90 



NATURE 



[May 28, 1 89 1 



part of the Henry Draper Memorial, it is suggested that it be 

 designated as the Draper Catalogue. In order to produce the 

 spectra, a prism 8 inches square and having a refracting angle 

 of 13°, was fastened in front of the object-glass, with its refract- 

 ing angle placed perpendicular to the earth's axis. The spectra 

 obtained have been conveniently arranged in classes indicated 

 by the letters A to Q. Of these, A, B, C, and D indicate 

 varieties of Secchi's first type, E to L varieties of the second 

 type, M the third type, and N the fourth type. The letter O is 

 used for stars whose spectra consist mainly of bright lines, and 

 the letter P is reserved for planetary nebulse. The classes O 

 and P closely resemble each other, and are regarded by Prof. 

 Pickering as a fifth type of spectrum. All spectra not included 

 in these classes are indicated by the letter Q. Viewed as the 

 result of a preliminary survey of the types of the photographic 

 spectra of stars, the catalogue is of the highest importance. But 

 it is to the discussion of individual lines, which is to follow in 

 another volume, that we have to look for detailed information 

 which may improve our knowledge of stellar constitution. 



Solar Observations from January to March 1891. — 

 In Compies renchis, No. 19 (May 11, 1891), Prof. Tacchini gives 

 the following account of solar activity during the first three 

 months of this year. 



Observations of spots and faculae have been made on 64 days, 

 viz. 16 in January, 26 in February, and 22 in March. The 

 results obtained are : — 



1891. 



January 



February 



March 



Relative frequency 

 of 



Relative magnitude 



of 

 faculae. 



of days of 



spots. without spots. 



spots. „ ., 



1*56 ... 0-30 ... 18-50 ... i6-88 



2*31 ... OT5 ... 24-04 ... 89-62 



\•^^ ... 0-14 ... 11-91 ... 41-82 



1-38 

 2-38 

 I -45 



The following are the results of observations of hydrogen 

 prominences : — 



Number 

 of days of 

 observation. 



13 



22 

 17 



Prominences 



Mean 

 number. 



4-62 



7-55 

 6-12 



Mean Mean 



height. extension. 



369 

 44-1 

 40*1 



1-3 

 1-8 

 1-5 



1S91. 



January 



February 



March 



When these numbers are compared with those obtained for 

 the last three months of 1890, a marked increase is apparent. 

 In addition to this the results obtained for spots, faculse, and 

 prominences indicate that a secondary maximum of solar 

 activity occurred during the month of February. 



The Constant of Aberration. — A short time ago MM. 

 Lcewy and Puiseux described the principle of their new method 

 of studying annual aberration and the general conclusions de- 

 <iuced from the observations made last year (see Nature, 

 vol. xliii. p. 498). In Coinptes rendus, No. 20 (May 19) they 

 give a detailed account of the modus operandi, and the numerical 

 values obtained by the observation of two groups of four stars. 

 The mean of all the observations gives for the constant of 

 aberration the value 20" -447 ± o"o24. 



ANIMAL LIFE ON A CORAL REEF.^ 



TN nearly all the shallow waters of the tropical seas there is an 

 abundant fauna, but nowhere is there such a crowd of 

 marine animals of all kinds as there is in the region that extends 

 from the growing edge of the coral reef to a depth of some 

 10 or 15 fathoms beyond it. This may be due to the fact that 

 in this region there is plenty of light and heat, no great or 

 sudden changes of temperature, or of the chemical composition 

 of the water, and there is an abundant food supply brought by 

 tidal currents from the surface of the ocean. Here it is, then, 

 that we find the richest fauna. Here it is that the struggle for 

 existence is most severe, and here it is that the animals are pro- 

 tected and concealed by the most pronounced marks and colours, 

 and provided by Nature with various forms of armour, stings 

 and spines to defend them in the battles with their enemies. 

 One of the most interesting results of this severe struggle for 



' Abstract of Lecture by Dr. S. J. Hickson, delivered at the London 

 Institution, January 22, 1891. 



