DENDROCOMETES PARADOXUS. 327 



Enrope ifc also appears to be generally distribntecl. It 

 certainly occurs in Belg'iutn (Sand), France (Maupas), Ger- 

 many (Butschli, Plate, etc.), Russia (Wrz.). It also occurs 

 in North America (BiitschliJ. It is probable that the Den- 

 drocometes which occur on the gills of Gammarus 

 putaneus (Lachmann) may be a distinct species, but, apart 

 from this, Dendrocometes only occurs on the gills of Gam- 

 mams pulex, although exceptionally a few specimens 

 may be found attached to the hairs on the legs of the same 

 host (Sand). 



Dendrocometes paradoxus has a planoconvex-shaped 

 body, and is provided with three, four, or five arras (PI. 17, 

 fig. 1). The morphology of these arms is a matter of some 

 dispute, but it is not an unreasonable view to regard them as 

 homologous with a bundle of Acinetarian tentacles. They 

 capture, kill, and partially digest the pvey in the same manner 

 as the tentacles and suckers of other Acinetaria. The body 

 contains a single large meganucleus, and a variable number, 

 but usually three, micronuclei. There is a single large con- 

 tractile vacuole. Reproduction is effected by an interesting 

 process of internal gemmation, first described by Butschli 

 (1). The single planoconvex bud that is formed is fre- 

 quently called the " embryo," but I think it is more appro- 

 priate to call it the ''gemmula." It escapes from the 

 parents without arms, but provided with a girdle of three 

 bands of cilia, and swims away. 



From time to time, or perhaps, under certain conditions 

 only, nearly the whole substance of an individual escapes from 

 the pelHcullar sheath and swims away from the gill in a form 

 which cannot be readily distinguished from a gemmula. 



With this brief introductory account of the sti-ucture and 

 reproduction of the animal I pass on to the phenomena of 

 conjugation, to which I have paid special attention. 



Part I. — Conjugation. 



The phenomena of conjugation in Dendrocometes may be 

 briefly stated as follows : 



