106 



KNOWLEDGE 



[May 1, 1894. 



thread the beautiful gloss which is one of its strongest 

 attractions ; and finally, the composite fibre thus made issues 

 at the pore of the papilla and speedily hardens. In form- 

 ing the more compact portion of the cocoon, the caterpillar, 

 which is of course inside at the time, bends its head over 

 its back and sways it backwards and forwards, tracing out 

 with its silk a series of figures of eight which adhere to 

 one another by reason of the stickiness of the thread when 

 fresh foiTfled. When a patch of silk has thus been laid 

 down in one position, another is similarly placed else- 

 where, and so on till the cocoon acquires the requisite 

 thickness all over. The amount of silk used depends upon 

 the amount and nature of the food on which the insect has 

 been reared. Sometimes as much as half a mile of silk 

 may be unwound from a single cocoon, and it is easy to see 

 what a vast amoimt of work the laying down of such a 

 length entails upon the caterpillar, and what an enormous 

 number of times it must sway its head backwards and 

 forwards through the narrow limits of its silken envelope 

 before its toils are over. 



(To be continued,.) 



ANCIENT AND MODERN HIPPOPOTAMI. 



By E. Lydekker, B.A.Cantab. 



THE popular conception of hippopotami is that they 

 are clumsily-built creatures of enormous size and 

 bulk, spending the greater portion of their time in 

 the rivers and lakes of Africa, where they are 

 more at home than on land, diving with the 

 readiness of a crocodile, and even walking on the river 

 bed with their bodies submerged many feet below the 

 surface of the water. As regards the common hippo- 

 potamus (Hippopotamus amphiiius), which is the one that 

 has alone been exhibited in our Zoological Gardens, and 

 portraits of which we are enabled by the courtesy of the 

 Secretary of the Zoological Society to present to our 

 readers, this conception is a perfectly true one. As, 

 however, is so frequently the case in popular zoology, this 

 conception, excellent as it is so far as the common species 

 is concerned, does not cover the whole ground, for it 

 happens that there exists in Liberia a second species of the 

 genus, known as the pigmy hippopotamus (H. lihcnimsis), 

 differing not only in size, but likewise in habits from the 

 one with which we are all familiar. In place of attaining 

 a total length of about eleven feet, measured in a straight 

 line, and weighing probably some three or four tons, the pigmy 

 hippopotamus is not larger than a good-sized wild boar, 

 although it has the short and stout limbs of its gigantic 

 cousin, with which it also agrees to a certain extent in the 

 relatively large size of its head. As regards its mode of 

 life, this species differs, however, in toto from the common 

 one. Instead of passing at least as much of its time in 

 the water as on land, and never living away from rivers or 

 lakes, the pigmy hippopotamus is an inhabitant of the 

 dense tropical forests of that part of western Africa which 

 is its home, where it apparently leads a life very similar to 

 that of wild pigs, wallowing in swamps after the manner 

 of those animals, but apparently not habitually frequenting 

 rivers, though it is doubtless, like almost all mammals, 

 able to swim well when the necessity arises. Moreover, 

 in place of associating in large herds after the manner of 

 the common species, and never moving far from one 

 particular locality, the Liberian hippopotamus is a com- 

 paratively solitary creature, gomg about at most only in 

 pairs, and wandermg long distances through the woods, 

 where it seems to have no definite place of abode. 



Out of a large number of representatives of the genus 

 once widely spread over the Old World, the common and 

 pigmy hippopotami, both of which are confined to Africa, 

 are the only species which have survived to the present 

 day ; and the reader will at once see, when we have to take 

 into consideration the probable habits of the extinct kinds, 

 how fortunate it is that these two widely different forms 

 have been preserved to us. Were there only the common 

 species, we should have had no conception that any 

 hippopotamus possessed the habits characterizing the 

 smaller kind, and might thus have been led into drawing 

 very erroneous inferences as to the mode of life and habitat 

 of fossil hippopotami. 



The general appearance of the common hippopotamus is 

 so familiar to all, and is so well portrayed in our illustrations, 

 that we need not spend much time in discussing it. We 

 may observe, however, that the enormous size of the head, 

 and especially the great width of the mouth, the prominent 

 position of the eyes and nostrils, the minute ears, bulky 

 body, short and stout limbs, and short tail, are among the 

 most striking external features of the creature. The 

 presence of hoofs (four in number on each foot) shows that 

 the hippopotamus belongs to the great order of hoofed, 

 or ungulate, mammals, and the thickness of its nearly 

 naked hide led the older naturalists to place it among what 

 used to be called the pachyderms. It has been shown, 

 however, by anatomical investigations that the group 

 thus designated, which included such totally different forms 

 as elephants, rhinoceroses, and hippopotami, is an entirely 

 artificial one, and that hippopotami, together with their 

 near relatives the pigs, are much more closely connected 

 with the ruminants, the distinctive characters of which 

 have been already indicated in an article in this journal. 



The young hippopotamus represented in the fuU-page 

 plates was born in Antwerp in September, 1891 ; while 

 the large female depicted in our third and fourth 

 illustrations is of English birth, having been born in the 

 Zoological Gardens on November 5th, 1872, and accord- 

 ingly named " Guy Fawkes." In both instances, Mr. 

 Ranyard, by whom the photographs were taken, has 

 been successful in showing the characteristic form of the 

 head. 



If the reader desires to know why zoologists place such 

 very dissimilar-looking animals as the hippopotamus and 

 the giraffe in the same great group, while they simder 

 from the former the apparently more similar rhinoceroses, 

 we reply that this is largely due to the difference in the 

 structure of the feet of the two gi'oups. In that the bones 

 of the skeleton of the two middle toes are symmetrical to a 

 line drawn between them, the hippopotami and pigs 

 resemble the ruminants, whereas the rhinoceroses agree 

 with horses in having the middle toe (which is alone 

 present in the latter) symmetrical in itself. Those of our 

 readers who read the article above referred to may recollect 

 that one of the essential characteristics of the ruminants 

 is the circumstance that in the lower part of the leg 

 the two middle toes are supported by a single bone 

 known as the cannon-bone, which consists anatomically 

 of two originally distinct elements welded together, 

 while the supporting bones of the small lateral toes are 

 incompletely developed. If, on the other hand, we examine 

 the skeleton of a hippopotamus, we shall find that in each 

 foot the four nearly equal-sized toes are severally supported 

 by four complete and distinct bones, known in the fore 

 limb as the metacarpals and in the hind limb as the 

 metatarsals ; and it will be obvious that this is a much 

 simpler or generalized type of foot-structure than that 

 which characterizes the ruminants. If, again, we con- 

 trast the foot of a hippopotamus with that of a pig, we 



