6 SCIENCE PROGRESS 



than half of the total mass of terrestrial organisms, Patten's 



suggestion has generally been regarded as rather fantastic and 



irresponsible. 



Further, we know that some marine animals may subsist for 



quite lengthy periods in aquaria without visible food supplies, 



and this is also the case in the sea. One hardly ever finds 



food in the alimentary canal of a plaice during the months of 



December to February — a fact well known to fishermen, who 



often express surprise when they find a plaice which does 



contain food in its intestine during the latter part of this period. 



The fish during these winter months decreases in weight, and 



the loss is suggested in the formula : 



wt • U4. /• \ Length 3 (in centimetres) w „^„,. f „. 



Weight (in grammes) = - - x constant, 



ioo 



the constant varying from i to o'8. 



Now, does the fish actually exist without food during these 

 months, and does the loss of weight correspond with the meta- 

 bolic exchange which would be observed if we were to investigate 

 its physiology? We remember that it is a "semi-sedentary" 

 animal ; that its respiratory movements are slowed down during 

 the cold months ; and we conclude that it takes no food, passes 

 through a kind of hibernation phase, during which reserve food 

 materials are utilised. Nevertheless, we find that some inverte- 

 brates do appear to " starve " during certain periods, but probably 

 subsist upon dissolved food matters, and it is necessary to prove, 

 by actual measurements of the metabolic exchange between the 

 animal and its environment, that no such food sources are really 

 drawn upon. We find, however, that there are very few such 

 studies in the literature of comparative physiology. 



We may consider two instructive instances of the metabolic 

 processes that proceed in the alimentation of invertebrate 

 animals. A holothurian (or sea-cucumber) is usually stated to 

 be a predatory animal. Some species appear to live on solid 

 ground at the sea-bottom, and as they move about on the latter 

 they gather up food particles with their buccal tentacles, or 

 feelers, and brush off the latter into their mouths. Some live at 

 the bottom of deep seas, in the ooze which forms the ocean floor ; 

 and as they move about they swallow this ooze for the sake of 

 the organic remains which it contains. Others, such as Cucu- 

 maria, are said to be distinctly predatory, catching and eating 

 other animals. In these species the buccal feelers are long, 



