December 7, 1888.] 



SCIENCE. 



279 



■dertakes this work must remember, that, while all had much in 

 ■common, these nations had an independent character, and that 

 their laws, clans, feasts, traditions, and language varied greatly. 

 Morgan's valuable ■ League of the Iroquois ' was a good account 

 of the modern Senecas. Any one would be misled in applying it 

 strictly to the Onondagas. Each nation, therefore, is worthy of 

 independent study. If some competent person, conveniently near, 

 would undertake this for each reservation, the results would be of 

 great value. VV. M. Beauchamp. 



Baldwinsville, N.Y., Nov. i2. 



Species and Subspecies : A Reply to Mr. Conn. 



In Scu'iu-c- of May 25, 1888 (pp. 253, 254), Mr. H. W. Conn 

 reiterates a belief, held in common by Romanes and himself, that 

 there is a fundamental difference between what he calls ' varie- 

 ties ' and ' species.' The term ' variety ' is objectionable on the 

 •ground that it is susceptible of several meanings, and consequently 

 may be understood differently by different persons. It may be 

 assumed that the word is used by Mr. Conn in the sense in which 

 naturalists employ the term 'subspecies,' or 'geographical race.' 



Mr. Conn says, " There is no question in biology more signifi- 

 cant, or more difficult to answer, than what constitutes a species. 

 Upon the answer hinges the question of evolution, and more par- 

 ticularly the theories of Darwin. In spite of an immense amount 

 •of discussion, no answer has ever been given to the question which 

 is in any degree satisfactory." 



The above statement demonstrates the ignorance of its author 

 in matters well understood by those who handle species, and may 

 be taken as an illustration of the results of the methods of teaching 

 biology now employed in our leading schools, where systematic 

 biology is entirely lost sight of in the effort to impress upon the 

 student the superior importance of morphology, histology, and 

 •embryology : in other words, the student is encouraged to turn his 

 back to the broad field of nature, and to open his eyes only to peer 

 into the contracted field of the microscope. 



Systematic naturalists — those who have to do with the interre- 

 lations of existing forms of life — do not experience the difficulty 

 mentioned by Mr. Conn in defining " what constitutes a species," 

 and are forced to protest against his statement that " no answer 

 has ever been given to the question which is in any degree satis- 

 factory." 



A species is a group of individuals which resemble one another 

 in all essential respects, varying only within certain definable limits, 

 and which is separated from all similar groups by a well-marked 

 hiatus. A subspecies or geographical race differs from a species 

 in one respect only; namely, that intergrades exist connecting it 

 with the parent stock : in other words, a subspecies is nothing 

 more nor less than an incipient species. 



Mr. Conn holds that ' varieties ' are the result of variations in 

 structure outside of the reproductive organs, while ' species ' re- 

 sult from changes in the reproductive organs themselves. He says, 

 ■" \'ariety and species are therefore independent, being founded on 

 <lifferent kinds of variation." This hypothesis, it seems to me, is in 

 its very inception a contradiction of the genius of evolution. 



All forms of life inherit two tendencies, — one to reproduce ex- 

 actly the characteristics of their ancestors, the other to vary there- 

 from. Variation is the result of one or the other of two sets of 

 causes : namely, ( l) the influence of climatic or other physio- 

 graphic conditions ; (2) the accidental or sporadic acquirement of 

 a character which benefits its possessor, and hence is likely to be 

 perpetuated, and increased from generation to generation. In order 

 to clearly understand the laws of evolution, it is necessary to dis- 

 criminate between these two kinds of variation. In variation re- 

 sulting from the spontaneous acquirement of a beneficial character, 

 the line of evolution is geographically stationary, but is ascending 

 in time. Natural selection is the cause of this form of evolution ; 

