iQii.] N. Annandai.e : Ctenostomatous Polyzoa. 199 



number of tentacles is variable but is usually some multiple of 

 four. The collar is unusually ample and is supported by delicate 

 chitinous chaetae. Immediately below the cardia there is a short 

 glandular portion of the alimentary canal, tubular in form, which 

 lies at right angles to the main axis of the zooecium when the 

 polypide is retracted. This opens into the spherical chamber, 

 which is relatively large and bears a thick chitinous lining that 

 has the appearance in optical section of a couple of vertical ridges. 

 The compressor muscle (pi. xiii, figs. 10, 11) covers the whole of 

 the chamber but only extends over the glandular region above it 

 in the form of isolated fibres. In preserved specimens the cham- 

 ber appears to open directly into the stomach but in living speci- 

 mens the ring separating the two and bearing the cardiac cilia 

 can be extended in a vertical direction to some length. The 

 parietal muscles are reduced to three or four stout strands on 

 either side of the zooecium and there is not a definite funiculus. 

 The gonads are borne on the zooecial wall at each side of the 

 polypide. 



Hislopia lacustris, Carter. 

 (PI. xiii, figs. 9, 10, II.) 



Owing to rapid lateral and terminal budding at the base of 

 the zooecia and to the absence of intervening tubules, well-devel- 

 oped zoaria constitute, in the typical form of the species, an almost 

 uniform flat layer which has much the same appearance as that 

 of many Cheilostomata {e.g , Menihranipora) and also of certain 

 Ctenostomata of the division Alcyonellea {e.g., Flustrella). A 

 careful analysis of the method of budding, however, shows that 

 it is always of the cruciform type, whereas in Menihranipora more 

 than one lateral bud is produced at each side of the zooecium and 

 in Flustrella the method of budding is radiate, numerous linear 

 series of zooecia radiating out from a single parent-zooecium but 

 pressed so closely together as to be practically parallel to one 

 another. The form of the zooecium, especially in luxuriant zoaria, 

 is very variable; it is typically oblong but may be oval, triangular 

 or almost circular or even square. The dorsal surface is usually flat 

 and always has a hyaline transparency, but if the zooecia are closely 

 crowded together on a narrow support such as the stem of a 

 slender water-plant they are often arched above and of a consider- 

 ably greater depth (pi. xiii,. fig. 9) than if they have plenty of 

 room for expansion. In such cases the thickened margin is often 

 practically obsolete. The orifice is surrounded by a thick chitinous 

 rim which usually has a quadrate form and bears a spine at each 

 corner ; but sometimes it is circular, and the spines not only vary 

 in length but are often reduced in number or altogether absent. 

 The tentacles vary in number from 12 to 20. 



The structure of the cardiac region of the alimentary canal 

 has a certain resemblance to that found in Bowerhankia (Vesi- 

 cularina), the spherical chamber having the same position as and 



