( 8oi ) 



CHAPTER IX. 



SYSTEMATIC DESCRIPTION OF THE INFUSORIA-TENTACULIFERA. 



Class in, TENTACULIFERA, Huxley. 



Animalcules bearing neither flagellate appendages nor cilia in their adult 

 state, but seizing their food and effecting locomotion, when unattached, 

 through the medium of tentacle-like processes developed from the cuticular 

 surface or internal parenchyma ; these tentacles simply adhesive, or tubular 

 and provided at their distal extremity with a cup-like sucking-disc ; an 

 endoplast and one or more contractile vesicles usually conspicuously 

 developed; trichocysts rarely, if ever, present ; increasing by longitudinal or 

 transverse fission or by external or internal bud-formation. Inhabiting salt 

 and fresh water. 



The Tentaculiferous Section of the Infusoria, comprising Acineta and its allies, 

 while including, in comparison with the classes of the Flagellata and Ciliata already 

 described, a relatively small number of generic and specific forms, invites, with 

 reference to the remarkable structural and developmental features of its members, 

 an equal or even greater share of the biologist's attention. Although, as previously 

 shown,* the Tentaculifera, during their norriial adult phase of existence, betray no sign 

 of affinities with either of these preceding classes, they are in their embr)'onic 

 condition more or less completely clothed with vibratile cilia, and may also, under 

 certain conditions (see Podophrya fixa) temporarily develop cilia in ])lace of their 

 tentacula. It may be hence logically predicated that this class of the Infusoria is an 

 offshoot from the Ciliata, and that it consequently occupies a relatively higher position 

 in the zoological scale than do the members of the last-named class. Supplementary 

 evidence is afforded in this direction in connection with the fact that the ciliation of 

 the embryos of the Tentaculifera conforms roughly among the various species and 

 genera with that of the three more important groups of the Ciliata distinguished by 

 the titles of the Holotricha, Pcritriclia, and Hypotricha ; the cilia in Hke manner 

 being in one series developed upon the entire cuticular surface, in a second being 

 restricted to an anterior tuft or annular girdle, while in a third the cilia are developed 

 exclusively on the ventral surface of the body. It is further worthy of remark that 

 the holotrichously ciliated embryos are derived from the simplest Tentaculifera, 

 such as Podophrya, while the hypotrichous embryos are the more exclusive produce 

 of such higher types as Dendrocometes and Ophryodendron. 



The recognition of the Tentaculifera as a distinct class or order of the Infusoria 

 has been accomplished at a comparatively recent date. By Ehrenberg, as shown m 

 his Classificatory System, Vol. I. p. 201, they were referred together with the Diatoms 

 and Desmids to the group of the Bacillaria, while Perty included them with 

 Actinophrys in his group of the Actinojjhrina. Stein for many years advocated the 

 opinion that its members represented developmental phases only of various 



• See Vol. I. 1). 107 cl seq. 

 VOL. II. 



