized, 

 would to a large extent undermine the value of the 

 evidence from ontogeny in interpreting ancestral 

 ttages. 



acter develops, even causing a " reversal of 

 dominance." Curiously enough their effects 

 are supposed to be transmitted so that fertility 

 in the offspring is also affected. Even the 

 occasional mutations found by Whitman are 

 ascribed to this source. Pigeons unquestion- 

 ably fTornish unusual material for the study 

 of this appearance. It is perhaps too soon to 

 attempt to state how much or how little in 

 variation to ascribe to such an influence, aside 

 from the obvious effect in the immediate off- 

 spring. 1^0 doubt further work along these 

 lines will help us to define more sharply what 

 is to be understood by the somewhat vague 

 attributes " weakness " and " strength." 



There are important discoveries recorded 

 in this volume that can only be referred 

 to briefly; the "divisibility" of characters 

 (meaning intermediate conditions) as seen in 

 hybrids, the study of a " dominant " mutant 

 character; the discovery as early as 1896 of 

 sex-linked inheritance (of which a number of 

 cases in other birds are well understood to- 

 day), the cross between the last surviving 

 members of our wild passenger pigeon and the 

 ring dove, the relative influence of egg and 

 sperm on the time of hatching of the hybrid 

 young. Each of these results marks an ad- 

 vance in our understanding of heredity. 



The third volume containing Whitman's ob- 

 servations on the " Behavior of Pigeons " is 

 edited by Professor Harvey A. Carr. Thirty- 

 two short manuscripts were left. It appears 

 that Whitman's first period of study in this 

 field was from 1895—98. In a few lectures at 

 Woods Hole in 1897-98 some of his conclu- 

 sions are given. After a period of five years 

 a renewed interest in these directions recui-red 

 and many notes were made. The Woods 

 Hole lecture in 1906 gave an opportunity for 

 further consideration. Despite the very frag- 

 mentary remains of this work — fraginentary 

 only in comparison with the extensive obser- 

 vations that Whitman had made, this volume 

 contains many observations of great interest 

 and gives an insight into the character of 

 Whitman's methods, where the most careful 

 and minute observations are interpreted with 

 a breadth of intelligence that is truly remark- 

 able. There are few if any groups of animals 



