120 MICROSCOPICAL STUDIES. 



designed to aid in the dispersal of these resting buds. The marginal 

 air-cushion found both in this genus and also in Pliimatclla and other 

 fresh-water Bryozoa, has obviously a similar duty. In Fig. 1, PI. IX., 

 a string of statoblasts in various stages of development is seen upon 

 the funiculus of each zooid ; while Figs. 2 and 3 give side and face 

 views of a single statoblast. The marginal air-cushion in mature buds 

 shows under the microscope as a broad black border. The statoblasts 

 becomes free upon the death and decay of the parent, rising to the 

 surface and floating at the mercy of the currents. In some genera, as 

 Pcctinella and Cristatella, the whole parent stock breaks free and floats 

 freely hither and thither an additional help in the dispersal of the 

 statoblasts. The latter remain without change during winter. In 

 spring, under favourable conditions, the valves open, and a tiny mina- 

 ture of the parent zooid emerges. It floats passive for a while, then 

 makes fast to some object, generally a water-weed, and soon by active 

 budding becomes a colonial parent. 



The asexual reproduction of the fresh-water Sponge by similar 

 resting buds should be remembered evidently a method towards 

 the perpetuation of the species induced by similarly exceptional 

 requirements. 



The Gymnolsemata, which are all marine, save Paludicella, are 

 infinitely more numerous and in form more diverse. Fig. 13 gives a 

 fair diagrammatic idea of their structure, while Fig. 12 shows the same 

 in a state of retraction. They differ from the fresh- water forms in the 

 lophophore being circular and not crescentic, in frequently having the 

 sexes separate, and in having no asexual reproduction by statoblasts. 



Bowcrbankia imbricata is a typical species, often cast up on our coast 

 attached to the brown-podded sea-weed Halidrys. Fig. 6 shows a 

 branch, natural size, while Fig. 7 shows a cluster of individuals. The 

 cuticle is chitinous, and the zooids are very similar to the diagram 

 given, save that they have a well-marked gizzard at the fore part of 

 the stomach. 



Figs. 8 and 9 show the calcareous framework of a pretty little 

 Bryozoon called Lichenopora hispida (Fleming), often found in caves at 

 extreme low-water mark within the Laminarian zone. It may also 

 be procured in dredging over coralline bottom, attached to the great 

 massive Lcpralia, another calcareous Bryozoon. 



Lichenopora^ the Cup-Coralline, as it may be appropriately named, 

 is about | in. to in. in diameter ; a snowy-white fragile porcelain 

 cup, from whose hollow arise tubular columns, each the home of a 

 delicate zooid. The calcareous wall of this tube is equivalent to the 

 horny or gelatinous ectocyst or cuticle of Plumatella or Lopliopus. In 

 the centre of cup are usually one or two elevated trumpet-shaped 

 openings, the ooecia or receptacles for the ova. 



