The following Letters apply in all the Plates where they are used to

corresponding parts of the structure :

DESCRIPTION OF THE PLATES.

Fig.

PLATE I.

CRISTATELLA MUCEDO.

1. Cristatella mucedo; an adult specimen, adhering to the submerged stem of Ranunculus aquatilis. Of the natural size.

2. The same enlarged.

3. Statoblast of Cristatella mucedo in an early stage; it is surrounded by a ciliated membrane, and there is as yet no appearance of the marginal spines.

4. The same more advanced; the enveloping membrane is destitute of cilia, and the spines have begun to grow out from the margin of the disc.

5. The same, still further advanced; the spines have impinged on the enveloping membrane.

6. The mature statoblast; the enveloping membrane has been torn by the pressure of the spines, and has disappeared, and the statoblast has become free.

7. The same, viewed on the edge. Figs. 3-7 are magnified about 50 diameters.

8. Natural size of mature statoblast.