58 



NATURE 



[November 15, 1900 



LETTERS TO THE EDITOR. 

 [The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he tindertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of NatuHe. 

 No notice is taken of anonymous communications.^ 



The Markings of Antilocapra. 



In Nature of Oct. ii (p. 586) Mr. R. J. Pocock says: "If 

 the American prong-buck were an inhabitant of Africa, I 

 presume that its conspicuous patterns . . . would be cited as 

 evidence supporting the theory of recognition marks. But in the 

 prairies of the United States there are no species that resemble 

 it in size and form, so as to create confusion as to identity." 



The prong-buck is so cited by Wallace (" Darwinism," p. 218), 

 and a figure is given (p. 219) of a similarly-marked gazelle in 

 support of the same theory. But the point of the whole matter 

 rests on the aid given to the members of a herd in following one 

 another, and has nothing whatever to do with the presence of 

 allied species. I cannot understand how Mr. Pocock, who 

 appears to have read Wallace's work, can have overlooked the 

 point of the argument so completely. I have had the pleasure 

 of seeing herds of prong-bucks (Antilocapra) in their native 

 wilds (Pecos Valley, and near the Sacramento Mountains, New 

 Mexico), and can readily understand how useful the markings 

 must be in helping the animals to keep together in the dusk or 

 <3ark, whereas it is not at all probable that they expect to escape 

 observation on the open prairie by daylight. If these animals 

 lived singly, there might be some plausibility in " Thayer's 

 principle," as applied to them, but in herds they can be seen 

 from afar off, and the same must be true of the African gazelles. 

 Their safety is in flight, not inconspicuousness, and the necessity 

 for keeping together when in flight is obvious. 



The coyote or prairie-wolf (C<3!«?> latrans and allies), which 

 also lives on the prairies and is gregarious, has the habit of 

 barking incessantly at night, and this doubtless serves the same 

 purpose as the markings of the prong-buck. 



It might conduce to clearness if we divided what are now 

 called recognition-marks into two categories, thus: — 



(i) Recognition-marks , which assist members of a species in 

 •distinguishing their fellows from other species. 



(2) Guide-marks, which assist members of a species in follow- 

 ing one another. The markings of the prong-buck would then 

 come under the head of guide-marks. T. D. A. Cockerell. 



East Las Vegas, New Mexico, U.S.A. October 30. 



Curves without Double Points. 



Mr. Basset's objection to the term "non-singular" (see 

 Nature, Oct. 11, p. 572), arises from a misunderstanding. 

 The ordinary use ot the term by English-speaking mathe- 

 maticians is natural and legitimate; it is appHed to curves 

 without double points when the curve in question is defined by a 

 relation among the coordinates of its points. In the case of a 

 curve defined in another manner, for instance by a tangential 

 equation, "non-singular" could not possibly be used in the 

 sense. In fact, the phrase which Mr. Basset denounces as 

 "exceedingly infelicitous and misleading" is one which, 

 Standing by itself as Mr. Basset quotes it, strikes a geometrician 

 as unfamiliar; " non- singular cubic curve," "non-singular 

 curve of the wth order," are familiar to him, and are un- 

 objectionable. 



In the study of algebraic curves the word n'^de is in common 

 use to denote any double point ; if it is necessary to distinguish 

 the three chief kinds of double points, the words crunode, 

 acnode, cusp are recognised ; and, although the two first are 

 not wholly satisfactory, yet their meaning is unmistakable. 

 Further, we have adjectives nodal, crunodal, cuspidal, binodal, 

 etc. If Mr. Basset's mode of investigation is such that the 

 introduction of new technical terms is really unavoidable, may I 

 suggest that the phrase nodeless curve concisely describes a curve 

 without double points ? Herbert Richmond. 



King's College, Cambridge, November 10. 



Euclid i. 32 Corr. 



