STATOBLASTS. 107 



muscles causing a folding in that forward part of the body-wall called 

 the tentacle sheath, as seen in the 2nd, 3rd, and 5th zooids counting 

 from the left in Fig. I., PI. IX. 



A thin membrane protects the bases of the tentacles, which are 

 ciliated on both surfaces. A well- marked ciliated lobe, the epistome, 

 overhangs the mouth (cp.). 



The alimentary canal hangs as a Y-shaped bag, suspended freely in 

 the body cavity, and in all the fresh-water forms except Paludicella, the 

 body cavity (coelome) is common to all the zooids — no partitions are 

 found anywhere — and cilia cover the whole coelomic surface. The 

 oesophagus is straight. Notice, as it enters the stomach, how it is 

 furnished with a valvular arrangement (v.) projecting downwards and 

 designed to prevent any backflow from the stomach. The latter has 

 a great pendant bag-like region, the glandular caecum, forming the 

 straight part of the Y-shape. A strong cord, the funiculus, attaches 

 the caecum to the outer wall or ectocyst. The intestine is short and 

 straight and lies parallel with the oesophagus ; the anus (a.) opens close 

 to the base of the lophophore. 



The food consists of microscopical organisms, chiefly infusoria, spores 

 and the like, swept into the mouth by the currents produced by the 

 waving of the tentacular cilia. 



The nervous system is again confined to a small double ganglion 

 lying between the oesophagus and the anus and giving off branches 

 to the lophophore. A delicate commissure surrounds the oesophagus. 

 No special sense organs are known. 



No heart is present ; the coelomic fluid, wherein corpuscles float, 

 courses freely through all parts of the colony, kept continously in 

 motion by the cilia of the internal surface. Aeration is secured in the 

 thin-walled tentacles which are hollow, branches of the coelom being 

 continued into them. 



Eepboduction. — The fresh- water bryozoa are hermaphrodite. 

 Usually the testis is situated on the funiculus (/.), while the ovary is 

 placed towards the forward end of the body (p.), and derived from the 

 endocyst or lining of the ectocyst or cuticle. 



In addition to this, the fresh- water Bryozoa are remarkable for an 

 asexual reproduction by means of winterbuds or statoblasts. Upon 

 the approach of winter, the era of dissolution for the adult colony, 

 buds are formed on the funiculus ; the cells at one end of the bud 

 grow round the remainder and form two convex horny plates attached 

 by their margins to one another, and with air cells arranged in a 

 marginal ring. In Plumatella, which we are now describing, the 

 statoblast is plain, but in Cristatclla it is an exceedingly beautiful 

 object, studded with minute knobs and provided with barbed spines 



