A MONOGRAPH OF THE 1?ATS OF NORTH AMERICA. 73 



ones, two other kinds are recognized as present in the American species 

 of VcspertiUo. The first of tliese is ontogenetic and consists in adnlts 

 not infr('(iuently retaining in an irregular manner some of the ])ro])or- 

 tions of the yoang. This I propose calling pedomorphic variation, or 

 ju'domorphism. The second is (Inc to depositions of black ])igment in 

 increased proportion in those parts of the skin which is not covered by 

 fnr, as on the ears, membranes, snout, and feet. This 1 propose calling 

 melanic variation. Pedomorphic and melanic variation is seen in all 

 three species. 



1 j)ropose presenting each of these subjects in some detail under dis- 

 tinct headings, as follows: 



Pedomorphic f(triation. — In young bats the foot and thumb are apt 

 to be dis[>roportionately large as compared with the same i)arfcs in 

 mature individuals; at the same time the auricle and tragus are corre- 

 si)ondingly siiuill, the snout high, blunt, and nearly naked. This dispo- 

 sition for our species occasionally to retain juvenile jteculiarities has 

 led to much confusion in their identitication. Prof. E. D. Cope has 

 proposed to employ for this condition the term retardation, that is to 

 say, the i)arts abo^'e named are, as it were, held back while others are 

 permitted to go on to adnlt expression. V. Incifuyus of Leconte is a 

 pedomorphic variety of V. f/ryphus as 1". yumanensis is a similar variety 

 of V. niti(h(ii. 



It is easily understood how necessary it is to determine the age of a 

 given specimen to be identified, since an immature form of the typical 

 example of a species may be similar to the fully grown adult from the 

 retardation of development in the characters above named. In quite 

 young individuals the fourth and tifth digits are of the same length 

 while the basi-occipital bone is not coossitied with the sphenoid, and 

 the epiphysis at the distal eiul of the metacarpal bone, as well as both 

 ends of the humerus, are detachable. In older speciniens, yet imnm- 

 ture, the proportions of the mauus are as in the adult while the joint 

 last named is still without sharpness of outline, thus indicating imper- 

 fection in development. The interfemoral membrane is triangular, the 

 tip of the tail boldly exserted, and the post calcaral lobe is absent. 

 The teeth are fully erupted long before the tail and the maniis are com- 

 plete, so that the characters presented by them are of little value in 

 determining age after the animals become independent food-seekers. 

 The study of the young, therefore, is of importance in the identification 

 of species. Mr. J. A. Allen (Mammals of Massachusetts) has stated 

 tliat in his judgment V. lucifuf/iis is the young of V. subuhttus, a state- 

 numt which is equivalent to saying that bats having the characteristics 

 above developed are always immature. I have, therefore, taken i)ains 

 to examine carefully the composition of the bones in the forms which 

 I have included in th«i moiu)graph under V. Iu<'ifi((/i<.s, and I can defi- 

 nitely assert that they are not immature. With the exception of the 

 characteristic retention in the head, foot, thumb, and interfemoral mem- 



