720 



SCIENCE 



[N. S. Vol. XXXVI. No. 934 



found that the percentage of " crossing-over " 

 in the female is 21.9. 



These experiments make clear, first, that 

 there is no crossing-over in the male (at least 

 for the number of cases here recorded) ; sec- 

 ond, that in the female the gametic ratio is 

 aiout one to four. 



The bearing of the results on the explana- 

 tion of the absence of crossing-over of sex- 

 linked characters in the male is obvious. In 

 that case the presence of only one sex chromo- 

 some in the male made crossing-over impos- 

 sible, and this was the explanation offered. 

 But the factors concerned v^ith black and 

 wingless lie in a different chromosome (in the 

 sense that they are linked to each other and 

 not to any sex-linked factor) which is present 

 in duplex in both sexes, yet crossing over oc- 

 curs in one sex only. Whether this second 

 chromosome is the one to which in Drosophila 

 the sex chromosome is attached can not be 

 stated, and the question must be left unsettled 

 until we have tested the crossing-over of 

 other factors in this and in other chromo- 

 somes. 



As Mr. A. H. Sturtevant has pointed out 

 to me, the case here recorded offers appar- 

 ently an explanation of cases in plants recently 

 described by Bateson and others.^ When the 

 two dominants enter from different sides no 

 crossing over is apparent, as seen in the first 

 case recorded above ("complete repulsion"). 

 When the two dominants enter from the same 

 side there is evidence of crossing over (" par- 

 tial coupling"), as shown by the following 

 example. Gray, winged females were mated 

 to black, wingless males, and gave gray, 

 winged Fj offspring. These inbred produced 

 the following F^ classes : 



BW 



GW 



246 



Bw 

 65 



Gw 

 18 



These results in the F, generation are of the 

 same kind as those that Bateson and Punnett 

 have recorded for peas, etc. Back-crossing 

 has shown in the flies that the results are due 

 to failure of " crossing-over " in the males. 

 If the same tests, when applied to peas, give 



'Proc. Eoy. Soc, Vol. 84, 1911. 



the same result there will be no longer any 

 need to assume, as Bateson and Punnett have 

 done, that there is (A) a system of partial 

 coupling, (B) a system of complete repulsion, 

 or " spurious allelomorphism " or to assume 

 (G) a system of special dichotomous ratios 

 for coupling, such as 3 : 1 and Y : 1, etc. 



T. H. Morgan 



THE PROBABLE RECENT EXTINCTION OF THE 

 MUSKOX IN ALASKA 



The question of the probable recent extinc- 

 tion of the muskox {Ovibos moschatus) in 

 northern Alaska, which has often been mooted, 

 acquires new interest through information 

 kindly furnished me by Mr. Vilhjalmur 

 Stefansson, who has just returned from four 

 years of exploration in Arctic America in the 

 interest of the American Museum of Natural 

 History. Under date of New York, Novem- 

 ber 2, 1912, he writes : 



Dear Dr. Allen: At your request I summarize 

 briefly my information in regard to muskoxen in 

 Alaska secured on the museum's arctic expedition 

 during the years 1908-12; a full statement will 

 in due course be prepared by Mr. R. M. Anderson, 

 who was in charge of the zoological work of the 

 expedition. 



(a) Information secured from natives and white 

 residents in Alaska: During the winter 1899-1900 

 there died at Cape Smythe (or near there) the 

 Eskimo man called Mangi by the whalers (prob- 

 ably Mangilanna). He was the last to die of Gape 

 Smythe (Point Barrow) natives who had seen live 

 muskoxen in that vicinity. He was probably born 

 between 1845 and 1850, as he was able to remem- 

 ber Maguire's visit to Point Barrow. A few years 

 after Maguire's time — perhaps therefore about 

 1858 — ^there was scarcity of food in winter at Cape 

 Smythe. Mangi 's father then went inland looking 

 for caribou, and some distance up the Kunk River, 

 which flows into Wainwright Inlet, they fell in 

 with a band of thirteen muskoxen and killed them 

 all. Since then no one near Point Barrow is 

 known to have killed muskoxen or seen them. 



There are many places inland from Point Bar- 

 row where muskox skulls and bones are abundant. 

 As these are heavy and there is no market for 

 them locally, few are brought to the coast. Our 

 party secured one skull only. 



(b) Information based on specimens: While dig- 



