100 



MANUAL OF ZOOLOGY. 



fusoria which, like Peridinium, find their means of locomotion 

 in long, flexible, lash-like filaments, termed "flagella;" cilia 

 occasionally being present as well. In some, as in Peranema 

 and in the Monads (fig. 34, B), there is only a single one of 



Fig- 33- A, Stentor Miilleri; B, Vaginicola crystallina ', C, Group of Vorticella: ', 

 D, Detached bud of Vorticetta, showing the posterior circlet of cilia. 



these appendages ; in others, as in Anisonema, there are two 

 flagella ; whilst in Heteromastix (fig. 34, G) and Pleuronema we 

 have forms apparently transitional between the Ciliata and 

 the Flagellata, since both cilia and flagella are present in these 

 genera. In all their other essential characters the flagellate 

 Infusoria do not differ from the more typical members of the 

 class, with which they agree in possessing a cuticle, a firm cor- 

 tical layer, and a soft granular central parenchyma, whilst they 

 possess a nucleus and one or more contractile vesicles. They 

 have, however, the peculiarity that, in many cases at any rate, 

 the base of the flagellum is surrounded by a cup-like or cylin- 

 drical membranous collar, which can be retracted at will. 

 Many also (as Euglena, Astasia, Heteromastix} possess the sin- 

 gular brightly -coloured mass of pigment which is known as the 

 'eye-spot," and which may possibly be a species of sense- 

 organ (fig. 34). In one singular form (Phalansterium intes- 

 tinale\ the organism consists of numerous zooids, each with a 

 single flagellum and projecting membranous collar, enveloped 

 basally in slimy sarcode, so as to form a cylindrical colony. 



Another remarkable animalcule now usually referred to this 

 group is Noctiluca, which occurs abundantly in most oceans, 



