32 A MANUAL OF THE INFUSORIA. 



aperture, definite or distributed, the zooid absorbing through the surface of 

 its integument the nutritious liquid pabulum in which it is constantly 

 immersed. In their development the Protozoa exhibit a tendency to increase 

 chiefly by the process of binary subdivision or gemmation, or through 

 the breaking up of the entire body into a number of sporular elements, 

 which may or may not be preceded by the conjugation or zygosis of two 

 or more individual zooids or units. No sexual elements developed sepa- 

 rately, and corresponding with the ova or spermatozoa of higher animals, 

 occur among the Protozoa, and in no case is there associated with the 

 developmental phenomena of this sub-kingdom the formation of a multi- 

 cellular germinal layer or blastoderm, the fundamental origin and ground- 

 work of all tissue structures in the more highly organized animal groups 

 or Metazoa. 



The earliest subdivision of the Protozoa into secondary sections or 

 orders as initiated by Von Siebold partook, as related in the preceding 

 chapter, of the simplest possible character. All the types then known were 

 separated by this author into the two subordinate groups of the Rhizopoda 

 and Infusoria, the former characterized by the pseudopodous, and the 

 latter by the ciliate or flagelliform character of the locomotive append- 

 ages. Correlated with the systems of the present day, this proposed 

 primary subdivision of the Protozoa still finds many advocates, an identical 

 plan, though in different wording, being indeed adopted by Professor 

 Huxley in his 'Anatomy of Invertebrated Animals,' 1878, p. yd, and in 

 which it is suggested that all Protozoa may be conveniently distinguished 

 as Myxopods and Mastigopods. These two correspond so precisely and 

 respectively, with reference to their locomotive appendages, with the Rhizo- 

 poda and Infusoria as instituted by Von Siebold, that but little advantage is 

 to be gained apparently by the proposed exchange. With reference to the 

 latter of these two terms, it is further worthy of remark that it coincides to 

 a considerable extent, in both sound and the sense implied, with the 

 Mastigophora of R. M. Diesing. 



Following out the further subdivision of the two foregoing primary 

 sections of the Protozoa into secondary groups or orders which has up to 

 the present time found most extensive support, the first — that of the 

 Rhizopoda, or Myxopoda — is found to include the Amcebina, Foraminifera, 

 and Radiolaria, while the second — that of the Infusoria, or Mastigopoda — 

 embraces in a similar manner, and in accordance more especially with the 

 classification-scheme introduced byMessrs. Claparede and Lachmann,the four 

 orders of the Ciliata, Cilio-Flagellata, Flagellata, and Suctoria. For this last 

 group — that of the Suctoria — Professor Huxley has proposed to substitute 

 the very appropriate title of the Tentaculifera, recent investigation having 

 shown that the more customary suctorial organs may be replaced by simply 

 prehensile and non-suctorial tentacles. By some, the small endoparasitic 

 group of the Grcgarinidae is reckoned to constitute a third and distinct class 

 of the Protozoa, but it is evident that wc have here a degraded group of the 



