370 



THE INFUSORIA 



Fio. 12. 



advocated by Maupas that they represent a bundle of fused cilia 

 appears to be the most reasonable one to adopt. 



The membranes which occur in some of the Ciliata in place of 

 cilia may be regarded as due to an increase in the membranellae or 

 webbings which are not infrequently found at the base of the rows 

 of cilia previously mentioned (Fig. 70). 



These membranes, however, are so delicate that it is difficult to 

 find any trace of the individual cilia of which it is supposed they 

 are mainly composed. The spiral membrane of Spirochona (Fig. 22) 

 is, in form, so similar to the spirally arranged rows of cilia round 

 the vestibule in other CILIATA, and the collar- 

 like membrane of Torquatella (Fig. 12) is so like 

 the crown of cilia in the allied genus Strombidium 

 (Fig. 65), that the burden of proof that they 

 are not formed by the fusion or amalgamation 

 of rows of cilia falls upon those who maintain 

 their independent origin. 



In the ACINETARIA it appears that two 

 Torquatella typica, phases of life regularly occur a free-swimming 



Lank ester, found asso- r J 



ciated with the eggs of phase and a fixed or sedentary phase. In the 

 Thefmouth ts orerhuifg former, cilia occur arranged in bands or patches 

 by a crescent -shaped wn i c h do not differ in any essential respect from 



epistomial lobe, and * 



there is a membranous those found in ClLiATA. In the latter phase, 



fringe on the circumoral , . .,. . -i r 



disc. however, the cilia disappear, and a number ot 



processes are formed which are 

 called tentacles, suckers, or arms according to their 

 shape, size, and general features. The morphology 

 of these processes is not clearly understood. 



In Rhynceta cyclopum (Fig. 13) there is only one 

 elongated process, ending in a suctorial extremity. 

 This process is on the one hand similar to the 

 suckers of other Acinetaria, and on the other hand 

 might be regarded as the attenuated hypostome 

 bearing the mouth of this remarkable form. If we 

 regard Rhynceta as a primitive form, the suckers of 

 the Acinetaria might be regarded as formed by a 

 multiplication of the mouths and hypostomes of a 

 remote ancestor similar to Rhynceta, and the tentacles 

 and arms as modifications of these primitive 

 hypostomes. Such an elaborate hypothesis is not 

 necessary, and there is no reason why all these 

 processes of the Acinetaria should not be regarded 

 as highly specialised cilia or cirri. 



The simplest forms of tentacles are delicate 

 pointed processes which in their fully extended condition have 

 the same appearance as large cilia or small cirri. They differ 



FIG. 13. 



Rhynceta cyclo- 

 pum, Zenker, an 

 Acinetarian with a 



tractile 

 X 150. 



vacuole. 



