THE INFUSORIA. 89 



passes into a quiescent state, and the " nucleolus " makes its 

 appearance in its interior. Around this a clear layer is diifer- 

 entiated, giving rise to the " nucleus," and the pseudo-Hlaria 

 passes into the condition of the adult Gregarma fjigantea. 



4. The Catalla-Cta of Haeckel, represented by the genus 

 3fagosphfjEra, are, in one stage, myxopcds with long pseudo- 

 podia, which, broad and lobe-like at the base, break up into 

 fine filaments at their ends, and may therefore be said to be 

 intermediate between those of Protogenes and those of Prot- 

 anioeba. The myxopod is provided with a distinct endoplast 

 and a well-marked contractile space. When fully fed, it se- 

 cretes a cyst and divides into a number of masses, each of 

 which is converted into a conical body, with its base turned 

 outward and its apex inward. These conical bodies are im- 

 bedded in gelatinous matter, and thus cohere into a ball, from 

 the centre of which they radiate. Each develops cilia around 

 its base, and contains an endoplast and a contractile vacuole. 

 After the complex globe thus formed has burst its envelope, 

 it swims about for a while, like a Volvox. The several cilia- 

 ted animalcules feed by taking in solid particles through the 

 disk. They then separate, and, finally, retracting their cilia, 

 become myxopods such as those with which the series started. 

 Magos2)h(jera is thus very nearly an endoplastic repetition of 

 the moneran Protonionas — the mastigopod being provided 

 with many small cilia, instead of with a couple of large fla- 

 gella. On the other hand, the Catallacta are closely allied 

 to the next group, and, I am disposed to think, might well be 

 included in it. 



5. The Infusoria. — Excluding from the miscellaneous as- 

 semblage of heterogeneous forms, which have passed under 

 this name, the Desmidiw^ Piatomaccm^ Volvocinece, and 



Vibrionidce, which are true plants, on the one hand ; and the 

 comparatively highly-organized Potifera, on the other ; there 

 remain three assemblages of minute organisms, which may be 

 conveniently comprehended under the general title of Infu- 

 soria. These are — (a) the so-called " Monads," or Infusoria 

 flagellata ; (b) the Acinetce, or Infusoria tentaculifera ; and 

 (c) the Infusoria ciliata. 



(a.) The Flagellata. — These are characterized by pos- 

 sessing only one or two long, whip-like cilia, sometimes (when 

 more than one are present) situated at the same end of the 

 body, sometimes far apart. The body very generally exhib- 

 its an endoplast and a contractile vacuole. There is no per- 

 manently open oral aperture, but there is an oral region, into 



