474 CLASS II. CILIA TA. 



a rudimentary alimentary tract. The rod-like bodies known as trichocysts, 

 recorded in but one or two doubtful instances as yet in connection with the 

 Flagellata (Chilomonas and Merotrichd), represent a common elementary factor of 

 the cortical layer of the Holotrichous Ciliata, and are next met with in the Metazoic 

 section of the Turbellaria. Already, in the cases of Anisonema grande and Entosiphon 

 sulcatus, attention has been directed to the exceptional composite rosette-shaped 

 contour of the contractile vesicle. Among the Ciliata this organ often exhibits a yet 

 higher degree of differentiation, not unfrequently (Spirostomum, Stentor, Ophrydiurti) 

 being produced peripherally into one or more extensive canal-like prolongations, 

 and may undoubtedly be accepted as foreshadowing the more or less complex 

 water-vascular, segmental, and ambulacral systems of the Metazoic classes of the 

 Turbellaria, Trematoda, Rotifera, higher Annelida, and Echinodermata. An im- 

 portant advance in the organization and physiology of the Infusoria Ciliata has 

 to be recorded in connection with all matters pertaining to the phenomena of 

 reproduction. Multiplication by longitudinal or transverse fission is, as among 

 the Flagellata. a common form of propagation. The encystment and breaking up of 

 the entire body-mass into sporular elements characteristic of the majority of the 

 Flagellata, and in which form of reproduction they exhibit decided vegetable 

 affinities, is of very rare occurrence among the Ciliata, the several Holotrichous 

 genera Colpoda, Otostoma, and Ichthyophthirius constituting the chief exceptions. In 

 place of this, new zooids with the Ciliata are usually produced by the subdivision 

 of the nucleus or endoplast into germinal elements, which are liberated independently 

 from the parent animal after the manner of the ova or embryos of the Metazoa. A 

 first progress in this direction has nevertheless been recorded of certain of the higher 

 Eustomatous Flagellata. The phenomenon of genetic union, or conjugation, directly 

 or indirectly associated with the reproductive faculties, exhibits likewise, among the 

 Ciliata, a decidedly advanced formula. While with the Flagellata, so far as is known, 

 the conjugative process is complete and permanent, according with the genetic 

 union or so-called zygosis of unicellular plants, this process, though similarly mani- 

 fested among certain Ciliata, such as the Vorticellidae, is more usually replaced by 

 an incomplete and transient conjugative act that corresponds more nearly with the 

 copulation of higher animals. Finally, while all Flagellata are essentially unicellular, 

 possessing but a single, and in almost all instances very simple, nucleus or endoplast, 

 among the Ciliata this structural element very commonly exhibits a highly com- 

 plex type of composition, and being in many instances represented in plurality, 

 demonstrates the further advance made by these organisms towards the condition 

 of multicellular beings. 



The character and mode of distribution of the cilia yield reliable data for the 

 subdivision of this class into minor sections or orders, the following plan as here 

 adopted being in accordance with the one first introduced by Professor Stein in 

 the year 1857. While the more characteristic members of these several orders 

 yield features which permit of their natural and readily appreciated distinction, 

 intermediate forms occur in each such group indicative of their close relationship 

 and common design. Special reference is made to the more prominent of these 

 annectant or transitional types in the general description of the respective orders. 



SYNOPSIS OF THE ORDERS OF THE INFUSORIA CILIATA. 



Cilia distributed over the entire surface of the } 



body, similar, or differing but slightly in > Order I HOLOTRICHA. 



character. 



Cilia distributed over the entire cuticular sur- 1 



face; the oral series of conspicuously larger > ,, II HETEROTRICHA. 



size. 



Cilia not universally distributed, mostly limited 

 to a conspicuous circular or spiral adoral 

 wreath. 



Locomotive cilia, confined to the inferior or 



IIL .. PERITRICHA. 



ventral surface of the body. / IV HYPOTRICHA. 



