INTESTINAL RESPIKATION IN ANNKLlhS. 815 



of food-matters. " At any rate, the actual evidence that the gills of these creatures are 

 organs which function in the absorption of foodstuff is just as strong (or as weak) as 

 the actual evidence that they take up dissolved oxygen from solution in sea-water, 



" What, then (continues Johnstone), is the function of the alimentary canal in such 

 animals as these ? Putter sugo-ests that the surface of the latter is one which is 

 instrumental in the absorption of dissolved food- matter from the sea" {i.e. it would 

 have the same function as the gills). " That it should also take in and digest solid 

 food particles, such the organisms of the plankton, may be a secondary function acquired 

 after the alimentary canal has been evolved for the absorption of liquid foodstuff. Thus 

 the capture and assimilation of diatoms by a mussel or a holothurian may be compared 

 with the captui'e and assimilation of insects by an insectivorous plant ; which latter 

 process we may regard as being strictly secondary in importance to the process of feeding 

 by means of photosynthesis of starch by the green parts of the plant." 



In later publications. Putter recapitulates his investigations and the conclusions 

 to be drawn from them (34), and extends his theory to include even Fishes (35). 

 Having shown the absorption of dissolved matters in the latter class, he infers that this 

 takes place through the gills ; the skin is not apt for absorption, and the fish swallows 

 no water ; the quantity of water passing over the gills, however, is enormous — even 

 more than is required for the purpose. The soluble matters capable of being used as 

 foods, which occur in the water, are to be considered as the mainstay of the fish's 

 nutrition. 



Putter's last communication (36) deals with certain objections to his views. 

 Henze had shown that Putter'.s methods of estimating the amount of dissolved organic 

 matters in sea-water were insufficient, and gave much too high values. Putter admits 

 this, but still holds that the quantity of carbon compounds in solution is enormously 

 greater than that of the living organisms. He returns to the subject of Actinians. It 

 is said that the tentacles are " obviously " for the purpose of taking in solid food. As 

 a matter of fact, says PtJTTER, they are not ; small animals or particles of flesh which 

 touch their surface are not seized and introduced into the a'sophagus ; on the contrary^ 

 the crown of tentacles closes over the mouth opening and protects this from the entry 

 of the so-called nutritive particles (E. Pratt, Kukenthal). Kukenthal never ob- 

 served solid nutriment in the interior of the polyps, nor saw solid food ingested ; finely 

 pounded fish-tlesh added to the water was not taken up, but the particles were 

 surrounded by a slimy secretion which caused them to adhere to the surface of the 

 colony (but cf. Carlgren's observations, referred to on p. 821 jMsf). The gastro- 

 vascular system of corals is, at least partially, excretory of the end-products of 

 metabolism. 



Putter concludes: "It has been proved (1) that the quantity of organic com- 

 pounds in solution in the sea exceeds by hundreds of times that of the animal organisms ; 

 ... (3) that animals can take up dissolved organic substances even when these are 

 present in a concentration of 1 : 280,000 to 1 : 2,000,000 ; (4) that animals can e.xist, 



trans. ROY. SOC. EDIN., VOL. XLIX. PART HI. (NO. 14). lU 



