June 1, 1893.] 



KNOWLEDGE 



103 



the piDininilux raiiKmix : and it is by the action of 

 this muscle on their lieads that the spines are raised from 

 a recumbent to a vertical position when tlie creature rolls 

 itself up into a ball — an action of which all porcupines are 

 quite incapable. Not only does the hedgehog differ from 

 the porcupine in this respect, but it is likewise peculiar in 

 using its spines as a means of protection when throwing 

 itself down a vertical bank or precipice, and by this means 

 is able to accomplish a vertical descent of over a dozen feet 

 without the slightest harm. As regards the develop- 

 ment of its spiny armour, the hedgehog is perhaps the 

 most highly specialized of all the spiny mammals in spite 

 of the inferior length of its spines as compared with those of 

 the porcupine. Hedgehogs are now represented by about 

 a score of species ranging over Europe, Africa, and a 

 considerable portion of Asia ; while the existing genus 

 dates from the middle portion of the miocene division of 

 the tertiary period. That the spines characterizing the 

 existing forms have been independently developed within 

 the limits of the group is pretty conclusively indicated by 

 the close affinity of the hedgehogs to the long-tailed and 

 spineless Malayan inseetivores known as gymnuras ; fossil 

 types apparently indicating an almost complete transition 

 from the gymnuras to the hedgehogs. In case anyone 

 should suggest that the latter, and not the former, might 

 be the ancestral stock, it may be mentioned that while the 

 gymnuras have a generalized type of dentition and long 

 tails, the hedgehogs have the teeth much reduced i 

 number and specialized in character, and short taDs. 



In Madagnscar the place of the hedgehogs is taken by an 

 entirely different group of inseetivores known as the 

 tenrecs, all of which have a certain number of spines 

 mingled with the fur, at least in the young condition, 

 and some of which are so hedgehog-like in general appear- 

 ance that by the non- zoological observer they would 

 certainly be regarded as members of the Krinaceida. The 

 tenrecs differ, however, from the hedgehogs precisely in tho 

 same manner as the golden moles were shown in our last 

 article to differ from the true moles — that is to say, 

 whereas in the latter the crowns of the upper molar teeth 

 are quadrangular, with their cusps arranged in a some- 

 what W-like manner, in the former these teeth are 

 triangular, with their cusps arranged in a V. There are 

 five species of tenrecs, classed under three generic headings, 

 and all characterized by the absence or small size of the 

 tail. The largest, and at the same time the most 

 generalized of all, is the common tenrec [Centetes ecuwlatus), 

 which attains a length of from twelve to sixteen inches, 

 and is characterized by the absence of a tail, by the rows 

 of spines on the back being shed in the adult state, and 

 also by certain peculiar features in the dentition which 

 appear to indicate relationship with the pouched mammals. 

 The spiny tenrecs (Hcmirentctcs) are much smaller animals, 

 of the size of moles, in which the longitudinal rows of 

 spines on the back are retained throughout life. They 

 have the same number of teeth as fully adult individuals 

 of the common tenrec ; but whereas in the latter there 

 are four upper molars and two upper incisors, in 

 the spiny tenrecs there are three of each of these teeth. 

 In the loss of the last molar these tenrecs are 

 e\'idently more specialized than the common species, but 

 the presence of the third incisor shows that they are 

 descended from a still more generalized type. Lastly, 

 we have the hedgehog-tenrecs {Kriculm), in which the 

 whole upper surface of the body, as well as the short 

 tail, is thickly beset with spines, thus giving the hedge- 

 hog-like appearance from which the creatures derive 

 their name. The dentition is more reduced than in 

 either of the upper groups, thus indicating the greater 



specialization of the genus ; although the presence of a 

 short tail indicates direct descent from a tailed ancestor. 

 Although it is quite clear that the three genera of tenrecs 

 are divergent branches from a common stock, yet it is not 

 impossible that they may indicate the manner in which 

 the complete coat of spines characterizing the third 

 group has been gradually evolved. Against this view it 

 may, however, be urged that if the common tenrec indi- 

 cated the first commencement of the spiny coat, it would 

 be more likely to find the spines in the adult rather than 

 in the young. Be this as it may, the wide difference 

 between the hedgehogs and the tenrecs, coupled with the 

 affinity of the former to the gymnuras, leaves no doubt 

 that the spines have been acquired independently in the 

 two groups. 



^#?si*ii^ 



FiO. 3. — The Common Spiny Anteater. 



As we found the last representative of the mole -like 

 animals among the pouched mammals, so we observe 

 that spiny animals are represented among the still lower 

 egg-laying mammals by the spiny anteaters, or echidnas, 

 of Australia and New Guinea. As most of the leading 

 peculiarities of the spiny anteaters have been already 

 described in a former article in Kno^-ledge, treating 

 of the egg-laying mammals, it will be unnecessary 

 to say much on this subject here. The two kinds of 

 echidnas differ, however, externally from all the spiny 

 animals hitherto mentioned in the production of the 

 muzzle into a long, edentulous, tubular beak ; and their 

 spines are short, and in some cases largely concealed by 

 the fur. Neither of them have the power of rolling the 

 body into a ball ; and, whereas the Australian echidna has 

 five toes to each foot, in the Papuan species the number is 

 generally reduced to three. The wide structural differences 

 separating the egg-laying mammals from all other members 

 of their class render it almost unnecessary to observe 

 that the spines of the echidnas are an entirely independent 

 development. Like so many of the spined mammals, the 

 echidnas have extremely short tails and thick bodies, with 

 the neck indistinctly marked. We have thus decisive 

 evidence that a more or less complete coat of spiny 

 armour has been independently acquired in the following 

 groups of mammals — viz., in the porcupines, mice, and 

 octodonts among the rodents ; in the hedgehogs and 



