186 



KNOWLEDGE 



[OCTOBEB 1, 1891. 



cimens exliibited from time to time in the Gardens of 

 tlie Zoological Society, most of us are more or less 

 familiar with the external form of the Seals (Fig. 7), 

 and have also witnessed the exceeding gracefulness of 

 their evolutions in the water. In all Seals the limbs 

 are very short, and by the complete webbing of the toes 

 are converted into paddle-like organs. Although the 

 amount of modification is greater in the hind than in 

 the fore limb, yet in both the several digits of the 

 feet still retain their external distinctness. In the so- 

 called Eared- Seals (from which the seal-skin of commerce 

 is alone obtained) and Walruses the hind feet are 

 turned forwards beneath the body when the animal is 

 on land, after the ordinary manner. In the true Seals, 

 however (Fig. 7), these feet are always directed backwards, 

 and thus act solely as propellers in the water. All the 

 Seal tribe are clearly very closely allied to the ordinary 

 land Carnivores ; and the Eared-Seals and AValruses 

 indicate the mode in which such animals have under- 

 gone a progressive modification until the extreme speciali- 

 zation of the true Seals has been attained. 



The second group, containing the Whales, Porpoises, 

 Grampuses, Dolphins, etc., differs so remarkably from all 

 other Mammals that it has been referred to a distinct 

 order — the Cetacca. All the members of this group (Fig. 

 1) have, indeed, assumed such a completely fish-like appear- 

 ance that it is even now frequently difficult to con\ince 

 people that they are true ]\Iammals. Their mammalian 

 nature is, however, shown by their warm blood and four- 

 chambered heart, by the circumstance that they produce 

 their young in a living condition and nourish them by milk 

 drawn from the udder of the parent, and also by their 

 respiration being eflected by the aid of lungs. The " spout- 

 ing " of Whales as they come to the surface is, indeed, 

 mainly due to the water of the sea being thrown up as the 

 air from the lungs is forcibly expelled from the nostrils 

 before the animal has quite reached the surface. We may 

 add that the certainty that Whales are true members of 

 the mammalian class is one of the strongest reasons 

 against employing the term "quadrupeds" to denote that 

 division of Vertebrates. 



Although, as aforesaid, the general appearance of a 

 Whale or Porpoise is fish-like, yet a more careful examina- 

 tion shows certain very important points of difierence. In 

 (he first place, the tail-fin, or " flukes " as it is termed by 

 whalers, is expanded horizontally instead of vertically. 

 The reason for this horizontal expansion appears to be 

 owing to the necessity the Whale is under of coming 

 rapidly to the surface for the purpose of breathing ; the 

 upward and downward strokes of the powerful flukes being 

 admirably suited to effect this object with the greatest 

 speed. Then, again, the number and structure of the 

 paddles and fins is quite difi'erent from that obtaining in 

 fishes. Thus, a Whale (using this term for the whole 

 group of allied animals) has only a smgle pair of flippers 

 (Fig. 1), which correspond to the fore limbs of ordinary 

 Mammals, and to the pectoral fins of fishes. These, 

 however, although presenting certain peculiarities, are 

 evidently modifications of the normal mammalian fore 

 limb, and are devoid of any structures corresponding to 

 the fin-rays of fishes. They have lost all outward trace of 

 the digits, being completely invested in a common integu- 

 ment. Then, again, the pelvic fins of fishes are wanting ; 

 the only traces of hind limbs being certain rudimentary 

 bones found deeply bedded in the flesh of some of the 

 species (Knowledge, 1891, p. 24, fig. 2), which represent 

 the aborted hind legs of quadrupedal Mammals. If, more- 

 over. Whales have any unpaired fins the single one is 

 situate on the back (Fig. 1), and its structure is quite 



different from that of the dorsal fiu of a fish. In order to 

 enable them to stay for long periods below the surface, the 

 circulatory system of Whales develops a number of net-like 

 arrangements of the vessels in which a supply of fresh 

 blood is stored up. 



It would involve too much detail to enter into the con- 

 sideration of the numerous other resemblances existing 

 between Whales and ordinary Mammals, but there can be 

 no sort of doubt but that they are members of the class ; 

 and likewise practically none that they are descended from 

 a group of originally terrestrial forms, the special modifica- 

 tion having in this case been carried to a considerably 

 greater degree than in Seals, which we know have 

 undergone an analogous development. Naturalists are, 

 indeed, not altogether in harmony as to the kind of 

 terrestrial Mammals from which Whales have descended, 

 but the probability is that such ancestral tj'pes were more 

 nearly allied to the pig-like Ungulates than to any other 

 type of Mammals with which we are acquainted. The 

 Hippopotamus show^s us how a pig-like animal may 

 become amphibious, and there is no reason why a further 

 development should not go on. It will, however, be 

 understood that the terrestrial ancestors of the Whales 

 have long since disappeared from the face of the earth ; 

 and it should be added that not a trace of the intermediate 

 connecting forms has yet revealed itself to reward the 

 anxious search of the palieontologist. The Cetacea are 

 first known in the upper part of the Eocene di^•ision of the 

 Tertiary period, and it thus seems quite clear that they 

 were developed to fill the gap left in the life of the ocean 

 by the disappearance of the Ichthyosaurs and Plesiosaurs 

 at the close of the secondary period ; the general replace- 

 ment of a lower by a higher type of organization being 

 apparently the great life-feature by which the early part of 

 the former period is distinguished from the latter. 



THE DIAMOND MINES OF SOUTH AFRICA. 



By Yaughan Cornish, B.Sc, F.C.S. 



THE first South African diamond was found in 1867, 

 and during the next three years diamonds were 

 obtained from the river workings. In 1870, the 

 mother melt was found at Kimberley. This rock 

 occurs in pipes as they are termed, round or oval 

 funnels with a surface area of several acres, and of great but 

 unknown depth. Some have already been excavated 

 to a dex^th of 800 feet without any sign of reaching a 

 bottom, or bed rock. The rock first worked at and near 

 the surface is termed the yellow ground, a friable material 

 fo'om which the diamonds are readily extracted. When 

 the yellow ground was worked through and the hlue roek 

 struck, many of the miners imagined that the deposit was 

 worked out, and abandoned their claims. Others filled in 

 the excavations with -the ijelhm-, and sold their claims to 

 less Icnowing but more fortunate adventurers. The "blue" 

 proved to be the real matrix of the diamond, the "yellow" 

 being merely the blue rock altered by weathering, a yellow 

 colour having been produced by formation of oxide of iron 

 fr'omthe action of the atmosphere on the highlj' ferruginous 

 rock. The blue is a volcanic rock of very peculiar 

 character, extremely heavy, and of the structure known 

 as hreeciated, characteristic of a volcanic rock which 

 has been subjected to movement after hardening. It 

 contains boiflders of all sizes up to twenty tons, and 

 pieces of sandstone, shale, and occasionally fragments 

 of fossil trees. A detailed study leaves no doubt that 

 the pipes are of eruptive origin — a pipe being, in fact, 

 the neck of an old volcano — and that the blue was 



