of the Poly gastric Infusoria. 451 



him without reason. The analogy of this vesicle with the con- 

 tractile organ of the Rotifera, which appears from its evident 

 connexion with the ovary to be the seminal vesicle, is in favour 

 of this view. Wiegmann, in mentioning Ehrenberg's discovery 

 in his annual report*, remarked, that perhaps the contractile 

 vesicle might be a heart. He states, as his ground for this sup- 

 position, that it is always formed before the longitudinal and 

 transverse division of the body of the animal, which might ap- 

 pear to indicate that it was connected with some organ essentially 

 necessary to the vital process ; whilst, on the other hand, the or- 

 gans of propagation, which under other circumstances did not 

 commence their functions until the body was perfectly formed, 

 do not require so early a formation nor so constant an action. 

 However, it appears to me that Wiegmann's objection is weakened 

 on the one hand by the consideration that the division is always 

 an essentially distinct formation of the individual from that of 

 sexual reproduction, and hence that the laws of the development 

 of the two modes of formation of new individuals are by no 

 means identical ; on the other hand, by the supposition that at 

 every contraction seminal fluid is not evacuated. Siebold with 

 Wiegmann also considers the contractile vesicle as the first 

 form of a circulatory system and the first attempt at a cir- 

 culation of the nutritive fluid, but merely as a consequence of 

 the following presupposition : " Most probably the liquid fill- 

 ing the cavities which become distended by a kind of diastole 

 is a nutritious fluid emanating from the parenchyma, which at 

 the systole is again propelled into the parenchyma, whence the 

 necessary motion and distribution of this nutritive fluid are effected 

 and its stagnation prevented." As Siebold's view is based upon 

 this alone, and believing that I have removed Wiegmann' s objec- 

 tions, and Ehrenberg's view having at least one analogy, although 

 of itself not sufficient, I prefer the opinion of the latter ; but I 

 must not conceal the fact, that the occurrence of glands without 

 vesicles (in the Closterina and Bacillarina) appears to show that the 

 connexion of these two organs is not essential. Still it is not 

 impossible, that by the perfection of our optical resources the 

 contractile vesicle may be detected in these families also. 



Remark. — It would have been an important point to have also 

 taken the eyes (of both the Rotatoria and the Polygastrica) into 

 consideration ; however, as Schmidt in his paper on the Ro- 

 tatoria has likewise omitted this, it affords matter sufficient for a 

 distinct treatise. 



* Wiegmann's Arcbiv, 1831. 



2K2 



