May 1 8, 1893] 



NATURE 



The lower side of the normal flounder is uniformly opaque 

 white, like chalk. Here in the more suoerficial part of the skin 

 there is a uniform laver of iridocytes like those of the upper 

 side, opaque and reflecting, but not very silvery or iridescent. 

 Chromatophores are entirely absent. In the subcutaneous layer 

 there is a continuous deposit of reflecting tissue, to which the 

 whiteness of the skin is due, the superficial iridocytes not being 

 sufficiently thick to make the skin so opaque. 



We have shown by descriptions of the coloration elements in 

 a number of species of symmetrical fishes such as mackerel, 

 whiting, gurnard, Cotlus, pipe-fishes, &c., that the general dis- 

 tribution of the elements is constant in all, the differences being 

 in minute details. 



In chemical and physical properties the substances contained 

 in the coloration elements are as distinct as the elements are in 

 appearance and form. The black chromatophores owe their 

 colour to a melanin which is granular in its natural condition, is 

 a nitrogenous body, and is very refractory towards reagents. 

 The pigment of the coloured chromatophores is always a lipo- 

 chrome, and the absorption bands of the various lipochromes 

 obtained from the fishes examined do not differ to any great 

 •degree. The reflecting tissue was (ound always to consist of 

 guanin in the pure state, not, as has often been stated, to a 

 combination of guanin and calcium. 



These investigations of the elements and substances of color- 

 ation were undertaken in order to find out what exactly took 

 place when coloration was developed on the lower side of 

 flounders in certain experiments carried on at the Plymouth 

 Laboratory since the spring of 1890. The first experi- 

 ment was not quite conclusive, although some pigment was 

 found on the lower sides of the fish after an exposure to light of 

 four months. The second experiment was quite con- 

 clusive. Four flounders were taken on September 17, 

 1890, from a number reared in the aquarium since the 

 preceding May : they were five to six months old, and 5 to 8 

 cm. in length. They had been livingunder ordinary conditions, 

 and were in all respects normal, having no colour on the lower 

 sides. They were placed in the vessel above the mirror. On 

 one of these, two faint specks of pigment were observed on April 

 26, 1891, one died on the following July i, which showed no 

 pigment, and one on September 26, 1891. The latter was 

 t6'7 cm. long and showed only a little pigment on the posterior 

 part of the operculum. At this time one of the two survivors 

 had developed pigment all over the external regions of the lower 

 ■side, and the other had a few small spots. The first of these 

 two is still alive (March, 1893), being now three years old, and 

 it is now pigmented over the whole of the lower side except small 

 areas on the head and the base of the tail. A drawing showing 

 its condition in November, 189 1, was exhibited at the soirJe of 

 the Royal Society in 1892, and is laid before the Society with 

 this paper. The other specimen died on July 4, 1892. It was 

 then 25 cm. long and had a good deal of pigment in scattered 

 spots on the lower side. This specimen had been exposed about 

 ■one year and ten months. Several other experiments gave 

 ■similar results. 



The occurrence of abnormal coloration in pleuronectids is 

 fully considered in the memoir ; a large number of specimens 

 are described, and it is shown that there is no evidence whatever 

 that these specimens have been exposed to abnormal conditions. 

 We conclude that these abnormalities are congenital and not 

 acquired. 



We conclude that exposure to light does actually cause the 

 development of pigment in the form of normal chromatophores 

 ■on the lower side of the flounder, andaUo causes the absorption 

 of the argenteum to a great extent. We infer, in spite of the 

 occurence of congenital abnormalities, that the exclusion of the 

 light from the lower sides of flat fishes is the cause of the absence 

 of pigment from that side in normal specimens. We think that 

 the fact that the metamorphosis of the flounder takes place at first 

 normally, in spite of the light coming from below and being shut 

 ■off from above, is, in respect of the pigmentation, in favour of the 

 inheritance of acquired characters. When the exposure is con- 

 tinued long enough, the change that has taken place in con- 

 sequence of here;iity is reversed, and pigment appears. 



We consider that these investigations afford support to the 

 view that the incidence of light is the reason why the upper and 

 dorsal surface of animals is more strongly pigmented than the 

 lower or ventral throughout the animal kingdom, and that the 

 absence of light is the cause of the disappearance of pigment in 

 many cave-inhabiting and subterranean animals. 



