834 



SGIENGE. 



[N. S. Vol. VII. No. 181. 



A PRECISE CEITEEION OF SPECIES. 



To THE Editor op Science : Your note in 

 Science No. 178 on the recent paper by Dr. 

 Davenport and Mr. Blankinship on a ' Precise 

 Criterion of Species ' raises a question whicli I 

 thinli you do not follow to its necessary con- 

 clusion. That the criterion of species is a prob- 

 lem largely made up of psychological elements 

 seems an almost self-evident proposition, and 

 as I understand the paper in question its object 

 is simply to tabulate these psychological ele- 

 ments and draw from them an exact statement 

 of accepted current usage. From this tabula- 

 tion it appears that in America, during the 

 present decade, groups of animals whose differ- 

 ences may be expressed by one kind of curve 

 are currently regarded as species, while those 

 whose differences give another curve are looked 

 upon as subspecies. But why should the ques- 

 tion be left here? If the curves were made 

 from data furnished by determinations current 

 in America during the past decade or in Europe 

 now they would be strikingly different from 

 those actually obtained by Dr. Davenport. An 

 almost equally noticeable discrepancy would 

 occur between the curves furnished by the work 

 of certain American and European systematists 

 at the present day as compared with those of 

 some of their respective compatriots.* Further- 

 more every individual worker passes through 

 phases of opinion in each of which his work 

 would give appreciably different curves. It 

 appears to me, therefore, that Dr. Davenport 

 and Mr. Blankinship have elaborated not so 

 much a precise method of distinguishing be- 

 tween species and sub-species as for graphically 

 representing the opinions of different times and 

 individuals. In other words, they have shown 

 how to make a Linnfeus-curve, a Brehm-curve, 

 an America-curve or an 1898-curve — which 

 when compared together have an undoubted 

 psychological interest — but they have not fur- 

 nished a criterion which will be of actual service 

 to working systematic zoologists. The reason 

 for this failure is partly, as Dr. Davenport sug- 

 gests in his letter in Science No. 179, due to 

 the complexity of the method, but more espe- 

 cially to the fact that systematists, from the 

 * I write from the standpoint of mammalogy and 

 ornithology. 



very nature of their work, must hold themselves 

 ever ready to accept new points of view and 

 new standards of value. 



Geerit S. Millee, Je. 

 U. S. National Museum. 



SCIENTIFia LITERATURE. 

 A Text-book of Entomology, including the Anatomy, 

 Physiology, Embryology and Metamorphoses of 

 Insects, for use in Agricultural and Technical 

 Schools and Colleges, as well as by the work- 

 ing Entomologist. A. S. Packaed. Macmil- 

 lan Company. 1898. 8vo. Pp. 729. 654 figs. 

 Students of entomology who began their 

 work some fifteen or twenty years ago often 

 found Professor Packard's ' Guide to the Study 

 of Insects' the only accessible American book of 

 reference on the subject of general entomology. 

 It was a large volume, containing much valu- 

 able material, but it never seemed to satisfy one 

 even on minor questions. It contained anat- 

 omy, physiology, embryology and taxonomy in 

 a somewhat undifferentiated condition. The 

 redeeming feature of the work was the wide 

 philosophical interest that its pages inspired. 

 This interest had its source in Professor Pack- 

 ard's own industrious and enthusiastic study of 

 the subject of entomology, a study which he 

 has extended without interruption during the 

 thirty years that have elapsed since the publi- 

 cation of the ' Guide. ' The results of this long 

 study now lie before us in this able text-book. 

 The recent publication of Comstock's ' Man- 

 ual' and Sharp's volume on insects in the 'Cam- 

 bridge Natural History' has evidently led Pro- 

 fessor Packard to exclude a consideration of 

 the taxonomy of insects and to confine his 

 treatment to the morphological and physiolog- 

 ical aspects of the subject — a task surely very 

 great even as thus limited. He takes up in 

 succession the anatomy, embryology and meta- 

 morphoses of insects, giving more or less atten- 

 tion to the physiological aspect as he proceeds. 

 His presentation of this last aspect is, perhaps, 

 the weakest portion of the book, because Pro- 

 fessor Packard has not made special up-to-date 

 studies in this field. He omits all mention of 

 several interesting physiological facts, such as 

 Professor J. Loeb's interesting experiments on 

 the heliotropism and stereotropism of insects. 



