6i8 



NA TURE 



[April 26, 1906 



vol. i., including the measures of nebulae situated between 

 oh. and 2h. of right ascension. The first part of this 

 volume will contain the introduction, and will include a 

 full description of the instruments and methods employed 

 in the research. 



Vol. ii., including the section 2h.-C)h., is to appear soon, 

 and will be followed by vol. iii., giving the results for 

 the region ah.-i4h. [Comptes rendus, No. 12). 



.1 Large Photographic Nebula in Scorpio. — On 

 examining the photographs obtained during his sojourn 

 at Mount Wilson last year, Prof. Barnard found that an 

 immense region near to ir and 5 Scorpii is occupied by a 

 large nebula which is comparable in size, and in 'the 

 peculiarities of its several branches, with the great nebula 

 in Orion and the extended nebulosity of the Pleiades. 



A short description of this nebula, together with a 

 splendid reproduction of a photograph of it, taken with 

 the 10-inch Brashear lens of the Bruce doublet, is given 

 in No. j, vol. xxiii., of the Astrophysical Journal. 



The nebula extends some 4^° or 5 in a north and 

 south direction, and its brightest portion lies about i° to 

 the south of 7r Scorpii. 



A striking fact in connection with this object is that 

 all the larger stars connected with it are, as might be 

 expected, of the Orion type. 



Prof. Barnard thinks that the branching, straggling 

 character of this and similar nebula; tends to discredit the 

 accepted form of the nebular theory of stellar evolution, 

 and doubts whether that theory would have ever been 

 constructed if, at the time, our present knowledge of the 

 appearance of nebulae, as shown bv photographv, had been 

 available. 



CANADIAN TIDES. 

 A PAPER on tide levels and datum planes on the 

 Pacific Coast of Canada was read recentlv by Mr. W. 

 Bell Dawson, the engineer in charge of the tidal survey, at 

 the meeting of the Canadian Society of Civil Engineers. 

 The survey of the Canadian waters on the Atlantic side 

 has been in progress now for some years under Mr. 

 Dawson's charge, and has so far advanced that permanent 

 tide gauges have been fixed at several representative parts 

 of the coast, and sufficient tidal observations obtained to 

 enable the Marine Department to issue tide tables for 

 most of the principal ports. The survey has now been 

 extended to the Pacific Coast. 



In the paper under notice the bench marks and data 

 used by the Admiralty, the Hudson's Bay Company, and 

 the town authorities on the coast have been connected up 

 by levelling, and the bench marks at Victoria, F.squimault, 

 Vancouver, and other tidal stations referred to one common 

 standard. These levels are given in the pamphlet. The 

 importance of publishing such results is emphasised by 

 the fact that the bench marks of former surveys are now 

 to a great extent useless, because thev were never made 

 public, and the level books containing "the records of these 

 surveys have been destroyed by fire, and so a large amount 

 of good work has been rendered useless, and subsequent 

 trouble and expense caused. 



The tides on the Pacific Coast are peculiar, the lending 

 feature being a pronounced diurnal inequality which 

 accords with the declination of the moon, and is subjei I 

 to an annual variation with the change in the declination 

 of the sun ; also there is an unusuaily large solar effect 

 relatively to the lunar, especially in the northern part. 

 In some parts of the coast during the greater part of the 

 day there is a long stand or only slight fluctuation near 

 high-water level, with a sharp, short drop to the lower 

 low water which occurs once in the day. Owing to this 

 diurnal inequality the two highest and lowest points in 

 the tide curve for the month may 1»- as much as five 

 days before or after the full and new moon. While the 

 tides on the Atlantic side of Canada follow the phases of 

 the moon, and accordingly the alternations of spring and 

 neap tides are the dominant features, the tides on the 

 Pacific side may be described as declination tides. 



The careful study of the tides and of the mean sea- 

 level appears to indicate that this coast is rising at a 

 rate as great as 1 or 2 feet in the century. 

 NO. 1504, VOL. 73] 



THE INTESTINAL TRACT OF MAMMALS. 

