772 



SCIENCE 



[N. S. Vol. XXVIII. No. 726 



thus permitting the work of natural selection 

 in increasing the numbers to work without 

 interruption. 



The recessive character, on the other hand, 

 only occasionally manifests itself, so that 

 natural selection seldom has an opportunity to 

 aid it. This advantage that dominance wins 

 for the characteristic is especially important, 

 because the early generations are the ci-itical 

 period for every new characteristic. Even a 

 favored characteristic may succumb during 

 the early days, when all the eggs are in one 

 basket, so to speak, so numerous are the chance 

 deaths. 



Trimorphic heredity, where the heterozy- 

 gotes constitute a third form different from 

 the parents, also affects the action of natural 

 selection. In this ease the utility of the new 

 characteristic is less important than the utility 

 of the heterozygous characteristic in the 

 determination of the fate of the characteristic 

 in question. In some eases, the heterozygous 

 characteristic is so different, as in the An- 

 dalusian fowl, that it is quite conceivable that 

 the selective value of the heterozygous char- 

 acteristic might be even opposed to that of the 

 original characteristic. More frequently it 

 would have a decreased value, whether it be 

 negative or positive, which may reduce it to 

 no selective value. A characteristic might 

 have a high utility, but if its heterozygotous 

 condition lacked it, it would probably fail un- 

 less some other factor, such as assortative 

 mating or determinate evolution, should come 

 to its rescue. There is a possibility that the 

 heterozygote might be favored by a selective 

 value with the extracted characteristic 

 neutral. It might then be successfully estab- 

 lished by natural selection in spite of its own 

 lack of selective value. Again the hetero- 

 zygous characteristic may be favored and the 

 extracted characteristic opposed. In that case 

 the success of the heterozygote would be 

 jeopardized. Rescue might come for it in the 

 shape of a fixed heterozygous condition, such 

 as that of the Barred Rock poultry. 



The method of inheritance plays, then, a 

 large role in the action of natural selection, 



EoswELL H. Johnson 

 October 11, 1908 



THE OTTEK IN MASSACHUSETTS 



It is not commonly knovm that the North 

 American otter (Lutra canadensis) is nowa- 

 days anywhere in Massachusetts a frequent 

 victim of the trap or the gun of the hunter. 

 It appears, however, that the otter has escaped 

 extermination in spite of its valuable fur, and 

 in certain sections of the state has apparently 

 gained in numbers. The solitary habits of 

 the animal and its shyness may have conduced 

 to its preservation. It has, nevertheless, al- 

 ways been eagerly sought wherever its presence 

 has become known, on account of the beautiful 

 pelt, which to-day has a substantial market 

 value. 



The persecution of these valuable fur-bear- 

 ing mammals, it would seem, would have led 

 to their extinction. While their shyness and 

 general recluse habits are in their favor, their 

 size and certain other instinctive habits are 

 against them. The otter seems to be a playful 

 creature and apparently enjoys a frolic with 

 a companion or alone. During the rutting 

 season, perhaps at other times as well, it is 

 known to enter into the pastime of sliding on 

 the snow or a muddy river bank into the water 

 of a stream or pond, and to repeat this per- 

 formance many times. These otter slides are 

 the trappers' " signs." Apparently, too, the 

 creature may have a sort of " playground " 

 or place where it more or less regularly leaves 

 the water for a roll in the snow or mud. 



The great traveling capability of the otter 

 is attested by its wide distribution. It is said 

 to be generally distributed over North Amer- 

 ica, apparently in no great abundance at any 

 one place, but likely to be met with in locali- 

 ties adapted to its habits. The roaming habit, 

 of course, in a way stands between it and 

 destruction. In its new haunts it may live 

 and breed for some time, undiscovered. In 

 the old it would probably have been hunted so 

 relentlessly that it would have been extirpated. 



It is to me a matter to occasion some sur- 

 prise that the otter is as abundant as records 

 seem to show, in certain parts of this state. 

 The otter has always been included in a list 

 of the mammalian fauna of the state. It 

 appears at no time to have become so deci- 



