rOLYGASTRIA. 25 



gorging a goat or other animal much thicker than the snake itself ; 

 for doubtless the little cavities successively receive and digest, like 

 the stomach of the boa, the dissolved parts of the swallowed prey. 

 But it has been further objected that the cavities are not fixed in 

 definite positions, but are seen constantly, though slowly, moving, 

 and apparently rotating through the general cavity of the animal. 

 This phenomenon, first observed by Focke in 1835*, led him to dis- 

 sent fi-om Ehrenberg's aecount of the alimentary canal, at least in re- 

 gard to the Loxodes Bursaria, in which not only the balls of coloured 

 food, but the green corpuscles, which are constant elements in the 

 organisation of the animalcule, are subject to a regular circulating 

 movement, like the granules of chlorophyll in the leaf-cells of the 

 Valisneria spiralis : both food and granules being carried along by 

 the corresponding motion of the gelatinous fluid or plasma in which 

 they are suspended. 



Analogous phenomena observed by Rymer Jones f, Meyen;):, Erdl§, 

 and Siebold||, have accumulated a body of evidence against Ehren- 

 berg's determinations which the sub-circular arrangement of the 

 food-filled spaces in Vorticella, and their subspiral disposition in 

 Leucophrys, are inadequate to repel. The only expressly organised 

 internal digestive apparatus in the stomatode Polygastria is a simple 

 wide and very dilatable cavity {Jig. 18. a.), extending into the middle 

 of the body from the mouth'; having a ciliated inner surface in Loxodes, 

 and probably other species. The spaces in the surrounding soft 

 tissue into which the digesting parts of an engulphed prey, or the 

 particles of carmine and indigo, pass, are usually filled -with a clear 

 fluid, and they have no constant and specially organised canals of 

 communication with the common digestive cavity. In some species 

 this cavity has a second opening or anal outlet {Nassula elegans) : 

 in most species the same opening serves both as mouth and vent. 



Although a vascular system with proper parietes has not been 

 detected in any Polygastrian, all the species which possess a mouth 

 and digestive cavity also manifest one or more pulsating vesicles, 

 varying as to shape and position in the different species. During the 

 diastole the vesicle is filled by a clear colourless fluid ; in the systole 

 it disappears. The fluid is the product of the digestive process, and 

 answers to both chyle and blood in the higher animals ; by the action 

 of the pulsatile cells it is driven through the soft parenchyme and its 

 stagnation there is prevented. In the genera Vorticella, Epistylis, 

 Loxodes, in Amceba diffluens, ParamcBcium Kolpoda, Stylonychia 



* XX. p. 785. t ^^- p- 121, X xxn. 



§ XXnL B XXIV. p. 16. 



