262- • DR WALTEll H. GASKELL. 



admirable paper by Hardy and M'Dougall,^ which does not 

 appear to be widely known. Hardy succeeded in feeding 

 Daphnia with yolk of egg in which carmine grains were mixed, 

 and was able in the living animal to watch the whole process 

 of deglutition, digestion, and absorption. The food, which is 

 made into a bolus, is moved down to the middle region of the 

 gut, and there digestion takes place, then by an antiperistaltic 

 movement the more fluid products of the digestion process are 

 sent right forward into the two anterior diverticula, where the 

 single layer of columnar cells lining these diverticula absorbs 

 these products, the cells becoming thickly studded with fat 

 drops after a feed of yolk of egg. The carmine particles, which 

 were driven forward with the proteid and fat particles, are not 

 absorbed, but are at intervals driven back by contractions of 

 the anterior diverticula to the middle region. 



These observations prove most clearly that these anterior 

 diverticula have a special nutrient function, being the main 

 channels by which new nutrient material is brought into the 

 body, and, as pointed out by the authors, it is a remarkable 

 exception in the animal kingdom that absorption should occur 

 in the portion of the gut which is anterior to that in which 

 digestion occurs. In all these animals these two anterior diver- 

 ticula extend forwards over the brain, and, as we have seen in 

 Branchipus, their anterior extremities are so intimately related 

 to a part of the brain — viz., the retinal ganglion — as to form a 

 lining membrane to that mass of nerve cells ; it follows, there- 

 fore, that the nutrient fluid absorbed by these cells must be 

 primarily for the service of the retinal ganglion. In fact, the 

 relations of this anterior portion of the gut to the brain as a 

 whole suggest strongly that the marked absorbing function of 

 this anterior portion of the gut is in order to supply in tlie 

 first place nutrient material to the most vital, most important 

 organ in the animal— the brain and its sense organs. This con- 

 clusion is borne out by the fact that in these lower Crustaceans 

 the circulation of blood is of a very inefficient character, so that 

 the tissues are mainly dependent for their nutrition on the 

 fluid immediately surrounding them. It stands to reason that 



^ " On the structure and functions of tlie alimentary canal of Daphnia," Pruc. 

 of Camiridge Pldlosopli. Soc, vol. viii. ji. 41, 1893. 



