ON DIGESTION IN THE CCELENTERA. 



THE science of Comparative Physiology is one which 

 has not yet received the attention which it deserves 

 from those engaged in biological investigations. The facts 

 of the anatomy and development of a large number of 

 animals are now well known, but we are still in possession 

 of very little information concerning" the physiological pro- 

 cesses of digestion, respiration, circulation and the like of 

 the commonest and best known creatures which are dis- 

 sected in our laboratories. 



A special word of welcome, therefore, must be given to 

 any piece of careful and conscientious work in this line of 

 research, and the hope expressed that the work will be 

 continued and extended. 



The subject to which some attention has been paid 

 during the last few years, and in which it may be said some 

 little progress has been made, is that of the digestive pro- 

 cesses in the Invertebrata. 



Although the investigation received its most important 

 stimulus from the researches of Metschnikoff on the di- 

 gestion of various groups of invertebrata, the interest has 

 been somewhat concentrated of recent years upon the 

 endeavour to determine accurately the physiology of the 

 digestion of Ccelentera, and it may be of some interest to 

 the readers of this journal to have in the form of a short 

 essav some account of the more recent investigations on 

 this branch of the subject. 



In the year 1880, Metschnikoff proved that the en- 

 doderm cells of many hydroid polyps, sea-anemones and 

 other Ccelenterates possess the power of throwing out 

 processes of their protoplasm, embracing particles of car- 

 mine and the like, and thus incorporating them into their 

 substance. These particles of carmine are not of course 

 digested by the endoderm, but the conclusion was drawn 



that the cells have in like manner the power of enclosing 



32 



