Apkil 2S, 1916] 



SCIENCE 



611 



tain an abundant fossil fauna, largely of ma- 

 rine molluscs. The Sasicava formation in- 

 cludes beach gravels which are found at 27 

 different levels of general importance so far as 

 the island is concerned. The highest of these 

 is at an altitude of 617 feet above tide. Post- 

 glacial movements are represented by minor 

 faults and folds as well as by the continental 

 deformation which altered the shore-lines of 

 the Champlain sea. The latter is attributed to 

 isostatic adjustment consequent upon the re- 

 moval of the ice-load. 



KiKTLEY F. Mather 

 Queen's University, 

 Kingston, Canada 



SPECIAL ARTICLES 



THE THEORY OF THE FREE-MARTIN 



The term free-martin is applied to the fe- 

 male of heterosexual twins of cattle. The 

 recorded experience of breeders from ancient 

 times to the present has been that such fe- 

 males are usually barren, though cases of nor- 

 mal fertility are recorded. This presents an 

 unconformable case in twinning and sex-de- 

 termination, and it has consequently been the 

 cause of much speculation. 



The appearance of an abstract in Science^ 

 of Leon J. Cole's paper before the American 

 Society of Zoologists on " Twinning in Cattle 

 with Special Reference to the Free-Martin," is 

 the immediate cause of this preliminary report 

 of my embryological investigation of the sub- 

 ject. Cole finds in a study of records of 303 

 multiple births in cattle that there were 43 

 cases homosexual male twins, 165 cases hetero- 

 sexual twins (male and female), and 88 cases 

 homosexual female, and 7 cases of triplets. 

 This gives a ratio of about Id'd' : 4c?? : 25?, for 

 the twins instead of the expected ratio of 

 1:2:1. Cole then states : 



The expectation may be brought more nearly 

 into harmony with the facts if it is assumed that 

 in addition to ordinary fraternal (dizygotic) 

 twins, there are numbers of "identical" (mono- 

 zygotic) twins of both sexes, and that while in the 

 case of females these are both normal, in the case 

 of a dividing male zygote, to form two individ- 



1 Vol. XLIIL, p. 177, February 4, 1916. 



uals, in one of them the sexual organs remain 

 in the undifferentiated stage, so that the ani- 

 mal superficially resembles a female and ordi- 

 narily is recorded as such, although it is barren. 

 The records for monozygotic twins accordingly 

 go to increase the homosexual female and the 

 heterosexual classes, while the homosexual male 

 class in which part of them really belong, does not 

 receive any increment. 



Cole thus tentatively adopts the theory, 

 which has been worked out most elaborately by 

 D. Berry Hart, stated also by Bateson, and im- 

 plied in Spiegelberg's analysis (1861), that the 

 sterile free-martin is really a male eo-zygotic 

 with its mate. 



Cole's figures represent the only statistical 

 evidence that we have on this subject. Let us 

 follow his suggestion and take from the hetero- 

 sexual class enough cases to make the homo- 

 sexual male twins equal in number to the 

 homosexual female pairs ; this wiU be approxi- 

 mately one fourth of the class, leaving the ratio 

 2:3:2 instead of 1 : 4 : 2. Which one of these 

 is the more satisfactory sex ratio I leave 

 others to determine; I wish only to point out 

 the fatal objection, that, according to the 

 hypothesis, the females remaining in the 

 heterosexual class are normal; in other words, 

 on this hypothesis the ratio of normal free- 

 martins (females co-tvsdn with a bull) to sterile 

 ones is 3:1; and the ratio would not be very 

 different on any basis of division of the hetero- 

 sexual class that would help out the sex ratio. 

 Hitherto there have been no data from which 

 the ratio of normal to sterile free-martins 

 could be computed, and Cole futrnishes none. 

 I have records of 21 cases statistically homo- 

 geneous, 3 of which are normal and 18 ab- 

 normal. That is, the ratio of normal to sterile 

 free-martins is 1 : 6 instead of 3:1. 



This ratio is not more adverse to the normals 

 than might be anticipated, for breeders' asso- 

 ciations will not register free-martins until 

 they are proved capable of breeding, and some 

 breeders hardly believe in the existence of 

 fertile free-martins, so rare are they. 



My own records of 41 cases of bovine twins 

 (to date, February 25, 1916), all examined in 

 uterOj and their classification determined 

 anatomically without the possibility of error. 



