or THE PROTOZOA. CTLIATA. 311 



existence of a sense of taste. Indeed, in the case of minute plants we per- 

 ceive a similar apparent selection of localities abounding in appropriate nutritive 

 matters. Another assumed vital characteristic was, that Cihated Infusoria 

 have a feeling of company (a fondness for society), inducing them to con- 

 gregate together, — an idea requiring considerable effort of imagination to 

 conceive, but which, we fear, -will scarcely find acceptance as a fact by any 

 person who will look abroad for parallel instances of the congregating together 

 of the same organisms ; and plenty such are at hand, even among the lowest 

 plants. 



Dextal AppAEATrs, OR Teeth. — Before quitting the subject of digestion and 

 of the digestive organs, some notice must be taken of the pecuHar formations 

 considered by Ehrenberg to represent a dental apparatus concerned in the 

 preparation of the food for digestion. This apparatiLS occurs in the form of 

 a cyhnder of apparent bristles (XXIV. 282, 2m, 308, 309 ; XXIX. 48)— 

 the supposed teeth — placed behind the mouth, as seen in Ohilodon (XXIX. 

 48), Nassida, Chlamidodon, and Prorodon (XXVIII. 8, 65). The cylinder 

 of teeth was fm^ther stated to be wider in fi'ont, to be able to expand itself to 

 receive, and afterwards to contract on the engulfed particle of food, so as to 

 crush it and drive it inwards. 



To these notions of the natui-e and action of the organ in question, Stein 

 cannot assent. He states (p. 128) that he has frequently tried in vain to 

 isolate it. On killing an animalcule with solution of iodine, or with dilute 

 acetic acid, the funnel-like tube, at times straight, at others ciu^ved, is di- 

 stinctly displayed, as well in the smallest as in the larger specimens. It 

 tapers posteriorly, and ends abruptly by an open extremity in the ca\dty, 

 and is composed of the same resistant elastic membrane as the cuticle. 

 Stein gives it the name of the '•' oesophageal funnel." Its wider and thicker end 

 is truncate and dentate or serrate, having from 8 to 16 dentations : between 

 these the membrane appears to be plaited or groved for a considerable distance 

 do^vnwards ; and it is these plaits or folds which Ehrenberg took to be long 

 bristle-like teeth arranged side by side. This cylinder, therefore, is nothing 

 more than an involution of the integument. It can be retracted and appear 

 like a tapering oesophageal tube, or be protruded like a tinimpet- shaped pro- 

 cess beyond the general surface. It has not, however, that independent 

 motile power in itself represented by Ehrenberg ; but all its movements 

 depend upon those of the integument ; for Stein has never seen it either con- 

 tract or dilate, except simultaneously with the contractions of the general 

 surface. It bends, and is doubled up under pressure, and is neither denser 

 nor a more brittle tissue than the cuticle ; nor can it be resolved into rod-like 

 segments. 



The plaited upper portion is not apparent in all species which have a 

 homologous organ: thus mNassula ambigua (Stein, ]). 249) the infundibulum 

 is smooth, although the double outhne its membrane exhibits indicates its 

 very considerable thickness. 



Secretion. — Sufficient e\4dence of the operation of this function is found 

 in the Ciliated Protozoa, although no special organs or tissues can be pointed 

 out for its exercise, unless, indeed, the paii' of peculiar solid-looking organs 

 in the head of Opercidaria berberiformis, hereafter mentioned among accessory 

 undetermined structures, be considered glandular (XXX. 2 c). 



The production of cilia may be considered an act of secretion, exercised so 

 soon as an animalcule assumes a definite outline, and, imder certain circum- 

 stances in connexion with the encysting-process, repeated a second time 

 within the life-time of an individual. Again, the excretion thrown out 

 around Protozoa when about to encyst them^^elves is another example of the 



