THE INFUSORIA 



371 



from cilia, however, in their movements, which are intermittent 

 and relatively slow, and also in their considerable powers of re- 

 traction, which is accompanied by the 

 appearance of a spiral ridge (Fig. 14). 

 According to some authors there 

 is a further difference from cilia in 

 the presence in the suckers of a cen- 

 tral lumen or canal. It is quite 

 probable that the protoplasm in the 

 axis of the tentacles is more fluid 

 than at the periphery, and therefore 

 gives the appearance of a canal ; but 

 it is very improbable that in any Fl - in- 



forms a true Open lumen OCCUrS. Ephelota gemmipara, Hertwig, a stalked 



r i T /v. p ,1 Acinetarian, showing both tentacles and 



The Suckers differ from the ten- suckers on the disc, b, b, contractile 



tacles in being usually uniformly ESS*"* (After *' Hertwig-) X 10 ' 

 cylindrical in shape, and by ending 



in blunt, swollen, or cup-shaped extremities. They are frequently 

 extremely extensible (Fig. 15), and exhibit during retraction a 

 spiral thickening similar to that of the tentacles. 



The arms of Dendrocometes (Fig. 85) and Stylocometes 

 have probably arisen by the fusion of bundles of 

 tentacles or suckers. They bear at their extremities 

 short papilliform or filiform processes which perhaps 

 represent the free ends of the individual tentacles of 

 which they are composed. 



The retraction of the tentacles or suckers may be 

 rapid or slow, and very frequently during the retraction 

 a spirally arranged ridge appears on the surface, which 

 may be regarded as the specially contractile filament 

 of protoplasm which is concerned in the retraction. 

 The arms of Dendrocometes and Stylocometes are also 

 occasionally withdrawn to the level of the general sur- 

 face of the body, but this process takes from two to 

 three hours to accomplish, and is not accompanied by 

 any spiral thread appearance. 



TRICHOCYSTS occur almost exclusively in the Holo- 

 tricha. They are spindle-shaped rodlets situated in the 

 cortex close to the pellicle, having the power of suddenly 

 shooting out a thin thread-like process when influenced 

 FIO. 15. by certain stimuli. In Paramoecium (Fig. 46) they are 

 A single sucker 4 /* in length and in Dileptus 12 /*,- but no further 

 tarian" (After details of their structure have been satisfactorily de- 

 x a soo e Kent ' ) scribed. In a few instances it has been observed that 

 the exploded trichocysts have had a paralysing effect 

 upon minute organisms, and by analogy it may be assumed that 



