April 2, 1894.] 



KNOWLEDGE. 



73 



AN ILLUSTRATED 



MAGAZINE OF SCIENCE 



SIMPLY WORDED— EXACTLY DESCRIBED 



LONDON: A PHIL ■?, 1894. 



CONTENTS. 



Ground-Sloths. By R. Ltdekkee, B.A.Cantab 



The Making of Diamonds. By VAnenAN Coenish, M.Sc, 



F.C.S 



Stinging Insects. — III. By E. A. Butler 



The Great Sanitary Lesson of the Crimean War. 



By G. B. LoxGSTAFF, il.A., il.D.Oxou., F.R.C.P., &c. ... 

 The Thermal Radiation from Sunspots. By W. E. 



Wilson, M.R.I.A 



The North Pole of the Moon. By A. C. Rantabd 

 Science Notes 



Notices of Books 



Letters:— .J. Muneo : Chaeles MacItee; E. L. Gabbett 

 Weighing the Earth. By J. J. Ste-svaet, B A., B.Sc. 

 The Phcenicians, or Palm-Tree People. By J. H. 



illTCHIXEK, F.RA.S. 



The Root-Tubercles of Peas and Beans. — Part 11.^ 

 By J. Pextlaxd Smith, M.A., B.Sc 



The Face of the Sky for April. Bt Heebert Sadler, 

 FR.A.S. ; 



Chess Column. By C. D. Locock, B.A.Oxon 



PAGE 



7.3 

 76 



80 



82 

 83 

 8.5 

 86 

 86 

 88 



89 



91 



94 

 95 



GROUND-SLOTHS. 



By E. Lydekker, B.A.Cantab. 



SUFFICIENTLY protected from all attacks on the 

 part of the wolf-like marsupials, and such other 

 large carnivorous mammals as may at the same 

 period have roamed over Argentina, the pigmy 

 glyptodont of the Santa Cruz beds of Patagonia 

 could have had difficulty iu maintaining its existence 

 against foes of all kinds, and subsequently giving rise to the 

 gigantic mailed monsters which we endeavoured to describe 

 in our last article. Side by side with this well-defended 

 creature there lived, however, another not less remarkable 

 mammal, of nearly similar dimensions, and likewise 

 belonging to the great order of edentates, then, as now, so 

 characteristic of South America. This creature had, how- 

 ever, no such coat-of-mail as that which defended its 

 contemporary (though there is a possibility that some bony 

 granules may have been imbedded in its undefended skin), 

 and as it appears to have been equally devoid of weapons 

 of offence, while it did not derive protection from an 

 arboreal life, it may be a matter of wonder how it managed 

 to fight its way through the struggle for existence. That 

 it did so is, however, perfectly clear, since the pigmy 

 ground-sloth, as the animal in question may be called, is 

 clearly the ancestral type from which were subsequently 

 evolved those gigantic edentates of the Pleistocene deposits 

 of the Argentine scientifically known by the names of 



Megatherium, Mylodont, etc., but which may be collectively 

 designated ground-sloths. These, although unprotected 

 by any means of defence, being among the most gigantic 

 of mammals had, it is needless to say, no diificulty in 

 holding their own ; and it is only with regard to their 

 pigmy ancestors that we have any cause for wondering 

 how they managed to survive. Possibly, however, these 

 pigmy gi-ound-sloths were burrowing creatures, like the 

 great anteater of the present day, and lived in holes 

 excavated by their powerful claws ; and if this should be 

 the case, the difficulty as to their survival vanishes. 



Sloths are, however, such essentially arboreal creatures, 

 as characteristic of the Brazilian forests as are squirrels 

 and dormice of our own woods, that our readers will want 

 to know what we mean by using such an apparently con- 

 tradictory term as ground-sloths. 



To justify ourselves, and at the same time to enable our 

 readers properly to understand the structure of these 

 strange extinct edentates, we must enter into a short 

 dissertation on the subject of sloths, and likewise of their 

 distant cousins the anteaters. 



The external form and long shaggy hair of the sloths are 

 too well Imown to require description, and we accordingly 

 pass on to draw attention to certain peculiarities in regard 

 to their skeletons and teeth which will aid in explaining 

 the reason for the term ground-sloths. In the first place, 

 then, sloths (which, as all our readers are doubtless aware, 

 are comparatively small animals) are characterized by 

 their peculiarly short and roimded heads, which have an 

 almost spherical form. If we examine the skull of one of 

 these animals, we shall find, as in those of other members 

 of the same order, a total absence of front teeth ; while 

 the cheek-teeth comprise five pairs in the upper, and four 

 in the lower jaw. 



Those who recall our article on " Armadillos and Aard- 

 Varks," published in an earlier number of this journal, 

 will not fail to recollect that in all edentates the teeth are 

 devoid of the hard enamel so characteristic of those of 

 other mammals. In the sloths we find that the teeth form 

 short cylinders, of which the outer layer is harder than 

 the central core, in consequence of which their grinding 

 surfaces become slightly cup-shaped. In the three-toed 

 sloths ( Bradypus) the whole of the teeth are of this 

 extremely simple type ; but in their two-toed cousins 

 [Chohepits) the first pair in each are longer than either of 

 the others, and are modified into a somewhat tusk -like 

 form, the upper ones wearing against the front of the 

 lower ones so as to produce by mutual attrition an oblique 

 bevelled sm-face at the top of each. The limbs of the 

 sloths are remarkable for their length and slenderness, 

 but the front pair are much longer than the hinder ones. 

 The narrow and cui-ved feet terminate in long hooked 

 claws, which in the three-toed species are three in number 

 in each foot, although in the fore feet of the two-toed 

 sloth they are reduced to a pair ; in fact, the feet are 

 reduced to the condition of little more than hooks, 

 admirably adapted for suspending the animal back-down- 

 wards from the boughs of trees, but forming poor 

 instruments for terrestrial progression, sloths when on the 

 ground walking slowly and awkwardly, with the soles of 

 the feet turned inwards, and the weight of the body 

 supported on their outward edges. It is important to 

 notice that in the skeleton of the feet the terminal bones, 

 or those ensheathed in the long claws, are not longitudinally 

 grooved on the upper surface. 



The South American, or true anteaters, one of which 

 is terrestrial, while the other two are more or less arboreal 

 in their habits, are so unlike the sloths that it is difficult 

 to believe they have any near relationship with the latter ; 



