THE INFUSORIA 455 



the body, leads into a short oesophagus. The nucleus is single, without a 

 micronucleus. Schewiakoff makes Maupasia the type of a distinct order of 

 the Ciliata the Mastigotricha. 



Monomastix ciliatus (Fig. 189, A), described by Roux (862), and referred by 

 him also to the Mastigotricha, has an even coat of cilia all over the body, and 

 possesses two macronuclei, near each of which is a micronucleus ; its most 

 remarkable feature is the possession of a long flagelluni implanted at the 

 anterior end of the body close to the mouth. 



From these various considerations, it seems highly probable that the Ciliata 

 are descended from flagellate ancestors ; but it is not possible at present to 

 indicate with any approach to exactness the line of descent. 



SUBCLASS II. ACINETARIA (Suctoria, Tentaculifera). 



The Acinetaria are distinguished from the Ciliata by the posses- 

 sion of the following characters in combination : The adult organism 

 is of sedentary habit, and has no cilia, though the youngest stage 

 in the life-history is typically a free-swimming ciliated organism ; 

 there is no mouth, but both the capture and ingestion of food is 

 effected by means of special organs peculiar to this subclass, and 

 known as tentacles. 



An acinetan may be attached to various objects, and is frequently 

 epizoic. Some species attach themselves indifferently to a living 

 or a lifeless object ; others are constantly epizoic, and occur always 

 attached to some particular animal, frequently to a particular 

 organ of it. Very few species, however, are truly parasitic in the 

 adult condition ; on the other hand, many species are parasitic in 

 the early larval stages of their life-history, and frequently so within 

 the bodies of Ciliata (Fig. 192). The marine genus Ophryodendron, 

 however, is a true ectoparasite of hydroids, according to Martin, 

 and contains nematocysts derived from its hosts. In this case the 

 parasitism is correlated with a peculiar dimorphism of " proboscidi- 

 form " and " vermiform " individuals, the former possessing a tuft 

 of tentacles on a proboscis-like process, the latter being without 

 tentacles altogether. The vermiform individuals are budded from 

 the proboscidiform, and either form can produce ciliated buds, 

 which develop into proboscidiform individuals again ; but the 

 vermiform type does not grow into the proboscidiform. In Den- 

 drosomides paguri, however, Collin (881) finds that similar vermi- 

 form individuals become transformed into the tentacle-bearing 

 form. In Rhabdophrya trimorpha, ectozoic on a Copepod (Cletodes 

 longicaudatus), there are three forms of individuals namely, in 

 addition to tentaculated and vermiform specimens, peculiar " unci- 

 forni " individuals, which are also without tentacles (Chatton and 

 Collin, 876). 



The form of the body varies greatly, but may be said to be 

 typically vase-like, with or without a stalk or peduncle. In sessile 

 forms the body is attached by a broad base to the substratum. In 



