528 



NATURE 



\April lo, 1879 



-can assure him that, while magistrate at Point Pedro, five-and- 

 twenty years ago, I used almost nightly to see " rayons de cre- 

 puscule " in the most glorious perfection for months together. 

 Point Pedro is the extreme northern point of the i>land, with 

 a splendid sea horizon, I shall never forget the beauty of the 

 tints. E. L. Layard 



British Consulate, Noumea, New Caledonia, February i 



Salmon in Rivers of the Pacific Slope 

 In a notice of the Report of the U.S. Commissioner of Fish 

 and Fisheries, in Nature, vol. xix. p. 430, the reviewer refers 

 to the statement in a " memorandum respecting the American 

 salmon and white fish recently introduced in New Zealand by Dr. 

 Jaues Hector," that "so far as yet observed, the adult fish all 

 die after spawning and never return to the sea." The reviewer 

 writes : " We shall be glad to have some authoritative statement 

 with regard to the above fact, as without some explanation it 

 seems too extraordinary for belief." 



Dr. Hector in the above remark refers to the so-called " Cali- 

 fornian Salmon" {Salmo qtiinnat) when in its native waters. 

 There must be some exceptions to the rule as above stated, for 

 Mr. Livingstone Stone, in his evidence in the same volume {p. 

 806), testifies that in the Columbia full-grown fish of this species 

 are caught in considerable numbers, nearly exhausted, on the 

 back of the drift-nets, in July and August, but it is nevertheless 

 almost strictly true. 



In the Fraser River, British Columbia, the general opinion is 

 that the salmon never return to the sea except accidentally in a 

 dying state. The Indians, who are generally well informed 

 on -uch points, affirm this. The late J. K. Lord, in his 

 "Naturalist in British Columbia," (vol. i. p. 40, et seq.), is very 

 clear on the same point. It i>, moreover, almost certain from 

 the fumultuously rapid character of the Fraser, that the salmon 

 hatched in its upper waters — in some instances 600 miles from 

 the sea— never return there till mature and ready to spawn, and 

 that this act is their last. They show no disposition to attempt 

 to ^o back to the sea. I have seen them in great numbers in 

 s iiail streams tributary to the North Thompson, in August, spent, 

 their silvery colour turned to a livid red (with the exception of 

 the fins and tail, which are darker) but still heading persistently 

 up stream, and continuing to do so, till from sheer weakness the 

 current carried them away. In fording the brooks, the disturb- 

 ance of the water causes those possessing sufficient vitality to 

 scatter in all directions, but interrupts only for a moment their 

 dollied struggle. At this season, in most years, dead salmon 

 in great numbers are found floating down the stream, or stranded 

 on the bars and banks of the river. 



In Okanagan, Shuswap, and other lakes, there is a smaller 

 fish, which may be a "land-locked" salmon, but of which I was 

 n t able to preserve specimens. The Indians say that it does 

 n it come from the sea, but lives in the deep waters of the lake, 

 till in August it enters certain streams to spawn. Like the 

 salmon it becomes, when spent, first blotched with pale red, and 

 eventually altogether of that colour and without silvery lustre, 

 the flesh at the same time losing its pink tint. It possesses the 

 same instinct of struggling against the stream till it dies. I have 

 seen them in brooks within a stone's throw of the lake, endea- 

 vouring with their remaining strength to keep themselves from 

 being carried back into it. 



Lord makes an exception of the "fall" or "dog-tooth" 

 almon {S. lycaodon), of which he supposes some go back to the 

 sea, and return to the rivers in following years. It remains, 

 "lowever, an undoubted fad, that by far the greater part of the 

 prodiifious number of salmon entering the Fraser every year, 

 i>t-rish. The fish appears to refuse food, and is not caught in 

 the river by bait or fly, though frequently taken by trolling with 

 fish or spoon-bait in the salt water. 



It is much to be desired that a systematic investigation of the 

 species of salmon frequenting the Fraser and other rivers of 

 Itpitish Columbia should be made, embracing their habits and 

 ilie course of their migrations. The subject is an interefting, 

 but very intricate one. George M. Dawson 



CJeological Stu-vey of Canada, Montreal, March 27 



The Marsupials of Australia 



The peculiarities of the structure of the marsupials of Ans- 



fralia are so remarkable and their habits are so unlike those of 



the placentals of the Old World, that probably no apology is 



ceded for venturing to lay before your readers a short account 



of one of these peculiarities possessed by certain genera, which 

 I believe has escaped the observation of most naturalists, and 

 may prove interesting to some of your subscribers. 



