316 GENERAL HISTORY OE THE INFIISORIA. 



suiToimding and communicating dii-ectly \Yith them. These accessory vesicles, 

 he tells us {op. cit. p. 130), are, " under exhaustion of the animalcule from 

 various causes, so distended, and thus so approximated, as to assume the 

 appearance of an areolar structure immediately in contact with the vesicula. 

 Each globular sinus would, however, appear to be the proximal or largest of 

 a concatenation of smaller ones, which diminish in size with their distance 

 from the vesicula." This account tallies with that recorded by Mr. Samuelson 

 (J. M. S. 1857, p. 104), respecting the single globular vesicle of Glaucoma 

 scintillans, which ^' when it contracts forces the fluid into others which 

 appear temporarily formed around it ; " and these, by contracting in their turn, 

 refill the central vesicle. 



Besides the seemingly simple spherical vesicles, there are others that pre- 

 sent evident branches and a different figure. Such, for instance, are the 

 elongated vascular canal of Spirostomum, and the annular canal with its row 

 of vesicles down the side, — which seem capable of coalescing into a continuous 

 channel, seen in Stentor (XXIX. 7). In Paramecium Aurelia (XXV. 329), 

 each contractile vesicle assumes a stellate form, owing to the radiating pro- 

 cesses it sends off on all sides, and which Eckhard represented as prolonged 

 through the body by interrupted channels. It is from the study of this 

 Paramecium especially, that observers have generally arrived at the belief in 

 the existence of vascular canals in the Cihata, connected with the contractile 

 vesicle as a central organ. That there exists a vascular system more or less 

 distributed through the body, most recent microscopists are in accord : we 

 may mention Lieberkiihn, Lachmann, Mr. Carter, Professor Busk, and Mr. 

 Samuelson. 



As this apparatus ^vill be best considered in connexion with its assigned 

 functions, we shall speak of them together, premising oui' account with the 

 history of Ehrenberg's conjectures on the nature and function of the con- 

 tractile vesicle. This distinguished naturahst was led by his hypothesis of 

 organization to seek for each of the organs of higher animals a parallel or 

 analogue in the Infusoria ; and one of the most curious analogies he hit upon 

 was that of the contractile sac with the spermatic vesicle. In this office he 

 represented the vesicle as receiving from the testis (nucleus) a reproductive 

 fluid, which it again ejected among the ova (granules, alimentary vesicles, 

 &c.) occupying the interior of the animalcule. In this peculiar notion 

 Ehrenberg has met with few disciples : for, as Siebold has justly objected, it 

 is a perfectly gratuitous hypothesis, without analogy in the animal kingdom ; 

 for in no animal is such a thing seen as an incessant projection of seminal 

 fluid into the interior ; and further, both the nature of the nucleus as a testis 

 or secretory organ of spermatic fluid, and the existence of recipient ova, are 

 at best very doubtful hypotheses. 



The opinions now in vogue concerning the function of the contractile 

 vesicle and of its prolongations or processes are that it is either (1) a water- 

 vascular and respiratory system, homologous with that of the Rotatoria, 

 or (2) homologous with a blood-vascular system, or (3) an excretory appa- 

 ratus. The first conjecture presupposes a direct commimication between the 

 fluid in this vascular system and the surrounding aqueous medium ; by the 

 second, no such direct communication need be presumed ; the third view is 

 especially supported by Mr. Carter, Bergmann, and Leuckhart. 



In his notions concerning the organization and function of the contractile 

 vesicle. Stein differs from most other recent investigators. As we have 

 already seen, he denies a limiting membrane to the vesicle ; he, moreover, 

 can neither acquiesce in the belief of the existence of outlets, nor in the 

 respiratory piu'posc attributed to it by Siebold and 0. Schmidt. He is even 



