SPONGES AND ZOOPHYTES. 



129 



eighty seconds. Besides the foregoing movement, a regular flow of fluid 

 carrying with it solid particles of various sizes, may be observed along the 

 whole length of the stem, passing in a somewhat spiral direction. It is 

 worthy of mention here, that when a Tubularia is kept in confinement, 

 the polype-heads almost always drop off after a few days, but are soon 

 renewed again by a new growth from the stem beneath; and this exuvi- 

 ation and regeneration may take place many times in the same indi- 

 vidual. 1 



519. It is in the Families Campanularida and Sertularida (whose 

 polyparies are commonly known as ' corallines '), that the horny branch - 



FIG. 356. 



FIG. 357. 



Development of Medusa-buds in Syncoryne 

 Sarsii : A, an ordinary polype, with its club- 

 shaped body covered with tentacles: B, a pol- Sertularia cupressina : A, natural size; B, portion 

 ype putting forth Medusoid gemmae ; a, a very magnified, 



young bud; 6, a bud more advanced, the qua- 

 drangular form of which, with the four nuclei 

 whence the cirrhi afterwards spring, is shown 

 at d ; c, a bud still more advanced. 



ing fabric attains its completest development; not only affording an in- 

 vestment to the stem, but forming cups or cells for the protection of 

 the polypites, as well as capsules for the reproductive gonozooids. Both 

 these families thus belong to the Sub-order Thecata. In the Campanu- 

 larida the polype-cells are campanulate or bell- shaped, and are borne at 

 the extremities of ringed stalks (Plate xx., c); in the Sertularida, on 

 the other hand, the polype-cells lie along the stem and branches, at- 



1 The British Tubularida form the subject of a most complete and beautiful 

 Monograph by Prof. Allman, published by the Ray Society. 

 9 