 T N a memoir " On the Intestinal Tract of Mammals " 

 (Trans. Zool. Soc. of London, xvii., part v., December, 

 1905, pp. 437-536), Dr. Chalmers Mitchell extends to 

 mammals the line of investigation which has already, in 

 his hands, yielded results of great interest when applied to 

 birds, namely, the systematic study of the pattern and 

 arrangement taken by the folds and coils of the intestinal 

 tract. With this object, the author describes the pattern 

 of the intestinal coils in a great number of mammals dis- 

 sected by him, representing examples of each of the prin- 

 cipal subdivisions of the entire class. The descriptions are 

 supplemented by an excellent series of text-figures, which 

 show the arrangements in a semi-diagrammatic, but clear 

 and accurate, manner. In the case of mammals of which 

 the author has not been able to procure specimens for 

 dissection, he quotes from the existing descriptions of 

 other authors such details as apply to the problems which 

 are the object of his investigation. Thus the memoir 

 before us gives an account, which is practically complete, 

 of what may be called the general morphology of the 

 mammalian intestinal tract, that is to say, of that portion 

 of the gut comprised between the stomach and the anus. 

 From his investigations the author arrives at a number of 

 interesting conclusions, of which only a few can be 

 mentioned in the limits of this article. 



M.iriing from an ancestral type of vertebrate, in which 

 the alimentary canal ran a straight course through the 

 body, suspended by a mesentery from the dorsal wall of 

 the body-cavity, the gut becomes thrown into a series of 

 folds as the result of a process of growth, whereby it be- 

 comes longer than the straight length between its extreme 

 points. The process of elongation can be traced both 

 phylogenetically, by a comparison of different vertebrate 

 types, and ontogenetically, in the development of any given 

 species. The more or less complicated folding of the gut 

 which results involves the dorsal mesentery, and also the 

 blood-vessels draining from the different parts of the gut, 

 which tend to take short circuits between portions of the 

 gut approximated to each other by the process of folding. 



The intestinal tract, in both birds and mammals, is 

 divided into two regions, anterior and posterior, by the 

 outgrowth at a certain point of a caecum or pair of caeca. 

 Probably in all cases a pair of caeca were primitively pre- 

 sent, as is usually the case in birds. In mammals, as a 

 general rule, a single caecum is formed, but in some cases 

 two complete caeca, or a rudiment of a second in addition 

 to the usual one, still occur. In a few cases, however, 

 all trace of a caecum has disappeared entirely. The intes- 

 tinal tract anterior to the caecum is divisible into two 

 regions, the duodenum and the small intestine, or 

 " Meckel's tract," as the author proposes to call it. The 

 latter represents only a very short portion of the primitive 

 straight gut, not more than two or three body-somites; 

 bill in nearly all birds and mammals it becomes the longest 

 portion of the gut, growing out to form the greater part 

 of what is known as the " pendant loop " in mammalian 

 embryology, and is the chief absorbing portion of the gut. 

 The intestinal tract behind the caecum may be called the 

 hind-gut, and corresponds to a much larger portion of the 

 primitive straight alimentary canal than the duodenum 

 and Meckel's tract together. In birds the hind-gut is re- 

 latively very short. In mammals, however, it is always 

 long, sometimes extremely so, and becomes divided into 

 two regions, the colon and the rectum. The colon is often 

 greatly lengthened, and thrown into loops or coils. The 

 rectum may also be considerably lengthened, but, as a 

 rule, it is not very much longer than the portion of the 

 primitive straight gut which it represents. 



In certain groups of mammals a very primitive type of 

 intestinal tract is still found. As the author points out, 

 however, likenesses which are due to the common possession 

 of primitive features, once possessed by the whole group, 

 cannot be regarded as evidence of near relationship. 

 Equally useless for proof of affinity are resemblances due 

 to the loss or reduction of parts that were once the pro- 

 perty of the ancestral stock. Clues to affinity must rather 

 lie soughl in resemblances depending on definite anatomical 

 peculiarities that are new acquisitions, and the more 



