674 



SCIENCE. 



[N. S. Vol. XXII. No. 569. 



neering to an accomplished and distinguished 

 engineer as well as to the successful dean of 

 a school of engineering, and that of doctor of 

 agriculture conferred on gentlemen who have 

 done much to promote this great profession. 

 I should like to call attention to the discus- 

 sion before the American Society of Natural- 

 ists at its St. Louis meeting, as reported in 

 Science of May 27, 1904, in which the ques- 

 tion of honorary degrees was analyzed by a 

 number of distinguished speakers, in connec- 

 tion with that of degrees at large. May it not 

 be hoped that the attention of those having it 

 in their power to confer such degrees may be 

 directed once more to the desirability of such 

 differentiation as the University of Illinois 

 has here applied? William Trelease. 



SPECIAL ARTICLES. 

 THE ORIGIN OF BLACK SHEEP IN THE FLOCK. 



The phrase ' Every flock has its black sheep ' 

 connotes the sporadic nature of their appear- 

 ance. They crop out in flocks of breeding 

 ewes and rams that are wholly white. When 

 a quality suddenly arises from parents that 

 have its opposite the probability is that the 

 two opposed qualities follow Mendel's law in 

 inheritance and that the new, filial character 

 is recessive, the parental opposite dominant. 



There are four tests of recessiveness. First, 

 if the germ gland contains the dominant char- 

 acteristic that characteristic, and not the re- 

 cessive, will show in the soma; consequently, 

 the patency of the recessive in the soma of 

 any individual indicates that its germ gland 

 contains only • the recessive quality. Hence, 

 when two recessive individuals are interbred 

 they will produce only recessive oflspring. 



Second, if a recessive individual is mated 

 with a heterogametous individual — i. e., one 

 which because of mixed ancestry, has both 

 dominant and recessive germ cells — fifty per 

 cent, of the offspring should be recessive. 



Third, if two heterogametous individuals 

 be mated, twenty-five per cent, of the offspring 

 should, in the long run, be recessive. 



Fourth, if recessive individuals (having 

 exclusively recessive germ cells) mate with 

 pure dominant individuals (having exclusively 



dominant germ cells) the soma of the hybrids 

 must show the dominant characteristic. 



An opportunity to test the recessiveness of 

 the black coat in sheep is afforded by the 

 ' Sheep Catalogue ' of Dr. Alexander Graham 

 Bell's (1904) flock,' giving the records of 877 

 sheep used or acquired in pedigree breeding by 

 Dr. Bell. We may apply in turn the four 

 criteria. 



First, of twenty offspring both of whose 

 parents were black, nineteen were black. 

 When I discovered this fact I wrote to Dr. 

 Bell concerning the exception (No, 814, white, 

 female), and he was good enough to reply: 



I have examined the original entry of birth of 

 814 and find her reported as wf 4n s born March 

 23, 1898, out of 712 bf 4n s by 626 bm 5n tw:— 

 still-born, weight 2 pounds. This lamb was still- 

 born and was born in March, this means that I 

 did not see the lamb myself for I am not usually 

 at Cape Breton at that time, and there has not 

 been any verification of color. 



Dr. Bell goes on to state that his shepherd 

 has made errors in recording black as white, 

 and vice versa, but these " have been corrected 

 by subsequent examination. In this case, as 

 the animal was still-born, the record rests 

 entirely upon the unsupported statement of 

 the shepherd." We may consequently neglect 

 No. 814 and conclude that all descendants of 

 two black parents are black. This result is 

 in accord with the hypothesis that black is 

 recessive. 



Second, of 51 offspring of a recessive (black) 

 individual that was heterogametous (because 

 a hybrid between a white and a black parent) 

 26 were white and 25 black. This accords 

 with the hypothesis that black is recessive. 



Third, of 47 offspring, each from two hetero- 

 gametous parents, 40 were white and 7 black. 

 In every family but one the proportion of 

 blacks is below the 25 per cent, expectation. 

 The result is not in strict accord with Men- 

 delism, although closely allied with it. There 

 is evidently some modifying factor. It may 



^ Bell, Alexander Graham, 1904, ' Sheep Cata- 

 logue of Beinn Bhreagh, Victoria Co., Nova Scotia : 

 Showing the Origin of the Multinippled Sheep of 

 Beinn Bhreagh and Giving all the Descendants 

 Down to 1903.' 22 pp. Washington, D. C. 



