June, 1903.] 



KNOWLEDGE, 



125 



belonged to that animal. If that be the case, the ancient 

 cetaceans were mail-clad animals, and on that supposition 

 the bonv tubercles of the aforesaid porpoises must be the 

 remnants of such a coat of mail. A wonderful instance 

 of inheritance, if only it be true. 



Very isolated among living mammals are the anteaters, 

 sloths, and armadillos of Central and South America, 

 collectively constituting the typical representatives of 

 the order Edentata ; and until quite recently palaeontology 

 gave no clue as to their ancestry. All the living members 

 of the group are characterised by the absence of front 

 teeth (the anteaters, in correlation with the nature of 

 their food, being alone absolutely toothless) ; and their 

 cheek-teeth are of simple structure, alike in form, and 

 devoid of the hard enamel coating of less aberrant 

 mammals. The Tertiary deposits of Patagonia have, 

 indeed, yielded the remains of an armadillo furnished with 

 a full series of enamel-coated teeth ; but this, although a 

 step in the right direction, does not go far in affiliating 

 the group to other mammals. In the lower Tertiaries of 

 North America there have, however, been discovered the 

 remains of a group of extinct mammals — the so-called 

 ganodonts — which there is every reason to believe were the 

 ancestors of the modern edentates. These ganodonts have 

 in some instances a full series of differentiated and enamel- 

 clad teeth, and their skulls and limb- bones show a remark- 

 able resemblance to those extinct South American edentates 

 known as ground-sloths. Moreover, many of the later 

 forms display a tendency to a reduction in the number of 

 the front teeth, and to a partial or complete loss of the 

 enamel of those of the cheek series. On the other hand , 

 the earlier members of the group show evident signs of 

 affinity to the contemporary creodonts and ancestral 

 ungulates. In regard to their resemblances to the typical 

 edentates. Dr. VVortman* writes as follows: "If this 

 astonishing array of similarities is accidental, and does 

 not indicate genetic affinity, then all that can l)e said is 

 that paliEontological evidence is worthless in the deter- 

 mination of the various successive steps in the descent of 

 a group or species. I hold that, in view of all the evidence 

 above set forth, the preposition that the one has descended 

 from the other may now be regarded as a positively 

 demonstrated fact." 



As isolated at the present day as the edentates are the 

 rodents, or gnawing mammals, as exemplified by the rat, 

 the porcupine, the hare, i*cc. In all these animals the 

 single large pair of chisel-like incisor-teeth in the front of 

 each jaw grow throughout life, and thus never develop 

 roots ; while they are separated by a long gap (uuintei-- 

 riipted by a tusk, or canine) from the teeth of the cheek 

 scries, which never exceed lour pairs in each jaw, and -.iw. 

 all alike. A further peculiarity of the groiqi is the b;u'k- 

 ward and forward movement of the lower jaw (luring 

 naastication, as may be seen by watching a tame rabbit 

 feed. Till recently nothing definite has been known with 

 regard to the ancestry of the grouji ; but a short time ago 

 Pi-ol'cssor Osliorn poiiited out that mixodeetes and certain 

 other small mamiiialian types from tiie lower Eocene strata 

 of North America presented just such characters as might 

 naturally be looked for among ancestral rodents ; and he 

 proposed to regard them as forming a ]iriiiiitive section of 

 that group uiidi'r the name of Proglin's. Tiioy dillVr from 

 modern rodents l)y ].K)ssessiiig a full series of rooted incisor 

 and canine teeth, not sejiarated by a well-marked gap 

 from the cheek series, and the absence of a backwards and 

 forwards mot ion of the lower jaw. 



An ajiproxuiiation to the modern rodent type is, how- 

 ever, exhibited among certain members of this extinct 



• Bull. Amer. Muteum, Vol. IX., p. 104 (1897). 



group by the tendency to the enlargement of the second 

 jjair of incisors in each jaw (corresponding to the single 

 large pair of modern rodents), accompanied by the de- 

 generation of the other two pairs of those teeth and the 

 canines. And from these and other structural features 

 there seems considerable probability that the position 

 assigned to the group by Professor Oslwrn indicates their 

 real affinities. If so, the modern rodents are closely 

 connected with less aberrant mammals. 



Finally, we came to the Primates, which includes two 

 well-defined and sharply distinguished groups, one con- 

 taining man, apes, and monkeys, and the other the much 

 less highly organized ci'eatures commonly known as lemurs 

 or lemuroids. Widely sundered as are these two sub- 

 groups at the present day, there existed in Madagascar, 

 even so late as the human period, a creature which, 

 although evidently a lemur, exhilnts certain monkey- 

 characters. When, however, we descend to the basal strata 

 of the Tertiary period — the Lower Eocene— we meet, both 

 in Europe and North Amei-ica, with a number of small 

 mammals which are certainly referable to the Primates, but 

 exhibit characters tending on the one hand to connect that 

 group with other primitive mammals, and on the other 

 hand apparently to show an intimate relationship between 

 the ancestors of the modern anthropoids (man and 

 monkeys) and lemuroids. With regard to these early 

 foreruimers of the highest of all mammals. Professor 

 Osborn observes that three suppositions are possible : — 

 " First, that these Primates represent an ancient and 

 generalised group ancestral to botli Lemuroidea and 

 Anthropoidea ; second, that they include representatives of 

 both Lemuroidea and Anthropoidea, contemporaneous and 

 intermingled; third, that they belong exclusively to one or 

 the other order." Whichever of these suppositions be 

 nearest to the truth, it is evident that in Eocene times the 

 Primates were represented by a number of exceedingly 

 generalised forms presenting much the same relationshij^ 

 to the modern specialised monkeys and lemurs as the 

 primitive creodonts bear to modern carnivores and the 

 condylarthrous ungulates to existing hoofed mammals. 

 Further, these primitive Primates were themselves not far 

 removed from the ancestral caruivores and ungulates. 



In conclusion, as the result of the foregoing extremely 

 sketchy summary, it is quite clear that since the publica- 

 tion of the first edition of the " Origin of S])ecies " 

 palajontological investigations and discoveries have shown 

 that most of the main primary groiij)s of vertebrates i^m 

 the one hand and of the diflorent orders and families of 

 mammals on the other are respectively connected, as we 

 recede in time, by such a number of intermediate links an,i 

 gradations that "the gaps are now comparatively few and 

 far lietweeii. .\nd what is true with regard to mammals 

 is likewise true to a greater or lesser degree in the I'use of 

 reptiles and fishes. 



Gaps, and in some cases large ones, undoubtedly still 

 remain ; but in no single instance has any fact been 

 recorded with regard to the past history of vertebrates 

 which militates in the sliglitost degree against the theory 

 of evolution. On the contmry, everything points to a 

 continuous and orderly succession of forms of life 

 graduallv progressing from the primitive and generalised 

 to the modern and specialised types. 



The only rational explanation of such a regularly 

 progressive series — especially when the exist<?nce of 

 vestigial structures, like the splint-Kmes of the horse, in 

 certain forms is taken into consideration - that present.s 

 itself to the unprejudiced judgment is evolution, and we 

 venture to think that Dr. Wortman is fully justified in 

 his assertion that this may he regarded, from the palseon- 

 tological asjiect alom-, as a fully demonstrated fact. 