 for the excess of individuals resulting from normal reproduction 

 brings about a struggle for existence, and the law of "the survival 

 of the fittest " results in the extermination of the parent form and 

 the successive intermediate stages, so that the modified form and 

 its ancestors are not in existence at any one period of time : in 

 other words, the line of descent niust be looked for in the history 

 of the past, among strata containing paleontologic remains. On 



the other hand, evolution due to geographic position — environ- 

 mental evolution — may present all intermediate stages at the same 

 time; the extremes, which we call subspecies, being found at dis- 

 tances remote from the centre of distribution of the type. Hence 

 in the study of evolution it must be constantly borne in mind that 

 there is this essential difference between ' geographic variation ' and 

 ' variation by natural selection : ' that in the one case intergrades 

 exist, in the other case they have become extinct during the pro- 

 cess of differentiation. 



Variation often takes place in more than one direction, produ- 

 cing several lines of differentiation which radiate from a common 

 centre. In such cases there will be several peripheral forms which 

 may differ from one another more markedly than each differs from 

 the parent or central type. 



In environmental variation the intermediate forms which connect 

 the extremes with the central type, or with one another, are termed 

 ' intergrades,' the peripheral forms being recognized as subspecies. 

 The term 'peripheral' is here used in a geographical sense, im- 

 plying that the individuals showing the peculiarity are found at 

 points remote from the centre of distribution of the type. 



It often happens that subspecies differ from one another and 

 from the parent stock as greatly as species themselves. It some- 

 times happens, also, that in the course of time the forms inhabiting 

 the intermediate region cease to exist, in which case the peripheral 

 forms previously known as subspecies become species at once, 

 without waiting for any further change ; the only difference be- 

 tween species and subspecies being, as already stated, that in one 

 case the intergrades exist, in the other they have become extinct. 



C. Hart Merriam. 



Washington, D.C., Dec. i. 



Rosenbusch's Petrography. 



Your reviewer, in his recent notice in your columns of Mr. 

 Iddings's admirable translation and abridgment of the first volume 

 of Rosenbusch's ' Mikroskopische Physiographie,' seems to me to 

 have hardly apprehended the exact aim of this work. Inasmuch as 

 the review, while not altogether unfair in its statements, may by its 

 general tone convey the impression to those unacquainted with 

 petrography that they are losing in the translation many essential 

 features of the original manual, I beg leave to give the results of 

 my own experience in the practical use of both books for purposes 

 of instruction in a petrographical laboratory. 



Heretofore the only available manual for the use of beginners in 

 petrography has been Rosenbusch in the original ; and every 

 teacher, even in Germany, must have felt that for this purpose the 

 book is somewhat cumbersome. My own experience has been that 

 the mass of detail, however advantageous and necessary to the 

 advanced worker, caused a loss of interest to students who were 

 beginning the subject, even when they belonged to a superior class 

 and possessed a tolerable knowledge of German. Those who, 

 from an intimate acquaintance with Professor Rosenbusch's trea- 

 tise, realized its great value, were loath to recommend even to be- 

 ginners any other guide ; and yet the need has long been fell of a 

 translation which should present all the essential features of the 

 work in English, without the mass of detail unnecessary for those 

 taking their first steps in petrography. This need the translator 

 has set before himself to fill, and in my opinion he has accomplished 

 the task in a most judicious and satisfactory manner. Since the 

 appearance of his translation a few weeks since, I have used it in 

 my laboratory with a success which I had begun to despair of ever 

 attaining with the original. Nothing really essential has been 

 omitted, while the book has been reduced to nearly half its former 

 size. The colored plate could be of no practical use to beginners, 

 but would have increased the price of the work verj' considerably. 



In his own preface the translator slates that he has had no ex- 

 pectation or desire to supplant the use of the original. No student 

 would dare to venture upon original investigation in petrography 

 without a knowledge of German sufficient to enable him to read 

 with ease the work in its extended form. To advanced workers 

 Rosenbusch will be now, as ever, a vast treasure-house of informa- 

 tion, which no abridgment of the translation will in any way cur- 

 tail. George H. Williams. 



Baltimore, Nov. 30. 



