DECESfBER 1, 1892.] 



KNOWLEDGE. 



221 



^^ AN ILLUSTRATED "^^ 



MAGAZINE OF SCIENCE 



SIMPLY WORDED— EXACTLY DESCRIBED 



LONDON: DECEMBER 1, 1892. 



CONTENTS. 



Armadillos and Aard-Varks. ByK. Ltdeeicer, B.A.Cantab. 



On the Distribution of Stars in the Milky Way. By 

 Jonx Richard Scttox, B.A.Cantab 



Caterpillars— 11. By E. A. Butieb 



Photographs of Swifts Comet. Br Pi-of. E. E. B.^bxard 



On the Forms of Comets Tails. By A. 0. Rantard 



Science Notes. 



Recent Trade and the Nation s Drinking Habits. By 



Alex. B. .MArDowAi.T. MX. " 



Notices of Books 



Letters : — \V. F. Kirhv : \V. T. Lynx; W. H. S. Moxeic 



The Face of the Sky for December. By Hebbert 

 Sadler. F.R.A.S 



Chess Column. By C. D. LococK.B.A.Oxon 



PAGE 



221 



224 

 226 

 229 

 229 

 231 



232 

 234 

 23.T 



238 

 239 



ARMADILLOS AND AARD-VARKS. 



By R. Lydekker, B.A.Cantab. 



OF the three animals represented in the figures 

 accompanying the present article, two are suflS- 

 ciently alike to suggest to the ordinary observer 

 their relationship to one another, but the third 

 is so utterly ditiereut, that it is difficult to pomt 

 out any important character it has in common with the 

 two others ; nevertheless, naturahsts generally regard all 

 these three strange creatures as belonging to a single order 

 of mammals, for which the name of Edentata is adopted. 



Fig. 1.— The Threi'-Banded Armadillo. 



The signification of the term Edentata being toothless, the 

 unsophisticated student would naturally be led to suppose 

 that all the animals so named were utterly devoid of those 

 useful but troublesome appendages. This, however, is 

 far from being the case, the majority of the members of 

 the group (among which are those figured here) having a 

 considerable number of teeth. Still there is one feature 

 in connection with the dentition exhibited by the whole of 

 these so-called edentates ; and this is, that teeth in 

 the front of the jaws, corresponding to the incisors of 

 other mammals, are totally absent. Instead, therefore, of 

 being described as edentates, or toothless mammals, these 

 creatures ought rather to have been named aprotodonts, 

 or incisorless mammals. After all, however, it is not 

 much consequence what is the proper meaning of a name, 

 so long as we know the sense in which it is used, and 

 there is accordingly no real objection to the employment 

 of the tei-m edentates, which has obtained the almost 

 universal sanction of zoologists. 



In addition to this total absence of front teeth, the 

 edentates are further characterized by the circumstance 

 that all their teeth (when they possess any) show no trace 

 of the hard layer of enamel which is so characteristic and 

 essential a constituent of those of other mammals ; these 

 teeth at no period of life forming roots, but continually 

 gi'owing from below. Jloreover, in nearly all the eden- 

 j tates there is never any set of milk-teeth developed, 

 i although, uufortimately. this cannot be taken as a charac- 

 teristic of the order, since such teeth occur in one of the 

 armadillos, and also in the animal represented in our 

 thhd figure. 



Premising that the edentates are quite distinct from the 

 marsupials and egg-laying mammals, we may say, then, 

 that the only features by which they can be collectively 

 characterized are the want of front teeth, and the absence 

 of enamel on those of the cheek-series, while in certain 

 rare instances they may be utterly devoid of teeth. 

 Such characters, it must be confessed, are by no means 

 of first importance. 



The mammals thus associated by these negative charac- 

 teristics are now chiefly confined to the southern hemi- 

 sphere, and include the sloths, anteaters, and armadillos 

 of South America, the pangolins, or scaly anteaters of 

 South-eastern Asia and Africa, and the aard-varks of 

 Africa ; the true anteaters and pangolins being those in 

 which teeth are wanting. In past times they were also 

 represented by the gigantic megathere, and a number of 

 other allied extinct forms ranging throughout America, 

 which in some respects serve to connect the sloths with 

 the anteaters. This marked restriction of the existing 

 edentates to the southern hemisphere, and their especial 

 abundance in South America, at once stamps them as a 

 very lowly group of animals, there being a well-marked 

 tendency for the preservation of the humbler forms of life 

 in the southern continents and islands of the globe. There 

 is, indeed, a question whether the pangolins, and more 

 especially the aard-varks of the Old World, have any real 

 kinship with the more typical American edentates, but 

 apart from this possibility of the artificial nature of the 

 group as at present constituted there can be no doubt but 

 that all its members are what may be called degraded 

 types — that is to say, that instead of having advanced in 

 the struggle for existence they have lost some of the 

 a,ttributes of the higher animals ; evidence of this degrada- 

 tion being aftbrded by the indications above mentioned of 

 their having been formerly provided with two sets of teeth. 

 In saying that the edentates are lowly and degraded 

 examples of the mammalian ty^ie we by no means intend, 

 however, to imply that they are not admirably adapted to 



