deciduous teeth there is clearer evidence of more specialization for a diet of flesh in the deciduous teeth than in the permanent teeth. For example, the upper carnassial of the milk dentition is even more highly sectorial than is the permanent tooth and strikingly like that of some of the cats. The lower tooth that is effective in the shearing action bears no more trace of the metaconid than does the permanent first lower molar. These features of the deciduous dentition suggest that it is more specialized for a diet of flesh than is the permanent dentition. If this be the fact, it may seem especially remarkable because the commonly employed term "milk teeth" suggests that the animal makes but little or no use of these teeth in the short time that they are in place. Accordingly, the student may credit the form of these teeth more to some indirect effects of inheritance than to natural selection acting directly upon the teeth. But, after all, natural selection probably is responsible for the form of these teeth as is indicated by the observations of Hamilton (1933:318-325). He found that these milk teeth are used for eating solid food as soon as the principal shearing teeth are in place. This is three weeks after birth and before all of the deciduous teeth have broken through the gums. These shearing teeth are used for almost two months before being replaced by the permanent teeth and it is, therefore, evident that natural selection could operate to fully as great a degree in determining the form of the deciduous teeth as it may with the permanent teeth.

Hamilton (1933:325-326) found that the permanent dentition was complete at 75 days after birth in captive specimens of Mustela frenata noveboracensis. In the same subspecies, he noted 28 days after birth that the canines and carnassial teeth [second deciduous cheek tooth above and third below] had erupted through the gums. Animals 45 days old, Hamilton found, were losing the milk dentition, and had the gums broken through by several of the permanent cheek teeth.

Study of the cleaned skulls available of juveniles indicates that the deciduous teeth which persist longest are, on each side of the mouth, the second cheek tooth above and the third cheek tooth below. These teeth persist until after the permanent P4 and m1 have come into use. These permanent teeth are situated immediately behind their functional counterparts of the milk dentition. P3 and p4 are the teeth of the permanent dentition which ultimately push out the last milk teeth to be lost. Accordingly, in the permanent dentition, P4 and M1 appear before P3 does, and m1 and m2 make their appearance before p4.

DISPARITY IN NUMBERS OF MALES AND FEMALES (IN ZOOLOGICAL COLLECTIONS)

The question has frequently been asked why twice as many male as female weasels are captured. This is the proportion in research collections, as may be seen from table no. 2, and I am convinced that the specimens in these collections are saved in approximately the same proportion as that in which they are caught. Although it might be assumed, upon first consideration, that there are twice as many males as females in nature, selective factors enter into the catch. For example, because a male weasel is approximately twice as heavy as a female, it may be necessary for him, in a given length of time, to travel twice as far as the female to obtain the required amount of food with the result that a given number of traps or snares will catch twice as many males as females. Indeed, Glover (1943B:8) shows that, on the average, in Mustela frenata noveboracensis in Pennsylvania, the male actually does travel slightly more than twice as far as the female (704 feet versus 346 feet). From table no. 2, it may be seen that in most winter months the ratio is 3 males to one female. This ratio is reasonable enough, in view of what has been said, if it is considered also that the lighter weight of the female permits her safely to step on the pans of traps that would be sprung by heavier males.

If in the breeding season, which is April through August in M. frenata, the female is passive and if the male is restlessly searching for her, he may thus increase still more his chances of being caught in traps set for weasels.

My own studies of live weasels in nature indicate that in the season when females are attending young which are half grown, or larger, the adult male weasels live singly in dens of their own, separate and apart from the females and their young (Hamilton, 1933:328, records adult males living with the female and her young, but possibly this was when the young were less than half grown). Perhaps these males at that time travel no farther than is necessary to obtain food for themselves. Females, at this time, forage not only to meet their own needs, but for food to supply their young as well. At this time, in May and June, as may be seen from table no. 2, almost as many adult females as adult males are caught. The reason why only relatively more females than in other months, instead of actually more females than males, are caught at this time probably is that the adult males also are extraordinarily active at this time because they are in breeding condition. Perhaps the explanation in part is to be found in the lesser weight of the female (approximately half of the male's weight) which, as indicated above, permits her to step on the pan of a steel trap without springing it whereas the heavier male does spring the trap and as a consequence is caught. Hamilton (1933:299-300), who mentions this selective factor, found an equal number of males and females in the three newly born litters that came under his observation.

Table 2
Specimens of Mustela frenata (north of the range of M. f. frenata) arranged by sex and under each sex by age