INFUSORIA. 



[ 415 ] 



INFUSORIA. 



the principal locomotive and ingestive or- 

 gans. The diversity of shape and structure 

 is very great amongst the Infusoria ; and it 

 is therefore necessary to consider the details 

 of the different parts composing them sepa- 

 rately and in order. 



Intcf/ument. The bodies of Infusoria con- 

 sist of sarcode, of which the outer layer 

 possesses usually considerably more consist- 

 ence than the internal portion. Cohn de- 

 monstrated the presence of this pellicular 

 layer in Paramecium by the addition of 

 alcohol, and noticed that the softer tissues 

 remained united to it by a process in one 

 place only, where the short gullet, which is 

 also lined by a continuation of the external 

 tissue, dips down and merges into them. 

 This hard transparent pellicle or cuticle is 

 elastic, but its contractili ty is doubted ; and 

 it often becomes visible when the Infusoria 

 are kept in a small quantity of water upon 

 a slide, the globules of sarcode which escape 

 from rupture of the body carrying it before 

 them. It is frequently beautifully marked 

 with minute depressions (PI. 32. fig. 1), re- 

 gularly arranged, and from each of which a 

 cilium arises. This cuticle must be regarded 

 as a secretion from the outer or cortical 

 layer of the sarcode ; and it is by no means 

 improbable that Leydig's assertion that it 

 arises from a layer of extremely delicate 

 and small cells will turn out to be correct. 



Many Infusoria have a carapace or lorica, 

 which is in some soft and in others very hard ; 

 the relation of the hard carapace to the pelli- 

 cular layer is not, however, very distinctly 

 known. The carapace is often not adherent to 

 the body of the Infusoria, but forms a kind of 

 sheath for the protection of the soft tissues ; 

 or it may form one or two valves which are 

 more or less completely soldered together. 

 These tests are thicker and less elastic than 

 the cuticle ; and the peduncles which sup- 

 port many species of Infusoria, and which 

 in some instances are hollow and contain a 

 contractile sarcode by which they are 

 secreted, belong to the same kind of struc- 

 tures. Beneath the pellicular layer, the 

 substance of the body frequently appears 

 thicker, although no distinct layer can be 

 separated; and it is doubtful whether the 

 markings are situated in the outer coat, or 

 whether the latter derives them from being 

 moulded upon the inner coat, to which 

 they may properly belong. 



This cortical layer (parenchyma of Cla- 

 parede and Lachmann), as it is called, is 

 firmer than the central and more diffluent 



sarcode, with which it is continuous inter- 

 nally. It is almost homogeneous ; but an 

 indefinite and irregular reticulation and 

 fibrillation may be observed in many species, 

 and especially in the Vorticellae, close to 

 the insertion of the peduncle, with whose 

 contractile fibre it is continuous. The 

 fibrils and the so-called muscles of the 

 peduncle are composed of sarcode, which 

 has no definite structure, and which is here 

 and there faintly granular ; but they possess 

 the power of contracting more or less. 

 Besides these, there are the minute gra- 

 nule-looking cells immediately under the 

 pellicle (which have already been noticed), 

 the contractile vesicles or spaces with their 

 ramifications, the nucleus and nucleolus, 

 and sometimes chlorophyll-granules. When 

 present, the brightly coloured pigment- 

 spots, the so-called eyes, appear to be pro- 

 duced in this layer ; and the whole of the 

 cilia are continuations of it. Wright has 

 observed amoeboid movements in this layer. 

 The portion of the body which is surrounded 

 by and more or less continuous with the cor- 

 tical layer, and which is subject to rotation, 

 is softer and often contains granules and 

 corpuscles resembling fat-cells. The mouth 

 and gullet open into this central sarcode; 

 and the anus, when it exists, leads from 

 it. Numerous digestive vacuoles are ob- 

 served in this watery sarcode, which often 

 presents the appearance of being faintly di- 

 vided by films and fibres of less diffluent 

 protoplasm. 



The existence of the outermost coat or 

 pellicle is demonstrated by the phenomenon 

 of ecdysis, which occurs in certain species. 

 But this does not exist in all cases ; for in 

 some Infusoria the body adheres readily to 

 the glass of the slide on which it is viewed 

 under the microscope, and is torn up into 

 fragments in the endeavour to free itself. 



The cortical layer of some species pro- 

 duces trichocysts or thread- cells. These 

 are fusiform, colourless, and transparent 

 bodies, 1-2500" in length, arranged on the 

 outside of the body and perpendicularly 

 to it. Irritation of the surface causes them 

 to be transformed into long filaments ; and 

 they are more or less like the thread-cells 

 of the Polypes; but they are developed 

 within the cortical layer, and not as cells on 

 its surface. 



Minute amylaceous crystalloids, coloured 

 blue with iodine, have been observed in 

 Strombidium. 



Locomotive organs. No distinct muscular 



