of the Poly gastric Infusoria. 443 



the Polygastric Infusoria. In what follows, some other pheno- 

 mena will give support to it, and as I hope will remove any doubt 

 still remaining. 



We shall now revert to the consideration of Siebold' s view of the 

 means of nutrition in the Polygastrica. As he has separated the 

 Astoma and Stomatoda, he is obliged to search for a method of 

 explaining their nutrition. He has selected that which is most 

 ready in such cases, viz. nutrition through the common integu- 

 ment of the body. In those forms in which a mouth or gastric 

 cells filled with colouring matter have not been directly observed 

 (such are extremely few, for the latter has been observed even in 

 the Naviculce, Closterina and Monadina), we will willingly adopt 

 this obscure method of nutrition until further and more certain 

 observations have been made. But as regards the genus Opalina, 

 which Siebold has especially selected as his type in separating the 

 organs of nutrition of the Astoma, we will examine his opinion 

 on this point. He says (p. 15) : — 



" The Opalina do not exhibit an oral aperture upon any part 

 of the surface of the body, never take particles of colouring mat- 

 ter into their interior, nor can foreign solid substances, perhaps 

 swallowed as nutriment, ever be detected within them. But that 

 these Opalince are capable of absorbing fluids by means of the 

 surfaces of their body, we recognise in such individuals of Opa- 

 lina ranarum as have existed in a rectum containing a large quan- 

 tity of bile ; they have then become coloured greenish throughout. 

 If the Opalince, which require a certain amount only of moisture 

 for their existence, are placed in contact with water, they absorb 

 too much of this fluid, becoming greatly distended and gradually 

 dying. In these Opalines the absorbed moisture accumulates in 

 densely aggregated transparent vesicular drops beneath the cu- 

 taneous integument ; cavities like these filled with a transparent 

 fluid in the Infusoria have been designated by Ehrenberg as 

 gastric vesicles (ventriculi) , and by Dujardin as vacuoles." I 

 have already slightly alluded to this remark in considering the 

 mouth, and shall merely add the following. The vesicular drops 

 here spoken of by Siebold do not arise from the absorption of 

 water, for they are also seen in those specimens which have been 

 removed from the frog's intestine without the addition of water. 

 They are certainly more visible in the latter, because the animals, 

 which are somewhat folded up in the intestine, are then capable of 

 expanding themselves. Moreover, it is incomprehensible how, in 

 those individuals which have lived in an intestine filled with bile, 

 this is diffused throughout the body, but not also in such vesicles 

 as the water occurs in, or at least why the water which appears 

 in vesicular drops should not be coloured by bile in these cases. 

 The conditions of the nutrition of the Stomatoda, as detailed 



