of the Poly gastric Infusoria. 445 



very rarely, and only when the animals were dying. Even if 

 Siebold has seen it frequently and always in living specimens, 

 which I however doubt, still he cannot conclude from this, that 

 these spaces are not inclosed by any membranes ; might they not 

 be rent by the mutual pressure of the tilled gastric cells on ac- 

 count of their delicate structure ? 



I shall conclude the considerations of the alimentary canal 

 with an observation which appears to me especially adapted for dis- 

 proving Siebold' s views; it is this: Ehrenberg discovered that when 

 carmine and indigo are mixed with water containing Paramecium 

 Aurelia, in a short time some of the cells of the animalcule are 

 occasionally filled with the red colouring matter only, others with 

 blue. I have also seen this ; it was first shown me by my teacher 

 himself, and I have several times subsequently observed it. 

 Siebold's mechanical explanation, in my opinion, is not sufficient 

 to account for it ; it constitutes a phenomenon which presup- 

 poses a tolerable development of the sense of taste. 



Remark 1. — At p. 16 in note 1, Siebold says: "That organ 

 which occurs in Trachelius Ovum and is regarded by Ehrenberg as a 

 branched intestinal canal, has always appeared to me to be a fibrous, 

 certainly not hollow cord, which runs through the extremely loose 

 parenchyma, giving the interior of the animal a coarsely reticu- 

 lated aspect by its ramifications." I have hitherto seen this ani- 

 malcule twice only, as it is rare, and I cannot therefore form any 

 definite opinion upon this organ. But I may assert with cer- 

 tainty that Siebold has either never seen it in a natural state, or 

 has entirely mistaken its structure ; for it requires a mere glance 

 through the microscope to be convinced, that the question of its 

 being a fibrous organ cannot be entertained for a moment. 



Remark 2. — If Siebold denies the existence of an intestine in 

 the Poly gastric Infusoria, I am not aware how he can correctly 

 denominate the excretory spot the anus, and why the excrements 

 cannot exude from every part of the body. 



Propagation. 



6. The organs by which the preservation of the species is 

 effected have always had a peculiar interest with physiologists, 

 and have hence been treated of with a particular satisfaction* 

 The delicacy of the parts and the mystery of the sexual process 

 have a special charm with investigators, which is still more in- 

 creased in the Infusoria by the minuteness of their forms. I 

 shall therefore enter fully upon this point. If we first ask our- 

 selves — how the Polygastrica are propagated ? — it must be an- 

 swered : 



1) Viviparously . — Ehrenberg first observed this in Monas vi- 

 vipara, in which the phenomenon is common. Moreover a some- 



