No. 558] 



NOTES AND LITERATURE 



taking bottom samples by means of an apparatus attached to a 

 long pole. By means of such methods he and his former assist- 

 ant compared the number of animals per square meter. Dahl 

 (1893) had made quantitative studies of the sea bottom at low 

 tide by digging and the quantitative investigations by Petersen 

 are believed by him to be the first made off shore. To improve 

 these bottom studies a new apparatus was devised for work in 

 deeper waters and the results of the present study are the first 

 product of this new device, which permits samples of the bottom 

 to be brought up in their natural position. Detritus collectors 

 were also used in these studies. With the new sampler it was 

 found that when food was abundant on the bottom there was a 

 surface layer of brown or gray, and when the food was scanty 

 this layer was black and malodorous. In view of the fact that 

 the digestive tube of most of the animals which were not vege- 

 table feeders or predaceous, contained a substance much like the 

 surface brown layer, Petersen decided to investigate this sub- 

 ject more fully. The bottom layer he calls the "dust-fine detri- 

 tus." This layer in addition to its inorganic parts consists of 

 plant and animal remains, including some plankton organisms. 

 Here then is a very much neglected source of food, and he re- 

 marks: "We have so long and so often heard of the role the 

 plankton is considered to play in the economy of the sea, that wc 

 almost forget the other sources of food, which, however, at any 

 rate in the smaller waters, certainly have even greater im- 

 portance. ' ' 



The dependence of animals upon plants for nutrition is just as 

 intimate in the sea as upon the land. Therefore to understand 

 the transformation of substance in the sea from the inorganic to 

 the various kinds of animals one must begin with the marine 

 plants. This phase of the subject was investigated by Jensen. 

 In addition to the plankton plants there are those attached to 

 the bottom, the alga' and grass wrack Zostera. The plankton of 

 the North Sea is more abundant than in the more enclosed 

 waters of the Kattegat. This plankton is not an important 

 source of organic material; the main supply on the bottom is 

 therefore either the alga? or the Zostera. Jensen shows that a 

 characteristic feature of the metabolism of the sea is that the 

 organic materials do not remain where they are formed but tend 

 to become widely distributed, more or less uniformly over large 

 areas. This might well be called Jensen's law. The vegetation 



