352 SUMMARY OF CURRENT RESEARCHES RELATING TO 



waters. The food in the sea consists mainly of (1) growing plants of 

 the benthos formation (especially Zostera and its attendant micro-flora), 



(2) detritus of dead and dying - organisms and portions of organisms, 

 and (3) animals living and dead. 



Plankton is not included as a principal source of nourishment, for 

 Blegvad maintains that the only plankton organisms which are of direct 

 importance to the fishes and bottom fauna in the Danish waters are the 

 pelagic Crustaceans and the pelagic larvae of the bottom organisms 

 themselves. Phytoplankton is of little importance save for some 

 zooplankton organisms. The great majority of the animals composing 

 the bottom fauna live on detritus, none on pure phytoplankton. 



Putter's theory of dissolved carbon compounds in sea-water is not 

 corroborated. In his calculations he did not allow enough for the 

 detritus. 



Marine animals may be grouped as pure herbivores, pure carnivores, 

 and detritus-eaters. They may be divided into those without and those 

 with hard prehensile or masticatory organs. The former include : — 

 1. Those feeding by pseudopodia (Foraminif era). 2. Those feedingby 

 ciliary currents (sponges, bivalves, ascidians, lancelets). 3. Those feed- 

 ing by means of arms or tentacles, frequently furnished with cilia 

 (many Polychrets and the Holothurians). 4. Those feeding by means 

 of a soft, generally extroversible proboscis for drawing up detritus. 



5. Those feeding by means of tube-feet (Ophiuroids and Asteroids). 



6. Those feeding by means of tentacles with nematocysts (sea-anemones 

 and zoophytes). 



Those with hard prehensile or masticatory organs include : — 1. Those 

 feeding by means of aradula (Gasteropods). 2. Those feeding by means 

 of an extroversible proboscis, furnished with hard structures (many 

 Polychtets). 3. Those feeding by means of setae-covered limbs, with 

 chitinous cuticle, and often with a masticatory gizzard in addition 

 (Crustaceans and Dipterous larvae). 4. Those feeding by means of a 

 masticatory organ with teeth (regular Echinoids). 



Detritus forms the principal food of nearly all the Invertebrate 

 animals of the sea-bottom, next in order of importance being plant- 

 food from fresh benthos plants. The value of the live phytoplankton 

 in this connexion is absolutely minimal, having little more than indirect 

 significance through the medium of the plankton Copepods. 



Organic Matter of Sea-bottom in Danish Waters.*— P. Boysen 

 Jensen corroborates the conclusion previously reached by C. G. J. 

 Petersen and himself, that the plant growths of the Zostera belt and 

 not the plankton organisms should be regarded as the principal source 

 of the organic matter of the sea-bottom in many of the Danish waters. 



The organic matter of the sea-bottom in the more sheltered waters 

 (fjords, etc.) is almost exclusively derived from the Zostera. In more 

 open waters, however, such as the Kattegat, the plankton organisms are 

 possibly of some importance as a source of origin of the organic matter 

 of the sea-floor. 



The quantity of pentosan in proportion to the amount of organic 



* Rep. Danish Biol. Station, xxii. (1914) pp. 1-39. 



