470 



NA TURE 



\_March 17, 18S7 



after traversing only a part of that ocean. On the other 

 hand, others are formed over the Atlantic, and especially 

 in the vicinity of Newfoundland, where there is the 

 mingling of hot and cold water, and where, as shown by 

 both air- and sea-isotherms, there is a very great differ- 

 ence of temperature in a very small area. There are 

 numerous instances both of the formation of storms and 

 also of their sudden breaking up. It is also seen how at 

 one time a storm will divide into two parts, and each will 

 follow its independent course, while at another time two 

 vvell-de\eloped storms will merge and become one. The 

 charts show how, as one of these travelling distui'bances 

 is approaching the British Islands, the weather becomes 

 unsettled, and how, as the outer edge of the front segment 

 strikes our coasts, the wind backs to the southward, and 

 in a short time rain begins to fall and the wind freshens. 

 If the disturbance passes over the British Islands, the 

 changes are generally both important and rapid, whilst, if 

 the storm area merely skirts our western coasts, as is 

 the more common experience, the changes are less 

 marked, and influence in the main only our western and 

 northern coasts. The first issue of these charts deals only 

 with the autumn, but they show very different conditions 

 of weather at the early part of this season from those at its 

 close, the whole system of weather being more disturbed 

 as the season advances. There is, however, throughout 

 the period a permanent area of high barometric pressure 

 situated in mid-.'\tlantic, on the northern side of which 

 the travelling disturbances move. This area of high baro- 

 meter oscillates from day to day within fairly well-defined 

 limits, and is very seldom altogether broken up ; and 

 doubtless a close study of the behaviour of this high- 

 pressure area will tend to nraterially advance our know- 

 ledge of the now almost hopelessly puzzling weather 

 changes with which in weather-forecasting we have to 

 combat. 



Among other points of interest exhibited by the 

 charts may be mentioned the graphic m.anner in which 

 the earlier charts show the meeting of the north-east and 

 south-east trade-winds and the seasonal march of the 

 hmits of these winds with the sun. They also show that 

 at the end of the summer the temperature of the air is 

 warmer than the sea to the extent of 2° or 3°, while, as 

 winter is approached, the sea is slightly the warmer. In 

 September there is a good instance of the formation of 

 a West Indian hurricane which eventually crosses the 

 Atlantic and passes to the north of Scotland, and the 

 chart of November i shows the vast extent of some of 

 these Atlantic storms, one gale blowing over the whole 

 ocean from the coast of America to that of Europe. 



It is scarcely possible to over-estimate the high value 

 of this series of charts. The most practical outcome 

 of their publication, it is hoped, will be an improvement 

 of our weather forecasts and storm warnings and a general 

 extension of our knowledge of the laws which regulate the 

 weather changes in our own islands ; whilst from a 

 nautical point of view they are of the utmost value to the 

 seaman in enabling him to follow in detail the many 

 changes he experiences, and they may assist him at times 

 in making a better passage. 



GILDED CHRYSALIDES^ 

 PREVIOUS WORK.—Mx:. T. VV. Wood in 1867 pub- 

 lished the observation that certain pupa; {Pieris 

 brassica:, P. rapa, &c.) resemble in colour the surface on 

 which they are found. Although this was disputed by 

 some naturalists, it was confirmed by Mr. A, G. Butler 

 and Prof. Meldola. In 1S74 Mrs. M. E. Barber published 

 some very striking observations on the colours of the 

 pupa ol Papilio niycus (South Africa), confirmation being 

 afterwards afforded by Mr. Trimen, from the case of 



' Abblract of Lecture delivered by Mr. Edward B. Poulton at the Royal 

 Institution, on Friday, February n. 



Papilio demoleus. Dr. Fritz Miiller, however, shows that 

 Papilio polydainus is not sensitive to surrounding colours. 

 The observations were explained by supposing the moist 

 skin of the freshly-formed pupa to be " photographically 

 sensitive " to the colour of surrounding surfaces ; but 

 Prof Meldola pointed out that there can be no real 

 analogy with photography. Furthermore, many pup^e 

 are formed at night, when the surrounding surfaces are 

 dark. The present investigation was undertaken with 

 the belief that the influence would be found to work upon 

 the larva as it rests upon some coloured surface before 

 pupation. 



I. Expefiments upon Vanessa lo. — This pupa appears 

 in two varieties, being commonly dark gray and much 

 more rarely yellowish-green. Six larvae placed in a glass 

 cylinder covered with green tissue-paper, produced six 

 green pupa; ; one of these, transferred to a black surface 

 while still moist and fresh, became a green pupa precisely 

 like the others. 



II. Experiments upoti Vanessa iirticce. — The pupashave 

 no green form, but appear in majiy shades of dark gray, 

 the lighter ones having golden spots on them, while the 

 extreme forms are almost covered with the golden appear- 

 ance. These latter are very rarely seen in nature, except 

 when the pupa is diseased. Over 700 pupa; were obtained 

 in the following experiments : — 



1. Effects of Colours. — Cnvvz and orange surroundings 

 caused no effect on the pupal colours ; black produced, as 

 a rule, dark pupa; ; w/iite produced light pupas, many of 

 them being brilliantly golden. This last result suggested 

 the use oi gi/t surroundings, which were found to be more 

 efficient than white, and produced pupas with a colour 

 which even more resembled gold. 



2. Mutual Proximity. — The larvse being dark, it was 

 found that when many of them became pupje on a limited 

 (white or gilt) area, the pupae were darker than when they 

 had been more isolated. The colours of each were in 

 fact affected by that part of the surroundings made up by 

 the black skins of its neighbours. 



3. Illumination. — Black surroundings produced rather 

 stronger effects in darkness than in light, but the pupK 

 were dark in both cases. 



4. Time of Susceptibility. — The mature larvae, after 

 ceasing to feed, wander (stage i.) until they find a surface 

 on which to pupate ; they then rest upon it (stage ii.), and 

 finally hang, head downwards, suspended by their last 

 pair of claspers (stage iii.), in which position pupation 

 takes place. Stage i. is variable in length, stage ii. may 

 be estimated at 15 hours (but it is also vari.xble), while 

 stage iii. is fairly constant, and lasts about 18 hours ; 

 while the whole period is commonly about 36 hours in 

 length. The larva; are probably affected by surrounding 

 colours for about 20 hours before the last 12 hours of the 

 whole period, and in this time the pupal colours are deter- 

 mined. These facts were discovered by a very large 

 number of experiments, in which larvae were placed in 

 surroundings of one colour, and then after a variable 

 time were transferred to another colour producing an 

 opposite effect. It was thus fjund that stage ii. is more 

 sensitive than stage iii., although there is some suscepti- 

 bility during the latter stage. 



5. The Part of the Larva which is Sensitive to Colour. 

 (11) The Ocelli. — The most obvious suggestion was that 



the larval eyes (or ocelli, six on each side of the head) saw 

 the colours, and, being influenced, transmitted an impulse 

 to the nervous centres which regulate the formation of 

 the pupal colours. When, however, these organs were 

 covered with black varnish, the pupa; resembled sur- 

 rounding surfaces to the same extent as when they were 

 produced from normal larvae, 



(yS) The Complex Branching Spines. — It seemed possible 

 that these structures might contain some organ which 

 was influenced by the colour, but after cutting them off 

 the larva; remained normally sensitive. 



