G. GENERAL NATURAL HISTORY AND ZOOLOGY. 283 



for birds and reptiles from the Cretaceous to the present 

 time. Some additional conclusions in regard to American 

 tertiary mammals, as far as now known, are as follows: 1. 

 All the Ungulata from the eocene and miocene had upper 

 and lower incisors. 2. All eocene and miocene mammals 

 had separate scaphoid and lunar bones. 3. All mammals 

 from these formations had separate metapodial bones. At 

 the conclusion of the lecture, Professor Marsh announced 

 that his work in the field was essentially completed, and that 

 all the fossil remains collected and in part described were 

 now in the Yale CoUesie Museum. In future he should de- 

 vote himself to their study and full description, and he hoped 

 at no distant day to make public the complete results. JPo2)- 

 ular Science Monthhj^ November. 



MIMICRY IX BUTTERFLIES EXPLAINED BY NATURAL SELECTION. 



Fritz Miiller, in the Jena Zeitschrift^ endeavors to show how 

 the phenomena of mimicry in butterflies may be explained 

 by the theory of natural selection. He bases his inquiry 

 upon the species of Leptalis found in Southern Brazil, and 

 although, as will appear below, he adduces reasons for be- 

 lieving the primitive stock to have been banded, and not, 

 like most of the family to which the genus belongs, simple 

 white butterflies, he commences by showing how even such 

 an extreme change could be wrought out by the survival of 

 the fittest in the struggle for existence. " Should," he re- 

 marks, "the first unimportant variations from the original 

 white color (of the Pierids) be useful only in attracting to 

 their possessors, at a little shorter distance, the attention of 

 enemies flying constantly ovei'head, they would become more 

 and more useful, and cause their possessors to become con- 

 tinually more abundant in proportion to the type; they could 

 therefore serve as the basis for the gradual formation of a 

 resemblance fit to deceive even the sharp eyes of birds scan- 

 ning the swarms of Ithonias (the butterflies imitated by 

 some Leptalids) for booty." Further on he asserts that " the 

 acceptance, as the starting-point in the origin of mimicry by 

 natural selection, of a resemblance having its beginning at 

 such a distance can scarcely be shaken by a single known 

 case. It should, moreover, not escape attention that the 

 sharp-sightedness of enemies is itself also a quality at first 



