INrrSOBIAL ANIMALCTTLES. 39 



\rith the balls of which Ave have spoken, although the latter may get 

 into them singly, but this can only be considered as accidental. 



" We may trace the formation of these cavities, and perceive their 

 sudden and complete disappearance, with as much ease as the forma- 

 tion of the balls. Nay, more, it is sometimes possible to see how 

 one of these cavities moulds itself over a ball, and speedily after- 

 wards disappears. The microscope shows that these cavities are not 

 lined with a particular membrane, but are mere excavations of the 

 pulpy substance. They likewise often appear very near the inner 

 surface of the mem])rane which forms the skin of the animal, and 

 some of them increase to such a size that their diameter is equal to 

 the thii'd or the half of that of the entire cavity of the Infusoria. 

 The slight refraction which the rays of light undergo at their cir- 

 cumference, proves that these cavities ai'e not filled with air, but by a 

 liquid; and in the large Infusoria, it is easy to satisfy ourselves that 

 they do not open on the exterior. Similar cavities are formed in the 

 mucus of true cellular plants, pai'ticularly in certain aquatic Cryp- 

 togamia. 



" My botanical labours prevent me from carrying these re- 

 searches farther, but enough has been said to induce the naturalist 

 to pursue them. They require a great degree of perseverance, 

 for it is not easy to establish these facts in all Infusoria, but they 

 are of high importance, since the order Polygastrica has already 

 been admitted into many modern ti'eatises on Zoology." — I]d. Fhil. 

 J. vol. xxviii. 



We may add the resume given by M. Dujardin, of the views 

 entertained by him, regarding the organization of Infusoria. " The 

 Infusoria (leaving out of the question the SystoUdes or Rotatoria, 

 which are much more elevated in the scale of animals, and the 

 Bacillaria, which, along with the Closteria, are more nearly related 

 to the vegetable kingdom) have theii' origin, for the most part, from 

 unknown germs, in artificial and natural infusions, stagnant water, 

 and rivers, or such portions as rest over vegetable remains — no other 

 mode of propagation, except self-division, being well ascertained. 

 The fleshy substance of their bodies is dilatable and contractile, like 

 the muscular flesh of the superior animals, but present no absolute 

 trace of fibres or membrane, appearing, on the contrary, homogenous 



