314 GENEEAL HISTORY OF THE INEUSOEIA, 



of the body, the appearance at times of additional vesicles, and consequently 

 also the discrepancies of authors as to the numbers present, are exphcable 

 by supposing the accidental dilatation of a tube here and there — as a vari- 

 cose vessel, — the dilatations representing for the time additional contractile 

 spaces. 



This explanation occuiTed, among others, to Mr. Carter. Thus he remarks 

 (A. N. H. 1856, xviii. p. 128) that in Chilodon, where the vesicle is normally 

 single and near one extremity, it is not imcommon to meet, amid a group of 

 these animalcules, various indi\T[duals presenting a variable number of con- 

 tractile vesicles irregularly dispersed through the body, without one being m 

 the true position of the ' vesicula.' " That," he writes, " the ' vesicula ' does 

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

 be inferred that from over-irritabihty, or some such cause, it does not remain 

 under dilatation long enough to receive the contents of the sinuses ; and hence 

 their accidental dilatation, and the appearance of a plurahty of vesiculae." 



To this accidental dilatation of vasculai^ channels at particular points may 

 be referred the 50 to 60 regularly placed vesicles described by Gegenbauer 

 in Trachelius, the 12 to 16 mentioned by Siebold and Perty in Ampliileptus, 

 and also the row of them seen along the side of Stentor. In this last-named 

 genus there is a circular canal sm-rounding the head or ciliary wreath, which 

 sends off a branch at right angles along the side to nearly its posterior end 

 (XXIX. 7). In Sjpirostomum, again, a long contractile channel occuj)ies the 

 length of the body. 



The existence of a second vesicle in an animalcule normally possessing but 

 one, Ehrenberg explained by supposing an act of fission to have occurred 

 prior to division of the entire being, — an explanation in which Mr. Carter 

 concurs. But if Stein be right, the contractile vesicle does not undergo 

 fission, but makes its appearance in the newly-formed half by an act of 

 development de novo. In this statement Wiegmann concurs (Perty, p. 63). 



Ehrenberg concluded the contractile spaces to be true sacs, limited by a 

 definite membrane, — a conclusion sanctioned also by Siebold, forasmuch as, 

 during successive contractions and dilatations, the vesicles retain the same 

 place, figure, and number. Mr. Carter supphes direct evidence of the fact 

 {A. N. H. 1856, xviii. p. 130), having obsei-ved on one occasion a vesicle re- 

 main pendent in a globular form to the buccal cavity of a Vorticella, '' when, 

 by the decomposition of the sarcode and the evolution of a swarm of rapidly- 

 moving monadic particles, these two organs, with the cylindrical nucleus or 

 gland, though still slightly adhering to each other, were so dissected out as 

 to be nearly separate ; and thus yielding in position from time to time, as they 

 were struck by the little particles, their fonns and relative positions respect- 

 ively became particularly e\ident." Moreover, Lachmann {A. N. H. 1857, 

 xix. p. ''Z^Q) argues at length in favour of the true vesicular character of 

 contractile spaces. Thus he remarks — " The mode of contraction, which 

 differs from the other contractile phenomena of _the parenchyma of the body, 

 appears to speak decidedly in favour of the vesicular nature of the contractile 

 space. The circumstance that, before its complete expansion, it frequently 

 appears to be di\ided into two or three, is not opposed to this, as a vesicle 

 may very weU be constricted into two or more parts by the partial contrac- 

 tion of annular portions, or by strictures. Some other facts appear to be ia 

 favour of the vesicular nature of the contractile space, such as the phaenomenon 

 presented by Spirostomum amhiguum, already referred to, in which balls of 

 excrement pass to the anus between the contractile space and the outer skin 

 of the animal, and, although often arching the waU of the contractile space 

 into a semiglobular form, yet never break through into it. In Actinoj)hrys, the 



