August 



1913] 



MATURE 



59; 



The apparatus has been mainly used as a check 

 upon observations in the ponds. 



For observing and photographing life on the 

 bottom, I use a tube 3 ft. long, with a glass partition 

 inside, a foot from the end. This apparatus acts as 

 a boat-like sea telescope, and is fitted with a camera. 

 Lastly, through the kindness of Prof. Herdman, 1 

 have established at Port Erin a large wooden tank 

 above ground. Three sides oi the tank incline at an 

 angle ol 4^ : ; the fourth is perpendicular. In the 

 perpendicular side is a glass window, and attached to 

 it an observation box, o ft. by 4 ft. The tank and 

 observation box revolve together on a platform; by 

 1 liis means an object in the tank can be seen by 

 reflected and transmitted light at will. 



It is usual to consider pigmentation as the main 

 factor in the concealment of subaquatic life. Among 

 organisms that live in more or less the same character 

 of surroundings, pigmentation is undoubtedly most 

 important; but in the forms of life that are constantly 

 changing their environments, the best concealed are 

 those that most effectively reflect their surroundings. 



When, however, an organism depends mainly upon 

 reflection for its concealment, the reflection of litjht 

 from above has to be modified, or cist- the organism 

 is revealed. In some forms of life, particularly fishes, 

 pigmentation upon the back is the method of modify- 

 ing this reflection from above. In oilier forms this 

 top light is cut off by position, e.g. in light-coloured 



It will be noticed thai the white serpula on the 

 rock reflects in the same manner; and as the light 

 parts of rock also appear ol a greenish colour the 

 anemone and the serpula are practically invisible. 

 Advisedly I say practically invisible, for the greenish 

 anemone when closed makes a uniformly shaded green 

 mass against a patterned rock. 



It will have been noticed that the red stick holding 

 tin- white card, when seen from under the water in 

 green surroundings, appeared a dull black. 



When Tealia crassicornis la red and white anemone) 

 is attached to the under-surface of a rock with a 

 green coloration below, the whites of this anemone 

 appear green and the red markings appear dark, so 

 that now the anemone shows a general green colora- 

 tion with dark markings upon it, which fit in with 

 the dark markings on the stone. Many forms oi 

 light-coloured marine life are found under shelving 

 rocks. I consider they escape destruction in this 

 position owing to the fact that they reflect their 

 surroundings. 



Next let us consider the modification of reflection 

 by pigmentation. This is best illustrated in fishes. 

 Until one has observed fish by entirely natural illu- 

 mination, it is difficult to realise how important a 



. nemoni s, which are only to be found attached to the 

 under-surface of shelving rocks. 



Before proceeding further, 1 would like to illustrate 

 the appearance of a while object, as seen from under 

 the water. I show a sheet of white cardboard pinned 

 on a red stick, which in turn was stuck in the centre 

 of an empty pond. The sides and bottom of the pond 

 were covered with green conferva?. In this position 

 the card appeared white, and incidentally the stick red. 



The pond was then filled up with water, and now 

 the white card so exactly reflected the colour around 

 that it became practically invisible, vet its position 

 was revealed by a streak of light along the upper 

 edge of the card. 



In nature all white subaquatic organisms reflect in 

 a similar manner, and white is never seen under the 

 water, except when there is no provision made for 

 modifying the reflection of light from above, or when 

 iii 'ganism turns on its side. 



As an illustration of this point, let us consider the 

 white anemone (Actinoloba dianthus). I show a 

 colour-plate of this anemone attached to the top of 

 a rock and, of course, it appears white, but as soon 

 as it moved only a distance of 2 in. under the shelving 

 edge of the rock, the top light was cut off, and you 

 will see the white anemone appears green as it 



II d the prevailing colour below. 



NO. 2284, VOL. Ql] 



part reflection plays in rendering both silvery and 

 highly pigmented fishes inconspicuous. 



The silvery fish does not appear silvery, but red, 

 brown, or green, according to the general colour 

 around, and in addition it will reflect upon its body 

 stem for stem the reeds into which it has rushed in 

 order to hide itself. 



As an illustration to show how a highly pigmented 

 fish reflects light, I show a tench, only o in. under 

 the water, anct it will he seen the dark back appears 

 quite silvery. 



Pigmentation on the back conceals a fish against 

 the bottom, but undoubtedly the important function is 

 to conceal it, for protective and aggressive purposes, 

 from other fish on the same level as itself. I would 

 point out that the same light which is reflected from 

 the sides of the fish, through the eye of the fish, con- 

 trols the amount of contraction of the pigment cells 

 on the back : thus the reflection from above is cor- 

 rectly modified, and the fish is rendered a uniform 

 shade. Rut this uniform shade only conceals against 

 a uniform background. 



Thaver has shown in the animal world how th 