NO. 1229, VOL. 48] 



Zoological Society, May 2.— Sir W. H. Flower, F. R.S., 

 President, in the Chair. — The Secretary read a report on the 

 additions that had been made to the Society's Menagerie during 

 the month of April ; and called special attention to a young male 

 Orang (Simia satyrus) brought home from Singapore, and pre- 

 sented by Thomas Workman, Esq. ; a White-bellied Hedge- 

 hog (Erinaceus albiventer) from Somaliland, presented by 

 H. W. Seton-Kerr ; and a female Gibbon {Hylobaies miielleri) 

 brought home from North Borneo, and presented by Leicester 

 P. Beaufort. — -The Secretary laid on the table a list of the exact 

 dates of the issue of the sheets of the Society's " Proceedings " 

 from 1831 to 1859, concerning which information had lately 

 been applied for. — Mr. P. L. Sclater, F.R.S., made some re- 

 marks on the occasional protrusion of the cloaca in the Vasa 

 Parrot at certain seasons. — Mr. Sclater also read some further 

 notes on the Monkeys of the genus Cercopithecus, and called 

 special attention to C. boutourlinii, Giglioli, from Kaffa, Abys- 

 sinia, of which he had lately examined specimens in the Zoo- 

 logical Museum of Florence, and which he considered to be a 

 perfectly valid species. — Mr. M. F. Woodward read a paper (the 

 first of a series) entitled " Contributions to the Study of Mam- 

 malian Dentition." In the present communication the author 

 treated of the dentition of the Macropodidse, and described the 

 presence of a number of vestigial incisors. Hs also showed that 

 the tooth generally regarded as the successor to the fourth pre- 

 molar was, in reality, a distinct tooth, and that the molars in 

 this family of Marsupials belonged to the second dentition. 

 — Mr. W. T. Blanford, F.R.S., read a description of two 

 specimens of a Stag from Central Tibet, belonging to the Ela- 

 phine group, on which he proposed to found a new -pecies, 

 Cervus thoroldi. These specimens had been obtained by Dr. 

 W. G. Thorold about 200 miles north-east of Lhasa, at an ele- 

 vation of 13,500 feet above the sea-level, during his late adven- 

 turous journey through Tibet in company with Capt. Bauer. 



Royal Microscopical Society, April 19.— A. D. Michael, 

 President, in the Chair. — Mr. E. M. Nelson exhibited and 

 described a mirror to be used instead of the camera lucida for 

 the purpose of reflecting the real image from the microscope for 

 drawing. — Mr. C. Rousselet exhibited a compressorium, the 

 great advantage of which was that it enabled the object to be 

 seen in every part of the field.^Mr. R. Macer exhibited and 

 described a reversible compressorium which he thought might 

 be useful. — Dr. G. P. Bate read a note on the illumination of 

 diatoms by light reflected from the cover-glass in such a way as 

 to produce a white ground illumination. — A letter from Captain 

 Montgomery, describing the abundance of ticks in the coast 

 lands of Natal, was read by Prof Bell. — Mr. H. M. Bernard 

 gave a resume of his paper on the digestive processes in 

 Arachnids. — Prof. Bell said that Mr. Bernard had made it 

 appear probable that digestion was not confined to the digestive 

 tract as usually understood, and in that case it might be that 

 they were at the beginning of a series of observations which 

 might throw a new light upon the processes of digestion. — The 

 President said he had never worked much on these groups except 

 amongst the Acarina. It was a curious thing that the distribu- 

 tion of the crystals referred to by Mr. Bernard was by no means 

 the same in different families of the Acarina ; in the majority 

 of cases they lie outside the canal altogether, and are not found 

 inside until they reach the hind gut. In the Gamasidae they are 

 poured into the cloaca. On the other hand there are families, 

 such as the Tyroglyphidse, where the crystals apparently 

 never enter the hind gut at all, but are spread through the 

 general body cavity. In the Oribatidas a medium course seems 

 to hold good, it being very difficult to ascertain where they 

 enter the hind gut. \Vhilst in the Trombididae they seem to 

 enter in a definite channel down the centre of the back. — Mr. 

 F. Chapman read a fourth paper on the Foraminifera of the 

 Gault of Folkestone. — Prof. D'Arcy Thompson's paper on 

 a Tasnia from an Echidna was read by Prof. Bell. — Mr. C. H. 

 Gill called attention to some pure cultivations of Diatoms which 

 he exhibited. 



Edinburgh. 



Royal Society, May i.— Sir Douglas Maclagan, Presi- 

 dent, in the Chair. — A paper by Mr. John Aitken, on 

 breath figures, was read. These figures are generally pro- 

 duced by breathing upon a piece of glass, on opposite sides of 

 which two coins, or a coin and a piece of metal, have been placed, 

 and have been oppositely electrified to high potentials. An 

 image of the coin is thus developed. It appeared to the author 