NO. I I 26, VOL. 44] 



existence, or perhaps it would be more correct to say of the 

 large number of species competing for existence, is the important 

 faunistic difference that may be observed between one reef and 

 another — nay, indeed, between one part of a reef and another 

 part of the same reef 



Darwin long ago pointed out that in the struggle for existence 

 a very slight advantage gained by any one of the competing 

 species may entirely alter the whole aspect of the field ; and it 

 follows that a very slight though constant difference in the 

 physical conditions, such, for example, in the case of coral reefs, 

 as rapidity of tidal currents, amount of surf or character of the 

 shore rocks, may completely change the characteristics of the 

 fauna. There are, it is true, some genera and species that are 

 apparently found on all the reefs, such as Tubipora and 

 Madrepora, but every reef has its own peculiar characters, and 

 a naturalist never feels when he is examining one that he has 

 seen something exactly like it on any previous occasion. 



The majority of the corals that are found on the reefs of 

 North Celebes belong to two great orders — the Zoantharia and 

 Alcyonaria. The prevailing colour of the living Zoantharia 

 is dull greeny-brown. The tentacles and the oral disks, and in 

 some cases the growing or younger branches as a whole, may be 

 very brightly coloured. White, pink, emerald green, violet, 

 and blue, are colours frequently met with in different parts of 

 the Zoantharian colony. The colours of the Alcyonarians may 

 be due to the bright red, yellow, or purple spicules, or to the 

 rich brown or green colour of the soft parts. There is very 

 considerable variation in the colour of the soft parts of the 

 Alcyonaria. The tentacles of the polyps of Tubipora, for 

 example, may be any shade between bright green and pinkish- 

 brown. A species of Sarcophytum, again, common on the shores 

 of Celebes, showed green and greenish-yellow and yellow 

 examples within the same half-mile of reef. All of these coral 

 colours, with the exception of the colour of the spicules mentioned 

 above, are soluble in spirit, the soft parts becoming, after pro- 

 longed immersion in this fluid, pale brown. The alcohol 

 extracts of a considerable number of corals have now been 

 submitted to spectrum analysis, and the bands they exhibit show 

 close affinities with vegetable chlorophyll. 



There is no experimental evidence at present that proves that 

 the colours of the corals, nor, indeed, of the sponges, are either 

 protective or warning in function. It seems much more probable 

 that these brilliant colours represent different stages in the building 

 up or breaking down of some complex chemical substance that 

 is always present in marine zoophytes, and performs some 

 important physiological function. 



Besides the numerous sponges, corals, holothurians, mollusks, 

 &c., that are attached to the bottom or creep but slowly from 

 place to place, the numerous species of swimming animals that 

 are capable of active movements in pursuit of prey, or escaping 

 from their enemies, must be considered as part of the fauna of the 

 coral reef. These include fishes, cephalopods, and Crustacea, 

 and those of them that seem to live habitually among the corals 

 of the reef are characterized by the possession of very curious 

 spots or stripes and very brilliant colours. 



Soon after my arrival in Talisse a large lobster was brought to 

 me marked by broad transverse bands of blue and white ; a 

 large Squilla is not uncommon marked with similar bands of 

 white and deep purple, and the little prawn Stenopus hispidus, 

 that I found in a tidal pool close to a reef, has bands of red and 

 white. The cephalopods have also peculiar markings. One 

 specimen that I found. Octopus lunulatus, had large blue spots 

 over its body and arms. The fishes, again, are marked with 

 spots and stripes of various kinds and many brilliant colours. 



Without going too deeply into the argument, we are justified 

 in saying that these animals are so marked and coloured because 

 they live among the brilliant surroundings of the coral reef; or, 

 to put it in another way, animals similarly organized and of 

 similar habits would be at a disadvantage on the coral reefs if 

 they were not so marked and coloured. The other fishes of the 

 tropics do not possess these curious and beautiful characters ; 

 the sharks, bonitos, flying fishes, herrings, and others that do 

 not live habitually on the coral reefs are not unlike in general 

 colour and ornamentation the fish of temperate seas. Again, the 

 Crustacea and fish of the tropical rivers and lakes are not as a 

 rule characterized by any peculiar colouring or marking. These 

 peculiarities, then, are not directly due to the high temperature 

 and bright light of the tropics, but they are due to the character 

 of the surroundings. 



Most of the colours must be considered to be concealment 



