226 Introduction to Animal Morphology. 



in the surface of the ectocyst. 2. Vibracula, consisting of an 

 oval capsule with no basal part, ending in a long seta like the 

 lower jaw of Avicularia. 3. Oocysts globular marsupial 

 cells, found in Chilostomata, receiving the eggs on extrusion. 



Each persona consists of an oval sac filled with a 

 watery, corpusculated fluid, extending into the ten- 

 tacles, and in which the digestive canal floats. The 

 mouth of this canal can be partly protruded from the 

 cell by evagination, and can be retracted at will. 

 The mouth is simple, projecting, contractile ; its epi- 

 stome, when present, is globular or pyramidal, hollow, 

 ciliated externally, and raised by a special inner 

 muscle. A muscular pharynx leads by a ciliated 

 oesophagus into the non-ciliated intestine, from which 

 a caeca! stomach depends, whose cardiac and pyloric 

 orifices are close together above. The intestine at 

 first widens, leads backward, and then, narrowing, 

 opens by an anus close to the mouth, but external to 

 the tentacles. The flexure of the digestive canal is 

 always concave towards the nerve ganglion. The 

 walls of the canal consist of an outer, thin layer of 

 contractile fibre-cells, disposed circularly, and an inner 

 of small, simple (hepatic) cells, thick, green, or brownish 

 in the stomachs of many genera. Marine forms have 

 often knotty thickenings of their muscle fibres. The 

 stomach is gizzard-like in many of the Ctenostomata, 

 and often contains chitinous teeth. In Bowerbankia 

 it has two opposed balls of dark, radiated fibres, and 

 is lined by small chitinous plates ; in action the balls 

 elongate and approximate, and the radiating fibres 

 become parallel. Hislopea has a somewhat similar 

 gizzard. There is no vascular system ; the perivisceral 

 fluid nourishes the tissues, and is renewed by osmose 



