No. 558] 



NOTES AND LITERATURE 



383 



investigated quantitatively. Here the dominant animals are 

 small gastropods, Rissoa, Littorina, Xudibranchs, ll\)tilis. Amphi- 

 pods, Isopods and numerous animals which abound in Zostera. 

 Shoreward from this zone is the sand bottom, and finally the 

 strand, each with its characteristic animals and food habits. 

 Such a study calls to mind Mobius's description of the oyster 

 bank as a bioccenose. In discussing the food relations of these 

 communities Petersen adds a word of caution to those who in 

 the future use the word plankton. They should not use it with- 

 out stating exactly what is meant, whether plankton captured 

 by a net, that which is small enough to pass through the net, 

 and the detritus plankton. In summing up the general relation 

 of these communities Petersen remarks: "All seems to me to 

 indicate, that the greatest mass of the bottom-fauna per square 

 unit is to be found in the smaller waters, where the bottom-flora 

 occurs at least in the neighborhood, whilst the bottom of the 



oceans is as a rule to be regarded as waste regions One thing 



is certain, at any rate, the great, rich fisheries are not prosecuted 

 on the open oceans, but always in more or less close proximity 

 to the coasts or in the smaller waters." 



For a detailed study of the productivity of the different kinds 

 of bottom Petersen found it necessary to devise various forms 

 of bottom samplers, so that the mass of life for a unit area of 

 bottom might be determined. His investigations in this line 

 were begun in 1896, but his earlier results were not published. 

 His latest invention is a bottom sampler which permits one to 

 secure a specimen of soft bottom, with the layers of mud in their 

 natural position, from an area of about one tenth of a square 

 meter. The animals are taken from this sample and their rough 

 weight and dry weight are determined. The dry weight is be- 

 lieved to be the most precise estimate of the amount of life which 

 a given unit area of bottom can produce. The many difficulties 

 encountered in making such determinations are discussed fully, 

 because he was eager to make, if possible, some calculation of the 

 annual production of such a bottom. The fish are estimated to 

 consume about 3 grams per square meter, and the whelks and 

 starfish may eat twice as much food substance as the fish, or 

 about 6 grams dry weight per square meter. For the Thisted 

 Bredning, he estimates that the total amount of dry matter on 

 the bottom, is about 30 grams per square meter. He estimates 



