230 SEA-SIDE STUDIES. 



In one piece from which I had expressed all the fluid 

 I could, the decrease was slight, and the food was 

 soon rejected. But in every case the delicate skin of 

 the ventral portions of the mackerel and whiting were 

 uninjured. The fine metallic lustre was untouched, and 

 the skin unbroken ; showing that the digestion does 

 not consist in appropriating the substance of the food 

 given, but in expressing the juices contained therein." 

 I dare not pause now to touch upon the many topics 

 which are suggested by the conclusion to which these 

 investigations led me. It will be enough just to note 

 here the progressive complication of the digestive 

 function in the progressive complexity of the animal 

 series. Starting from the simple cell, which draws its 

 nutriment from the plasma surrounding it, by a simple 

 process of endosmosis, we first arrive at the mouthless 

 Actinophrys, or the Amoeba, which, folding its own 

 substance over the food, presses out such nutriment as 

 it can ; we then reach the Infusory with a mouth, 

 but without stomach of any kind ;* and the Polype, 

 which has a portion of its integument folded in, serv- 

 ing both for mouth and stomach, but not anatomic- 

 ally differing from the external integument, nor phy- 

 siologically differing in its action from that of the 

 Amoeba's gelatinous substance ;-|- we then ascend to 



* Nobody now beHeves in Ehrenberg's Polygastrica, or many- 

 stomached animalcules. 



+ Trembley turned a Hydra inside out, and found the outside per- 

 form the function of a stomach. This has been held as proof that a 

 mucous membrane is only a reflection of the skin. But from what has 



