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



If we consider a little more closely the nature of the circlet 

 of cilia which bears their food to the Vorticelhe, we find* that 

 it does not form a complete circle, but a spiral linef- This be- 

 gins in the vicinity of the orifice called the mouth by Stein (PI. 

 IX. figs. 1-3 c, d) a little to the right of it upon the ciliary disk 

 (fig. 1-5 h), runs above this orifice towards the left and round 

 the margin of the ciliary disk ; but before it again reaches its 

 starting-point, it descends upon the stem of the rotatory organ 

 into the commencement of the digestive apparatus. 



This commencement of the digestive apparatus (fig. \ c, d,e; 

 fig. 2 c, e; fig. 3 c, d, e,f, and fig. 4 c, e, f) cannot yet be re- 

 garded as the throat, or as a part of the oesoi)hagns (as Stein 

 has done), for the anus opens into it (at e) ; we will therefore, 

 by the recommendation of Professor J. Miiller, distinguish it by 

 the name of vestibulum from the other parts of the alimentary 

 apparatus. Ehrenberg figures this part too shallow, as a lateral 

 pit in which the mouth and aims are placed; whilst Stein only 

 distinguishes it from the true oesophagus in the Opercularice, in 

 which it is rendered remarkable by its width, but in most of the 

 Vorticellince regards it as the commencement of the oesophagus. 



The vestibulum continues the spiral line formed by the row of 

 cilia, constituting a bent tube, which contains a portion of this 

 spire of cilia. In accordance with the direction of this spiral, the 

 concavity of the tube is turned towards the right and its con- 

 vexity towards the left : on the convex side the lumen of the 

 tube is still more enlarged, especially in the parts ])laced furthest 

 inwards where the anus opens (at e). Between the anus and 

 the mouth which leads further inwards into the oesophagus 

 (figs. 3 & 4 e, /) springs a hent bristle (figs. 1-5 e, g), which is 

 generally long enough to project outwards beyond the peristome. 

 This bristle is stiff, and is only displaced a little to one side 

 occasionally, when balls of excrement which are too thick to 

 pass between it and the wall of the vestibulum are thrown out 

 from the anus, but it immediately returns again to its old 

 position. 



From the mouth a short tube, the (esophagus (figs. 3 & 4 e,f, h ; 

 fig. 5 h), with a far smaller lumen than the vestibulum, leads 

 to a rather wider fusiform portion (figs. 4 & 5 h, i), which we 

 will call the pharynx. In most Vorticellince (those with a con- 



* To facilitate the subsequent description, we must distinguish a dorsal 

 and ventral surface and an anterior and posterior part in the bodies of the 

 Vorticel/ce : we follow in this the mode of indication of Ehrenbcrj^, deno- 

 minating the attached part of the body the posterior, and the disk or rota- 

 tory ajjparatus the anterior, and characterizing that side of tiie bell which 

 is nearest to the mouth as the ventral side. 



t Ehrenberg represents this line as a spiral in some Voriicellce, but 

 generally reversed, whilst Stein describes it as a circle. 



