October 25, 1901.] 



SCIENCE 



637 



set of soil analyses, and described a scheme 

 of coloration which might be employed to 

 indicate different qualities of soil. 



THE ZOOLOGICAL SECTION. 



The address of the President of the zoo- 

 logical section. Professor J. Cossar Ewart, 

 was entitled, ' The Experimental Study of 

 Variation,' and was a consideration of the 

 results of experimental breeding in their 

 bearing on the causes of variation and on 

 certain theories which have been more or 

 less generally accepted. Especial interest 

 was given to the address by the fact that 

 the conclusions reached were based for the 

 most part on the results of experiments 

 conducted by the author at his Penycuik 

 station, and the members of the association 

 had the pleasure of studying for themselves 

 three of the now celebrated zebra hybrids 

 which Professor Ewart has bred. 



In opening his address Professor Ewart 

 assumed that the primary cause of varia- 

 tion is always the effect of external influ- 

 ences acting directly upon the germ-cells 

 and proceeded to discuss certain influences 

 which might be supposed to be active in 

 the production of variability. 



1. Age was found to have a decided 

 effect upon the character of the offspring. 

 A young blue-rock male pigeon was mated 

 with a well-matured and vigorous black 

 barb ; the first pair of birds resulting from 

 the mating were almost exactly like the 

 female parent except that the beaks were 

 rather longer ; one of the second brood 

 resembled the barb, while the other was of 

 a grayish color with slightly mottled wings 

 and a tail bar ; in the third brood both 

 birds were of a grayish color with indis- 

 tinct wing bars as well as a tail bar; while 

 in the fourth brood one bird resembled the 

 birds of the third brood, while the other 

 resembled closely its blue rock sire. Simi- 

 lar results were obtained by mating a young 

 blue rock male with a white fantail, and 



also by pairing young gray quarter-wild 

 rabbits with an old white Angora buck, and 

 Professor Ewart regards the gradual, ' al- 

 most mathematical ' change in the colora- 

 tion of the offspring as due to the gradual 

 increase of vigor or prepotency of the 

 young sires. The phenomena might pos- 

 sibly be explained by the doctrine of ' satu- 

 ration ' popular among breeders, but such 

 an explanation is overthrown by the occur- 

 rence of the same results in the crossing of 

 young females with old males. 



2. Ripeness of the germ-cells. In study- 

 ing the effect of this condition the Peny- 

 cuick experiments confirmed the results 

 obtained by Mr. H. M. Vernon from the hy- 

 bridization of Echinoderm ova, 'the offspring 

 resulting from the union of equally ripe 

 germ-cells differing from the offspring de- 

 veloped from the conjugation of ripe and un- 

 ripe germ-cells, and still more from the 

 union of fresh and over- ripe germ-cells.' 



3. The condition of the soma. Un- 

 doubtedly the germ-cells may be influenced 

 by a diminution of the vitality of the soma, 

 but there is no evidence to show that they 

 are modified in such a way as to transmit 

 definite modifications in the offspring. 



4. Change of habitat. This factor acts 

 by influencing the vigor of the soma, but 

 ' there is no evidence whatever that definite 

 changes of the soma, due to the direct 

 action of the environment, can be imprinted 

 on the germ- cells.' 



5. Intercrossing and interbreeding. In- 

 tercrossing in general tends towards rever- 

 sion and never results in the production of 

 characters absolutely new to the species. 

 It may, however, indirectly tend towards 

 progressive variation by imparting addi- 

 tional vigor to the offspring, which when 

 intercrossed frequently give rise to ' an 

 almost infinite diversity of character.' In- 

 terbreeding, on the other hand, may be a 

 cause of progressive variation. Vigor, how- 

 ever, plays a very important part in the de- 



