224 



KNOWLEDGE. 



[December 1, 1892. 



are the five toes of the hind limb. As -we have already 

 mentioned, almost the only feature ^vhich the aa-rd-vark 

 has in common -nith the armadillos is the absence of front 



Fig. 3.— The Ethiopian Aard-Tavk. (From Sclater, Proc. Zoo}. Soc.) 



teeth, and its cheek-teeth are quite unlike the simple ones 

 of the latter, as, indeed, they are dissimilar to those of any 

 other mammals. In the first place, they are preceded by 

 a functionless series of milk-teeth (a featiu-e found else- 

 where among edentates only in one species of armadillo), 

 while in the second place the premolars are unlike the 

 molai's. The latter are composed of a number of closely 

 packed denticules, each furnished with a central pulp 

 cavity, and by their close approximation forming polygonal 

 prisms, so that a cross-section of one of these teeth 

 presents the appearance of a pavement. No dental struc- 

 ture among mammals is at all comparable to this, although 

 there is some approximation to it among certain fishes. 



Of the two living species of aai'd-vark, one is confined 

 to South Africa, while the other (represented in our figure) 

 inhabits part of Egypt and other districts in the north- 

 western portion of the same continent. A third species 

 occurs fossil in the pliocene deposits of the Isle of Samos, 

 but with this exception the paheontological record is silent 

 as to the past history of these strange creatures, as to 

 whose origin and relationship to the other animals we are 

 at present utterly in the dark. Indeed, the aard-vark is 

 placed among the edentate mammals chiefly because 

 zoologists do not know where else to put it, and they take 

 that group as a kind of refuge for the destitute. Were it not 

 that the burdening of zoological science with new names 

 is from all points of view to be deprecated, there is, indeed, 

 much justification for regarding these animals as the sole 

 representatives of a distinct order, but, although in some 

 ways such a new departure would be convenient, I do not 

 know that in others it would be of any great advantage. 

 But in including them provisionally among the edentates 

 we have to recollect that their afiinities with other mem- 

 bers of that group — not even excepting the pangolins — 

 must be extremely remote. 



Aardvarks lead what would seem to us a very dull and 

 monotonous kind of life, passing the whole of the day 

 curled up in their deep burrows, which are generally ex- 

 cavated hard by the tall pyramidal hills made by the 

 tei-mites, and only issuing forth at night to dig in the 



mounds for their favourite insect-food. Not a great many 

 years ago it used to be said at the Cape that wherever a 

 clump of termite hills was to be seen there an aard-vark's 

 burrow might be pretty confidently ex- 

 pected. Unfortunately, however, as we 

 learn from a recent report of the Agri- 

 cultural Department of the Cape Colony, 

 this is no longer the case, and the aard- 

 vark of that district runs a good chance 

 of being exterminated at no very distant 

 date. 



This deplorable result is being brought 

 about by the incessant pursuit of these 

 animals by the natives for the sake of 

 their hides and flesh, and also to their 

 being dug out by Europeans for so-called 

 sport. Their flesh is said to be excellent, 

 and is compared to superior poi'k ; while 

 the value of each hide is about fifteen 

 shillings. This threatened extermination 

 is a very short-sighted policy on the part 

 of the South African farmers, to whom 

 the aard-vark (as the report before us 

 points out) is a valuable ally, not only 

 on account of the enormous number of 

 termites it consumes, but likewise from 

 the circumstance that while it is engaged 

 in digging for these insect-pests it covers 

 with loose earth a quantity of the seeds 

 of grass and other pastoral herbage which would otherwise 

 perish during the hot season. Although there is no 

 likelihood at present of the Ethiopian aard-vark sharing 

 the threatened fate of its southern cousin, yet the extermi- 

 nation of the latter would be a sad loss to zoological 

 science, and we therefore wish every success to a movement 

 which we hear has been set going by the Cape Farmers' 

 Association for the protection of this most strange and 

 curious creature ere it be too late. 



ON THE DISTRIBUTION OF STARS IN THE 

 MILKY WAY. 



By John Eichabd Sutton, B.A.Cantab. 



S' 



EVEKAL considerations seem to point to the con- 

 clusion that the galaxy must be generally of a 

 roughly circular section ; for if we imagine the 

 true depth of the galaxy along the line of sight to 

 be considerably greater than its true breadth (a 

 form to which Sir John Herschel inclined after his study 

 of the stars in the southern hemisphere), we should have, 

 since the sides of such a figure would probably not be 

 smooth, but would be crowded with excrescences and 

 streamers, a great degree of brightness along the central 

 line of the Milky Way throughout its whole length, and a 

 rapid shading oti' to the edges ; and the greater the depth 

 of the Milky Way along the line of sight, the more would 

 this aspect be exaggerated. On the other hand, if the 

 galaxy be of roughly circular section, the decrease of 

 brightness would be much mqre gradual — which is indeed 

 the case. 



Perhaps Figs. 1 and 2 will make this clearer. Let S be 

 the sun ; SA, SB, SC, SD, lines in a plane through the 

 sun at right angles to the direction of the galaxy G ; 

 a, b, c, streamers. We see that in Fig. 1 the brightness 

 along SA and SD would be considerably less than along 

 SC, which again would be considerably less than that 



