1892.] 



MICROSCOPICAL JOURNAL. 



239 



inous cover, which is distinct from the body of tlie animal. In ad- 

 dition to this safeguard the creature further has attached to itself a 

 cover for the cup, which closes the opening when the body is re- 

 tracted. These various genera just mentioned form the order 

 CiLiATA, and we have now surveyed two classes and three orders 

 of Protozoa. 



Gregarina gigantea (figs. 13, 14, and 15). The Protozoa thus 

 far mentioned are none rf them true parasites, though many live 

 under circumstances which are biologically much the same. But 

 Gregarina lives as a true parasite in the body cavity of the earth 

 worm and other invertebrates. It is an elongate, protoplasmic 

 body with fixed outline but no cilia, flagella, or other locomotor 

 processes. There is a portion of the body at one end marked oft' 

 from the remainder by a slight constriction, but it is not a separate 

 organ. There is a single round nucleus. Gregarina reproduces 

 by spore formation (see fig. 15) as well as by division. 



Having now outlined a few of the genera of the Protozoa, our 

 second consideration is that of the group from the biological 

 standpoint. Do the various Protozoa among themselves as a 

 phylum permit us to understand them all as a genetic series, or 

 a series of animals related by ties of kinship? In order to survey 

 the phylum at a single glance I have prepared this table, in which 

 the lines of relationship ai"e indicated by reading across the page. 



Phylum. 



Order. 



f FORAMINIFEKA., 



f Rhizopoda . 



LOBOSA 



Genus. 

 f Spirolina. 



,' ROTALIA. 



"] Gromia. 



(^ LlEBERKUHNIA. 



f Hyalosphenia. 

 -! Difflugia. 

 1^ Amceba. 



Protozoa. 



■i SroROzoA , 



Heliozoa 



Radiolaria. 



Gregarina 



ctinosphehium. 

 lathrulina. 



[ Infusoria.. 



r Pyxicola. 

 r f, ...... I Vorticella. 



I LiLlATA < e 



j hXENTOR. 



! 1^ Paramecium. 



I f CdDOSIGA. 



[ FlAGELLATA <; NOCTILUCA. 



l^ Perioiniom. 



A glance at this table in connection with the facts already pre- 

 sented w^ill show that it is possible to conceive of the Protozoa as 

 a genetic series without doing violence to the facts ; in fact when 

 they are taken in connection with a full knowledge of the case, 

 of which only a very incomplete synopsis has been presented, no 

 other conception is rational. 



Let us suppose the case of an animal like amoeba under favor- 

 able conditions. We should expect it to grow and thrive abund- 

 antly but subject to competition by very force of numbers of its 

 own kind. With our present knowledge of biology we should 



