128 Mr. H, J. Carter on the Oi^ganhation of Infusoria. 



the lower or inner part of the organ, and at this point, therefore, 

 arc ])ushed inward as the vesieuhi becomes distended (tig. 68 n a). 

 Under the same circumstances, also, when the vesicula is slowly 

 dilating and contracting, it may be seen to be attached to a small 

 papilla on the surface, about twice the diameter of those which 

 surmount the trichocysts*, and through which it probably 

 empties itself (fig. 68 « «). In Otostoma there appears to be a 

 similar arrangement of vessels round each vesicula, and here also 

 they seemed to me to be branched, — at least such was my im- 

 pression after having watched this animalcule for a long time, 

 in order to determine the point. ^^ 



In Ammha and Aciinophrys the vesicula is generally single ; 

 sometimes there are two, and not unfrequently in larger Amosboi a 

 greater number. In Euglypha I have not been able to recognize 

 them, but mArcella vulgaris ?ind Difflugia proteiformis(^Q^. 79,80) 

 they may be seen in great number, situated round the margin of 

 that part of the animalcule which is within the test ; and from 

 their always reappearing, after contraction, in the same places 

 respectively, we may perhaps infer that the situation of the 

 vesicula in Amoeba and Actinophrys also is fixed, though from 

 their incessant polymorphism it appears to be continually vary- 

 ing in position. In Paramecium, and Ehrenberg's Enterodela 

 generally, the vesicula is either single or dual. When it exists 

 in great number in any of these (e. g. Chilodon cucullulus, 

 Ehr.), this appears to depend on accidental dilatations of the 

 sinuses in connexion with it. Thus, in the animalcule just 

 mentioned, where the vesicula is single, and seems to be sub- 

 terminal and lateral in its normal position, it is not uncommon 

 to meet with a group in which every member presents a variable 

 number of contracting vesicles, variably also and irregularly di- 

 spersed throughout the body, without one being in the true posi- 

 tion of the vesicula (figs. 82, 83). That the vesicula does make 

 its appearance now and then may be inferred, as it perhaps may 

 also be inferred that from over-irritability, or some such cause, 

 it does not remain under dilatation long enough to receive the 

 contents of the sinuses ; and hence their accidental dilatation, 



* These are narrow, fusiform cells, arranged perpendicularly, and at 

 some little distance from each other, under the pellicula, where they thus 

 form a layer all over the body, and each, according to Dr. Allman, contains 

 a delicate, resilient thread, coiled up in its interior, which, just after the 

 cells have been forcibly pressed out into the water, by crushing the ani- 

 malcule, causes them to assume, for a second, a circular form, and then 

 burst, through which the thread is set free, and, lying rigid on the glass, 

 presents the form of an acicular crystal, terminated at each end by a 

 pointed extremity, one of which, being more attenuated than the other, 

 appears like an appendage. To these cells Dr. Allman has given the name 

 of "trichocysts " (Quart. Journ. Microscop. Sc. vol. iii. p. 177, 1855.) 



