April 1, 1898.] 



KNOWLfiDGe, 



91 



within, and that the reason for this excessive brightness 

 is that the edge of the spot is really protruded to a vast 

 height above the general level, and that the brilliance of 



Flii. 7. — The same viewed from identieally the same point, but 

 fillei with water. 



that part is to this extent unimpaired by absorption. 

 Now the Fig. H, already referred to, gives exactly this 

 appearance of an elevated mound with a gaping hollow, 

 which, as a matter of fact, it was. 



The appearance of a spot having a penumbra with its 

 outer margin the darkest part must be familiar to all 

 observers of sunspots ; the photosphere at some points 

 seems to overhang the spot — as it probably does. 



But there is one effect caused by this darker part of the 

 penumbra coming next the bright photosphere, and the 

 brightest part of the penumbra coming next the black 

 umbra, namely, that the centre of the spot appears to be 

 protruded outwards, in a convex manner — an appearance 

 due, in my opinion, to the deceptive shading, as it were, 

 in spots of this character, the penumbra being in reality 

 wholly concave within. 



sphere by micrometric measurement of the farther side 

 of the penumbra is not only impossible, but that the 

 results arrived at would be entirely misleading. 



As the nifiiii density of the sun is only about 1- i compared 

 with the density of water, it is evident that the vapours on 

 the solar surface cannot be of anything like the density of 

 the water in the basin ; their density, nevertheless, must 

 be very great, the attraction of the sun being more than 

 twenty-seven times that of the earth. 



j-jo. s. — The same viewed very obliquely, the bottom apparently 

 risen to the top. 



There is just one other point shown in the diagrams. 

 Figs. 1, 2, and 3, which may interest some observers of 

 sunspots. The weight of the protruded penumbra, resting 

 as it does on the photosphere (artificial), depresses_ the 

 surface not a little, so that the mouiul is resting in a 

 depression of its own making ; and if this condition of 

 the penumbra really exists on the sun, it ought to be 

 observable on the limb, as a writer m the British Astro- 

 n(miic<(l Journal for August, Mr. F. K. McDowall, states 

 that he does see it. 



The Figs. 0, 7, and 8 may serve to make clear the above 

 contention as to the probable refraction of the umbra. It 

 will be seen that, when viewed even very obliquely, the 

 black bottom (umbra) is very visible, and suffers but little, 

 comparatively, from being viewed in profile. 



It is not contended that spots are very deep relatively 

 to the sun's diameter, which is improbable, but only that 

 they are very much deeper than they appear to be ; and 

 also that to attempt to arrive at the depth of the photo- 



THE EVOLUTION OF THE VENOM-FANG. 



By Lionel Jervis. 



IT would be difficult to name a creature more feared 

 and loathed than the deadly serpent ; yet, deprived 

 of its fangs, how helpless it becomes ! It is true 

 that the great size and enormous muscular power 

 of the giant constrictors render them formidable 

 antagonists to all but the very largest animals, but these 

 monsters are comparatively rare, and are confined to a 

 limited number of species. The anaconda (Kunectes 

 murinus) from South America, two species of python 

 (P. molurus and P. nticulatus) from the East Indies, and 

 one (P. seke) from Africa, about exhaust the list of 

 unvenomed snakes dangerous to man, though the common 

 boa constrictor sometimes attains considerable proportions. 

 Generally speaking, however, the non-venomous serpent, 

 or the venomous serpent that has been rendered innocuous 

 by the removal of its fangs, is quite defenceless against its 

 enemies — and they are numerous. 



The mongoose, the hog, and many other animals — not 

 to mention man — kill them on sight. It is, indeed, 

 wonderful that the harmless species succeed in holding 

 their own in the struggle for existence, considering that 

 even the most venomous serpents frequently fall victims. 

 The hog, for instance, is said to have extirpated in certain 

 districts the rattlesnake, which is far from harmless, 

 although a very overrated creature, its sluggishness ren- 

 dering it a comparatively easy prey. The inhabitants of 

 the Lesser Antilles — at least, so the tale was told to me — 

 seem to have been unacquainted with this fact, or to have 

 overlooked it, and, arguing no doubt that if a hog would 

 kill a rattlesnake it would kill a fer-de-lance fLaclwsis 

 lanceolatus), they imported swine to keep down the pest ; 

 but that was a very different story. Then they tried the 

 mongoose ; but the mongoose does not appear to have 

 found the business good enough, and turned its attention 

 to the fowl-houses — a move which the inhabitants neither 

 anticipated nor approved. It would seem from these 

 incidents that to interview the fer-de-lance is a risky 

 commission, though I believe that the secretary bird was 

 domesticated in Martinique with a fair amount of success. 

 Thus we see that, although no doubt the object of the fang 

 is primarily to render the capture of the prey easy, it is 

 also very valuable as a means of defence. 



The first trace of this terrible weapon is found in the 

 ophistoglyphs, and to explain its gradual development in 

 this family and in the vipers, as well as in the elapine 

 and sea-snakes, it will be necessary to say something about 

 the normal dentition of serpents. Generally speaking a 

 snake has six rows of teeth, one on each side of the 

 upper jaw, one on each side of the lower jaw, and one 

 on each side of the palate : certain species have 

 teeth on the pre-maxiUary bone, but (for the pur- 

 poses of this article) this feature is unimportant. Now, 

 some snakes appear to have decided that the capture of 

 lizards, birds, and " such small deer " as formed their 

 prey would be greatly facilitated if the struggles of their 