The inferior maxillary or lower jaw-bone of almost all known 

 mammals consists of two bones united together with more or less 

 rigidity by a strong cartilage, which allows no play or inde- 

 pendent movement whatever, and which practically firmly unites 

 them into one bone. 



The formation of the inferior maxillary of the Macropidse, or 

 kangaroos, is an exception, however, to this rule ; instead of 

 being united by a cartilage, the two rami of the lower jaw are 

 jointed at their point of contact with a hinge somew hat resembling 

 that upon which the two shells of a bivalve move, that is, upon 

 corrugations which project from the two edges and fit accurately 

 into one another. 



These two rami extend a short distance beyond the point of 

 contact, and into their terminations are fixed two long procum- 

 bent incisor teeth, the only two incisors possessed by this family 

 in the lower jaw. Immediately in front of this joint, that is, at 

 the root of the procumbent incisors, a circular muscle embraces 

 the two rami of the jaw, the contraction of which has the effect 

 of bringing the inner edges of the procumbent teeth together ; 

 upon its relaxation or the contraction of another set of muscles, 

 placed probably at the extremities of the rami, where they hinge 

 upon the facial bones, the incisors are separated the extreme dis- 

 tance allowed them by the ligaments around the joint. The 

 action of separating the teeth is probably connected in some 

 measure with the action of opening the jaws, as I not unfre- 

 quently found that when the mouth was widely opened, the teeth 

 themselves became separated. 



The muscular action of uniting the incisors may be said to be 

 exemplified in the case of a pair of shears when the blades are 

 closed by a grasp of the hand, and the force is applied between 

 the fulcrum and the point of resistance. 



In Prof. Owen's work upon the "Anatomy of the Vertebrates," 

 the following passage appears, showing that he was aware of a 

 certain looseness of connection of the two rami, but probably 

 not aware of the completeness of the construction with its 

 separate functions. After certain references to the wombat he 

 says, "In other marsupials the rami of the lower jaw are less 

 firmly united at the symphysis ; they permit independent move- 

 ments of the right and left incisors in the kangaroos, and in the 

 opossum both the rami of the low^er jaw and all the bones of the 

 face are remarkable for the loose nature of their connections." 



In the work upon " Odontography" by the same distinguished 

 writer, various references are made to the lower incisors of the 

 macropidse, but his readers are in every ins: ance led to believe 

 that their trenchant margin is their outer edge, and I believe it 

 has escaped his observation altogether, that the inner imargin 

 where the two teeth come in contact has the principal cutting 

 edge, 



Mr. G. R. Waterhouse was aware of the inner trenchant 

 margin as in his " Natural History of the Mammalia," he refers to 

 these incisors as having " cutting external and internal margins." 

 P'urther on he says — " In Macropus tnajor (and, perhaps, in some 

 nearly allied species), the rami of the lower jaw are loosely 

 attached at the chin, and at the apex they are free, and the 

 animal has the power of slightly separating the lower incisors, 

 so that their outer cutting edges are brought more closely in 

 contact with the upper incisors than they otherwise would be." 

 Were this, however, the only utility of the loose attachment at 

 the symphysis, what function has the cutting inner margin to 

 perform ? 



An examination of those incisors will disclose the following 

 facts : — 



If the jaw of one of the macropidae is examined immediately 

 after death, when the muscles are relaxed, it is found that the 

 smallest pressure upon the base of the rami suffices to open 

 the lower incisors to the extent of about one -fourth of an 

 inch in larger specimens, and about one-eighth in the 

 smaller Pademelons or Halmaturi. The inner edges of the 

 procumbent teeth will then be seen to be sharp, but strongly 

 supported by a considerable thickness of enamel immediately in 

 rear of the edge, and when the teeth are united by the contrac- 

 tion of the muscles, they fit so perfectly throughout their whole 

 length that they will grasp a hair at any point between the base 

 and the apex. On the other hand, the outer margins of these 

 teeth are blunt and somewhat rounded, and when the jaw is 

 closed and at rest, instead of fitting on to the teeth of the upper 

 jaw, as represented in diagrams in Owen's " Odontography," the 



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