OF THE PROTOZOA. CILIATA. 301 



actual homogeneity of tissue. The act of differentiation is carried so far that 

 certain distinct organs and parts become distinguishable. Thus there is a 

 mouth or oral orifice for the entrance of food, succeeded by a dilated cavity — 

 an oesophagus or pharj-nx, which is contracted posteriorly into a tubular 

 prolongation of various length, homologous with a digestive or alimentary 

 tube. Apart from this rudimentary alimentaiy apparatus, numerous globular 

 or vesicular spaces containing granular particles or objects evidently swallowed, 

 are met with in the general loose contents of the body ; these were the di- 

 gestive sacs, or stomach-vesicles, so much insisted upon by Ehrenberg ; other 

 included organs are the contractile vesicle, a certain striated cylindrical organ 

 in one or two genera described by Ehrenberg as a dental cylinder or teeth, 

 the nucleus with usually its nucleolus, the red speck (eye) in Opliryoglena, 

 and in one genus a pair of organs imagined by Stein to be glandular. To 

 these contents Carter adds spermatozoida, and Perty internal germs or ovules. 



We have abeadj^ mentioned chlorophyll-corpuscles in some genera, and 

 the general prevalence of fat-vesicles and granules interspersed within the 

 substance of the body, or collected into a layer as in several of the Vorti- 

 ceUinci ; the collection of fat- corpuscles is remarkable in the contracted portion 

 or base above the point of attachment, whether this be by a pedicle or not. 

 " Perhaps," he adds, " the transverse annulations which are exhibited by the 

 bodies of some VortkelUna are to be attributed to muscular fibres ; at all 

 events they do not belong to the skin, but to the parenchyma {i. e. the cor- 

 tical lamina) of the body." 



Lately, Lachmann has broached the hypothesis that an actual muscular stra- 

 tum lies within the cortical layer. He wiites {A. N. H. 1 857, xix. p. 228) — '' I 

 was so fortimate, in common with my friend Claparede, as to observe an indu- 

 bitable separate contractile layer, in which longitudinal striae were generally 

 to be detected in various Vorticellina, in which Ehrenberg states that he saw 

 muscular striae at the posterior extremity. It forms a hollow cone, the apex of 

 which is situated in the hinder extremity of the animal, and, in the contrac- 

 tile-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 plicaiilis, in 

 which we may most completely convince ourselves that it is a special stratum, 

 which possesses contractility. In Epistylis plicatilis, namely, duiing the con- 

 traction of this stratum, the non-contractile part of the parenchyma 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 be- 

 comes shortened and thickened without folding." 



Organs of Digestion, Nutrition, and Secretion. — To take the several parts 

 or organs in succession, we will first consider those concerned in the processes 

 of digestion and nutrition, beginning with the oral orifice or mouth. This is 

 variously situated in different Ciliata, its position having reference to the figiu'e 

 and the mode of life, and being generally indicated by the particular provi- 

 sion made to secure a proper ciuTcnt of water into it, such as a tuft, a curved 

 row, or a circlet of larger cilia, a process or a depression of the body, the axis 

 of a convolution of the surface, and the like. Thus in Lacrymana, Enchelys, 

 Prorodon, Cohps, &c., it is at the anterior narrower extremity ; in Trachelius 

 and AmpTiileptus it has a similar position, but is besides under cover of a 

 process of the body. In Chilodon a still larger segment surmounts it ; in 

 Nassida, Paramecium (XXIX. 28), and in Pleuronema (Duj.) it is lateral; 

 and lastly, among the Vorticellina it is within an involution of the integu- 

 ment of the head, called the ' vestibulum,' on one side of the cUiated disk 



