288 SUMMARY OF CURRENT RESEARCHES RELATING TO 



c. G-eneral. 



Animal Communities on the Sea-bottom.* — C. G. Job. Petersen 

 pves an account of investigations of animal communities on the sea 

 floor. These investigations were similar to those made in Danish waters 

 and described in earlier reports. Thej were made in deep Norwegian 

 waters with a view to finding out how far the animal communities were 

 similar in Danish and JSTorwegian waters at similar depths, and what the 

 deep water might have to show as compared with shallower waters. The 

 " bottom-sampler " was used instead of the dredge, and when modified 

 so that it did not close too soon, it proved efficient at a depth of 700 m. 

 The method adopted was that of taking " profiles " of the water through 

 all depths. The conchiferous molluscs and the cchinoderms were selected 

 for the characterization of the communities, these two groups being 

 most abundant, and comparatively little subject to seasonal fluctuations. 

 Depth as such was found to have little influence on the occurrence of 

 communities ; temperature had more, but the communities themselves 

 remain constant as regards their characteristic species, notwithstanding 

 changing temperatures. Competition between nearly related species 

 is also a factor, for .closely related species of the same genus were never 

 found living on the same area of a given water. Certain small species 

 may occur as attendant species at greatly varying depths. Evidence 

 shows that there is a diminution in the amount of animal life with 

 increasing depth, and the author inclines to the belief that the pro- 

 duction in deep water is even less than the low animal content appears 

 to indicate. Full details of the " profiles " taken at the different stations 

 are given in tabular form. 



The second part of the same report contains a preliminary note on 

 the valuation of the sea, especially as regards the Kattegat. A computa- 

 tion of the quantity of eel-grass {Zostera maritima), of the " useful " 

 animals — that is, those serving directly or indirectly for human food — of 

 " useless " animals, and of food-fishes is given. It would appear that 

 the useless animals, such as Cyprina islmidica, bulk very largely, and 

 that the food supply for predatory fishes, especially for cod, which feed 

 at a higher level than plaice, is not very abundant. 



Patterns of Animals.f— J. C Mottram has analysed the patterns 

 of a number of Mammals, birds, and insects, and discusses their 

 possible value. He has been led to the following three conclusions : 

 (1) obliterative shading in animals is sometimes eilected by means of 

 pattern-blending ; (2) the outlines of animals are frequently masked by 

 the blending of patterns at or near their margins ; (3) patterns having 

 these effects are usually unlike the animal's surroundings, and do not 

 produce protective resemblance. 



Colour - change in Tench.| — H. N. MilHgan reports on seven 

 experiments on Tinea vulgaris which illustrate the readiness with 



* Eep. Dan. Biol. Stat., xxiii. (1915) pp. 3-32. 



t Proc. Zool. Soc. London, 1915, pp. 679-92 (5 figs.). 



X Zoologist, xix. (1915) pp. 387-9. 



