454 SCIENCE PROGRESS. 



be hoped, lead to renewed interest in this subject ; but in 

 many respects his paper is unsatisfactory. His statement, 

 for instance, that the digestion of the gastrozooids of the 

 Siphonophore Praya is solely intracellular is inconsistent 

 with our knowledge of the processes of the digestion and 

 minute anatomy of the endoderm of Hydroid polyps, and it 

 is surprising that it should be made without some reference 

 to the work that has been done by other naturalists in this 

 group. The paper would have been of greater value too if 

 it had been accompanied by some illustrations of the pro- 

 cess of intracellular digestion in the general endoderm and 

 mesenterial filaments of the sea-anemones. 



A oreat de^l still remains to be done before it can be 

 said that we have a really clear and satisfactory account of 

 the digestion of the Ccelenterates. 



It seems to be established now that an alkaline fluid is 

 secreted into the digestive cavity of Ccelenterates which is 

 capable of emulsifying fats and converting proteids into 

 peptones, that a process of intracellular digestion also 

 occurs which is accompanied by an acid secretion, and 

 that in that process proteids are converted into pep- 

 tones, fats saponified, and starch granules dissolved. But 

 there is still some doubt as to the form in which the 

 soluble products of digestion are taken up by the endo- 

 derm, are stored for further use, and distributed through 

 the organism. 



Valuable results might probably be obtained by an in- 

 vestigation of the histology of the endoderm and physiology 

 of digestion in one of the large medusae which occur upon 

 our coasts, in which the gastral pouches give rise to fine 

 canals distributed over the umbrella. It would be interest- 

 ing to learn in what respects the endoderm in the marginal 

 ring canal differs from that of the pouches, and in what 

 form it receives its nourishment. These and other points, 

 it is hoped, will soon be taken up, and our knowledge 

 widened of this interesting and important branch of com- 

 parative physiology. 



