Dr. C. F. J. Lachmann on the Organization of Infusoria. 229 



detected, in various Vorticellina, in which Ehrenberg states that 

 he saw muscular strise at the posterior extremity. It forms a 

 hollow cone, the apex of which is situated in the hinder extre- 

 mity of the animal, and, in the contractile-stemmed species, is 

 produced into the muscle of the stem; in its apparent section it 

 of course appears like two small fibres separating from each 

 other like a fork, as which, indeed, it has hitherto been always 

 regarded, except by Ehrenberg*. This layer is very beautifully 

 seen in Epistylis plicatilis, in which we may most completely 

 convince ourselves that it is a special stratum, which possesses 

 contractility. In Epistylis plicatilis, namely, during the con- 

 traction of this stratum, the non-contractile part of the paren- 

 chyma which surrounds it, with the skin covering it, separates 

 from the contractile layer, and forms the well-known folds, 

 whilst the contractile or muscular layer becomes shortened and 

 thickened without folding. The structure of the contractile 

 stem is carefully treated of by Stein f and especially by Czer- 

 mak Xi to whose statements I may refer. As the sole function 

 of the innermost part of this stem appears to be contraction, 

 and it is not perfectly structureless, I think we need not hesitate 

 in calling it a stem-muscle ; and I cannot allow any value to 

 Stein's objection, namely, that it still contracts even when the 

 stem is not attached to another object, for the muscle does not 

 thus lose its insertion, as it is attached to the sheath of the stem 

 itself by its hinder extremity, and not to the foreign object. 

 Perhaps the transverse annulations which are exhibited by the 

 bodies of some Vorticellina, are to be attributed to muscular 

 fibres ; at all events, they do not belong to the skin, but to the 

 parenchyma of the body. 



After we have thus mentioned what has been ascertained up 

 to this time with regard to organs unconnected with reproduc- 

 tion in the Infusoria, nothing remains to be considered except 

 the mode of propagation. 



Without entering into a controversy upon the generatio cequi- 

 voca, which now, fortunately for science, is almost solely de- 

 fended by men§ whose observations are so superficial, that no 

 criticism of them is necessary, we may pass at once to the true 



* Stein asserts that this does not occur in all contractile-stemmed Vor- 

 ticellincB ; I have always succeeded in seeing it, even in the Vorticella mi- 

 crostoma and Zoothamnium affine, St., which Stein represents without it. 



t Log. cit. p. 78. 



X Siebold and Kolhker's Zeitschr. iv. p. 438. I cannot confirm Czer- 

 mak's statement, that the stem of the VorticellincB is sometimes twisted to 

 the right and sometimes to the left, as I have always found it twisted in 

 the same direction as the spiral of cilia, in a great number of cases in which 

 I examined it carefully with this view. 



§ Pineau, Dr. Gros, &c. 