Hamblin Smith writes, these " corollaries were first given 

 in Simson's edition of ' Euclid'" (edition 1872, &c.). J. Walms- 

 ley, "Introduction to Geometry" (1880, &c.), styles them 

 Simson's corollaries. Hall and Stevens say these " theorems 



NO. 1620, VOL. 63I 



were added as corollaries to Prop. 32 by Robert Simson " 

 (1888, &c. ), and finally, Loney, in his edition of Todhunter's 

 " Euclid," writes, " the corollaries were added by Simson." 

 Many years ago it was pointed out to me that these corollaries, 

 with many interesting applications, were given by Clavius in his 

 edition of the Elements (1607), see pp. 105-108. On p. 107, he 

 cites "ex Campano, si pentagoni singula latera producanlur 

 in partem utramque, ita ut quislibet duo extra pentagonum 

 coeant, efificientur quinque anguji ex lateribuscoeuntibussequales 

 duobus solum rectis. " Clavius probably is not the first pub- 

 lisher of these results. R. Tucker. 

 November 5. 



Late Appearance of a Humming-bird Moth. 



In a garden in Lower Addiscombe Road (well in the town of 

 Croydon), I saw a humming-bii:d hawk-moth to-day sporting 

 over a bed of scarlet geraniums. It was as fresh as if newly 

 emerged. This is the first time I have seen the insect so late in 

 the year. Would it not have been called a " late appearance" 

 even a month ago.? It testifies strongly to the unusually open 

 autumn here. J. Edmund Clark. 



Lile Garth, Ashburton Road, Croydon, November 3. 



SOME RECENT ADVANCES IN ZOOLOGY. 



TO take stock from time to time of the progress 

 made in its different branches is advantageous in 

 the case of every science, but in none more so than 

 in zoology, where specialisation is now carried to such 

 an extent that the workers in one section have in 

 general but little acquaintance with what their brethren 

 are doing in another. This same subdivision of work 

 renders it, however, extremely difficult for any single 

 writer to give any adequate account of what has been 

 effected during the last year or two in all the different 

 branches of the science, the difficulty being enhanced 

 by the circumstance that the one for 1898 is the latest 

 volume of the " Zoological Record " that has at present 

 been published. All that can therefore be attempted in 

 the present article is to give a fairly full resume of the 

 more notable advances in the branches of zoology with 

 which the writer is best acquainted, and to make men- 

 tion of such discoveries in other sections of the subject 

 as may have come under his notice. 



Among the Mammalia, by far the most important dis- 

 covery made of late years is the identification by Mr. J. P. 

 Hill, of Sydney, of the existence of a rudimentary placenta 

 in the Bandicoots (Perameles). From this it has been in- 

 ferred that all Marsupials originally developed a placenta, 

 which has become abortive in the more specialised mem- 

 bers of thegroup. Thisdiscoveryentails,almostofnecessity, 

 a modification in the generally accepted classification of 

 the Mammalia. And instead of dividing the class into 

 the three equivalent groups, Eutheria, Metatheria and 

 Prototheria, Prof. H. F. Osborn has suggested that we 

 should now take only the two divisions of Eutheria and 

 Prototheria ; the former being subdivided into Placentals 

 and Marsupials, and the latter (as heretofore) including 

 the Monotremes alone. Placentals and Marsupials may 

 indeed be now regarded as divergent branches of a single 

 stem ; the latter being less primitive than are the Insec- 

 tivora. On the other hand, Monotremes are so different 

 from Eutherians that some zoologists even go so far as to 

 consider them derived independently from Reptiles or 

 Amphibians. In this connection, as tending to emphasise 

 the intimate relationship between Marsupials and the 

 primitive Carnivora, reference may be made to a paper 

 by the present writer {P.Z.S., 1899), in which it is 

 attempted to show that both have a similar dental 

 formula. It may be added that our knowledge of the 

 anatomy of the Monotremes has been largely increased 

 by the publication of the results of the work on the speci- 

 mens collected by Dr. Semon, now in course of publication 

 in the Jenaische Zeitschrift. Moreover, much interest 



