32 ZOOLOGY 



Class IV. Acinetaria. 



No cilia or flagella present, but a number of tentacular 

 processes, which may be adhesive or may be tubular and 

 suctorial. The Acinetaria are usually fixed, and most com- 

 monly stalked (Fig. 26). The nucleus is single, and often 

 branched. One or more contractile vacuoles occur. Eepro- 

 duction takes place by binary fission and gemmation ; the latter 

 is often internal. 



The Acinetaria are either marine or freshwater, and they 

 are all carnivorous, living chiefly on the soft parts of Infusoria. 



Fig. 25. — Sphaerophrya magna, Maupas. x 300. 



1. IxLiWiinsls oi Colpoda panifrona, a ciliated Infus- 



orian whose soft parts are being sucked up by the 

 Spfiaerophrya. 



2. The nucleus. 



3. One of the hollow tentacles ending in a knob. 



The cuticle may be thin, but in some cases a definite mem- 

 branous capsule is formed. Two kinds of tentacles may be 

 found : one long and adhesive, whose function is to catch and 

 hold the prey ; the other is shorter, tubular, and ends in a 

 sucker, — these latter are sometimes provided with a spiral 

 thickening. The soft protoplasm of Infusoria, on which they 

 prey, is sucked up through these hollow tentacles (Fig. 25). 

 Dendrocometes has a round body, from which four to six many- 

 branched stout arms project. Each branch ends in a point, 

 which is said to be hollow, and by means of which food is 

 sucked into the body. In this genus, and in one or two others, 

 the contractile vacuole has an excretory duct. 



Acineta (Fig. 26) is a stalked form with a membranous 

 cup ; the tentacles are arranged in two clusters at each side of 

 the body. 



Eeproduction may be by fission, or by external gemmation, 

 or by internal gemmation, in which case a brood - pouch is 

 formed, which may be open, but is more commonly closed. 



