THE INFUSORIA. 89 



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

 appearance in its interior. Around tliis a clear layer is differ- 

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

 passes into the condition of the adult Gregarina gigantea. 



4. The Catallacta of Haeckel, represented by the genus 

 Magosphoera^ 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 JProtogenes and those of Prot- 

 aniceha. 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. 

 MagosjyJic^ra is thus very nearly an endoplastic repetition of 

 the moneran Protomonas — 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 Ixfusoeta. — Excluding from the miscellaneous as- 

 semblage of heterogeneous forms, which have passed under 

 this name, the Pesmidicp^ Piatomaccce^ Volvochiece, and 



V^ibrionidce, 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 — («) the so-called " ]\Ionads," or Pnfusoria 

 Jlagellata ; (b) the Acinetae^ or Pnfusoria tentacuUfera ^ and 

 (c) the Pnfusoria 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 



