1 62 WALTER LOUIS HAHN. 



not been able to find them at all during the period of gestation 

 and the rearing of the young, nor have I ever found the young 

 bats of either species o{ Myotis before they had reached adult size, 

 Pipistrelhis likewise leaves the cave for the breeding season, 

 although I have taken a female of this species containing three 

 small (about 2 mm.) embryos in the Twin Cave on June 6. 



The males of certain oriental species of bats (Chironieles tor- 

 quatns and some of the species of Cynopterus) have special adap- 

 tations for carrying the young. The Standard Natural History 

 (p. i6i) generalizes from this fact so far as to say that "it is not 

 doubtful that the male attends to his mate and young with con- 

 siderable assiduity." The absurdity of this statement in so far 

 as it applies to our common Vespertilionidae, is apparent from 

 the further statement on the same page that " the sexes do not 

 mingle and come together only at the nuptial season." There 

 is almost certainly no permanent mating but the animals copu- 

 late indiscriminately, several males perhaps mating with one 

 female. This is what might be expected in gregarious animals 

 that do not rear their young in a nest or den, but give birth to 

 them at any convenient place and carry them about. Rollinat 

 and Trouessart ('96) believe that this is what happens in the case 

 of Pipistreiliis pipistrelhis and Vespcrtilio vmrimis. 



The females of our species of Myotis, and perhaps the other 

 Vespertilionidse of eastern America, probably seek out isolated 

 places in which they give birth to the young and where they 

 spend most of the time while rearing them. As long as they 

 remain in the cave in the spring there is no complete segregation 

 of the sexes. I have found the two sexes associated in Twin 

 Cave on different dates in April (the latest examination was made 

 on April 25) both in the years 1907 and 1908. 



The females leave the caves somewhat earlier than the males. 

 On April 25, 1908, in a search through the outer parts of all 

 the caves on the Cave Farm, I found 23 male P. subflavtis 

 and 4 females. Twenty-five male M. Inciftigus were also found, 

 to only 2 females of that species. On May 13, in Truitt's Cave, 

 there were 17 P. subjlavits diwd 5 M. lucifngus, all of both species 

 being males. 



