70 



Introduction to Animal Morphology. 



Fig. 8. 



branched, with (Spirochona) or without (Epistylis) a spiral 

 leaf-like appendage to the peristome. The stalk is flexible, 

 unbranched in Vorticella, and on irritation contracts suddenly 

 into a close spiral. They multiply by longitudinal fission, 

 one half, being freed from the stalk, developing a posterior 

 crown of cilia, and a mouth at that side, while a new stalk 

 grows at what before was the anterior end. Buds may form 

 at the base of the bell, or encystation may take place, the 

 nucleus splitting into monadiform bodies, each of which, be- 

 coming free, develops into an Acineta {S/ein). Carchesium 

 has a branched flexible stalk, but the muscle-band in each 

 branch is independent. Zoothamnion has a branching 

 muscle, as well as stalk, and some of the buds thereon remain 

 permanently globular and unexpanded. Urocentrum has a 

 pedicle, but is unattached. 



2. Trichodinidae — urn-like, with 

 an anterior and posterior crown of 

 cilia, peristome not capable of 

 closure. Trichodina, parasitic on 

 Hydra, has an anchor apparatus at 

 the posterior end, consisting of a 

 chitinous ring with two rows of 

 recurved uncini, and a flexible, 

 finely striated collar outside this 

 and above its base. Halteria has 

 two similar ciliary crowns, but no 

 anchoring apparatus. 



3. Ophrydinidas — often clustered, included in a sheath,, 

 seldom stalked. If the lorica be gelatinous, and by imperfect 

 division hold together the perfectly divided animals, they 

 form soft masses often over an inch in diameter (Ophrydium). 

 In isolated forms the animal may be sessile in the lorica 

 (Vaginicola), or stalked (Tintinnus), or the lorica itself may 



-be rigidly stalked (Cothurnia). 



4. Dictyocystidae are marine forms with a siliceous, per- 

 orate, bell-shaped shell like that of aRadiolarian. Codonella 

 is closely allied, with a bell-shaped perforate test and a double 

 peristome ; it is made the type of a separate family by 

 Haeckel. 



A. Oxytricha gibba. . 



B. Trachclocorca biceps. 



C. Vorticella citrina. 



