THE INFUSORIA 419 



secretion by the pellicle of the inferior surface of the body, and it 

 is never contractile. In many forms it expands distally to form a 

 saucer-shaped expansion (Podophrya, Ephelota) for the support of the 

 body or (Metacineta) a protective cup for its reception during 

 retraction. 



A large number of the Acinetaria are epizoic in habit, and very 

 frequently a particular species is only found on one genus of host. 

 For example, Rhynceta occurs only on the abdominal appendages of 

 Cyclops, and Dendrocometes on the gills of Gammarus. The species 

 of Ephelota are frequently associated with particular species of 

 Hydroids ; Stylocometes is usually found on the gills of Asellus, but 

 has also been found on the colonies of Ophrydium. The species 

 of Acineta are usually found attached to water weeds. Some species 

 of Spliaerophrya after a brief free-swimming life in the water attack 

 various Ciliata and become parasitic. Endosphaera is parasitic on 

 Vorticettina and some Acinetaria. The phenomenon of conjugation 

 has been observed in Dendrocometes, Podophrya, Tokophrya, and 

 probably occurs throughout the group. In Podophrya the discs of 

 two neighbouring individuals are brought together and fusion of 

 the protoplasm of the two is thus effected. In Dendrocometes and 

 Stylocometes, however, a special pseudopodium from the body-wall 

 of each of two neighbouring individuals is produced, and these 

 meet and fusion takes place. It would be interesting to know 

 what stimulus causes these processes to form at the same time and 

 grow together. The reproduction is usually brought about by 

 gemmation. In the parasitic species of Sphaerophrya a division 

 into two equal halves takes place soon after the parasites have 

 reached their full size. This is followed by a rapid series of equal 

 divisions, and finally the spores that are thus formed develop suckers 

 and escape as small free-floating individuals. At this stage a 

 division occurs into two almost equal segments, but the smaller of the 

 two is provided with suckers and cilia, and may be regarded as a 

 bud, while the larger, which has suckers but no cilia, may be regarded 

 as a parent. There is, however, no sharp line to be drawn between 

 the processes of fission and gemmation in these animals : they are 

 probably of essentially the same nature. But the case of Sphaero- 

 phrya is interesting as it exhibits two phases of the reproductive 

 processes (fission in the parasitic form, gemmation in the free) which 

 are very closely related, but sufficiently distinct to justify a different 

 nomenclature. 



In the stalked forms Podophrya and Metacineta, the disc divides 

 horizontally into two almost equal parts, but the distal part is 

 ciliated and has no suckers, whilst the proximal part attached to 

 the stalk has suckers and no cilia. In Dendrocometes there is a 

 division into two approximately equal parts, but in this case the 

 smaller ciliated part or bud is separated from the other internally 



