RECENT WORK ON MARINE METABOLISM 7 



branched, and covered with adhesive mucus, and the animal 

 employs them to sweep through the water and capture pelagic 

 organisms which come into contact with them. The feeler, with 

 the attached food organisms, is then inserted into the mouth, 

 and the latter being tightly closed the feeler is withdrawn 

 forcibly, so that the food particles are retained. Some apparently 

 burrow in the mud, swallowing the latter like an earthworm, 

 and extracting the included nourishment. Glands secreting 

 digestive juices are described. The alimentary canal has been 

 divided into oesophagus, stomach, intestine, and rectum. 

 Muscles are described which are said to produce peristaltic 

 movements of the viscus, with the object of mixing the food 

 contents and the digestive juices. Apparently, then, we have 

 to deal with animals which nourish themselves in essentially 

 the same manner as in the case of the warm-blooded creatures. 

 So also with the function of respiration. This is said to be 

 carried out by pumping movements of the rectum (just as some 

 micro-crustacea are said to breathe), water being taken in and 

 forced out of the anus. Opening into the cloaca are the " respira- 

 tory trees," long, branched tubes, ending in fine-walled ampullae. 

 The inspired water is said to be circulated through this system 

 of vessels, and is said to diffuse through the walls of the 

 ampullae, carrying the dissolved oxygen into the ccelomic fluid. 

 Here, then, there is an apparatus to which is ascribed a function 

 essentially similar to that subserved by the gills of a fish, or 

 the lungs of a mammal — the interchange of oxygen and carbon 

 dioxide between the tissues of the animal and the surrounding 

 medium. 



These views are based on the resemblance which the struc- 

 tures in question — the alimentary canal and its glands, and the 

 respiratory trees— bear to the alimentary canal and its associated 

 glands, and to the lungs of a mammal. But does actual physio- 

 logical investigation bear out the interpretation which is usually 

 made as to the function of the organs of the holothurian? 

 Putter, 1 in a series of papers of very considerable interest and 

 importance, has investigated the exchange of oxygen, carbon, 

 and nitrogen in the case of the holothurian, Cucumaria grubei, 



1 " Studien zur vergleichenden Physiologie des Stoffwechsel," Abhandl. konigl. 

 Akad. Wissensch. Gottingen ; Math-Phys. Klasse, Bd. VI. Nro. i, 1908 ; " Die 

 Ernahrung der Wasserthiere," " Der Stoffhaushalt des Meeres," Zeitschr. filr 

 allgem. Physiologie> Bd. VII. 2 and 3 Heft, Jena, 1907. 



