41 GENERAL HISTOEY OF 



From the preceding conflicting opinions and observations, no satis- 

 factory deduction can be made ; Ehrenberg's opinions, however, are 

 entitled to great respect, although the theory of a polygastric structure 

 may not admit of demonstration. 



The annoimcement of Ehrenberg of the discovery of a dental 

 apparatus, must find place in this section. This apparatus occui's in 

 the foiin of a cylinder of long bristly teeth, placed behind the oval 

 aperture, and is readily seen in Ckihdon, Nccssula, Chlamidodon, and 

 Prorodon teres. See fig. 283. 



Section XIV. — Of the Vascular and Respiratory Systems, and of 

 the Secretions of Polygastrica. — In no creature of this class can a 

 vascular system be satisfactorily demonstrated : — that thought to 

 have been such in Paramecium aurelia, was merely clusters of ova. 



The above statement follows from the researches of Ehrenberg ; 

 but Siebold, "Wiegmami, and others, would trace the first outHne of 

 a circulatory apparatus in the existence of the conti'actile vesicle, 

 found in all those with evident mouths f StomatodaJ, as well as in a 

 few without such orifice (Astoma), as mentioned in the section on 

 the reproduction of Polygastrica. Ehrenberg assigned a very different 

 purpose to the contractile vesicles, regarding them as spermatic sacs, 

 the nucleus being the secreting testis. 



The Berlin natui'alist mainly based this h}-[)othesis on the simi- 

 larity of the contractile vesicles to those in Rotatoria, which he 

 frilly believed to foi-m a part of the male generative apparatus. But 

 since modern researches have overtmiicd the supposition of the 

 monoecious natiu^e of Rotiferce, and the exposition, consequently, of 

 their generative apparatus, as given by Ehrenberg, all analogies 

 resting on the latter, fall to the groimd. Indeed, the argument from 

 analogy would now be the other way ; for as such vesicles in the 

 Rotatoria have no generative character, it might be assumed that 

 their analogies in the Polygastrica, are alike devoid of it. 



The contractile vesicles in question, appear like clear hollow spaces 

 in the parenchyma of the Infusoi'ia, the contraction (systole) of 

 which, according to Ehi-enberg and his pupil Eckhard, (Wiegmann's 

 Arcliives, 1846, and Annals Nat. Hist. vol. xviii. p. 433), may be 

 regular or iiTcgular, but is defined by Siebold as rhj-thmical. 



In most genera, but one vesicle exists, in others two, and in a few 



