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The following Letters apply in all the Plates where they are used to
corresponding parts of the structure :
cavity of the epistome and the perigastric space.
Rotatory muscles of tentacular crown.
Posterior parieto-vaginal muscles.
DESCRIPTION OF THE PLATES.
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 mem
brane, 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 mem
brane. 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 dia meters. 8. Natural size of mature statoblast.