Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 ACTINOZOA. 227 chamber* appears first, surpassing in size those which follow it. The opposite (posterior) unpaired tentacle and the other paired tentacles then make their first appearance as small wart-like prominences. When the twelve tentacles have been formed, they become alter- nately equalised, so that six larger tentacle*, amongst which are reckoned the unpaired ten- tacles of the long axis, alternate with the
Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 ACTINOZOA. 227 chamber* appears first, surpassing in size those which follow it. The opposite (posterior) unpaired tentacle and the other paired tentacles then make their first appearance as small wart-like prominences. When the twelve tentacles have been formed, they become alter- nately equalised, so that six larger tentacle*, amongst which are reckoned the unpaired ten- tacles of the long axis, alternate with the same number of smaller ones, and we have two circles of six tentacles of the first and the same number of the second order. The asexual reproduction by gemmation and fission is of great significance. Buds can be formed in various positions, even at the oral end, in which case a strobila-like form appears. In Blastotrochus the buds appear at right angles to the axis of the parent animal (fig. 171). If the individuals so produced remain connected with one another, a polyp-stock is formed, which may attain very various forms and great size. As a rule the individuals are imbedded in a common body mass, the ccenenchym, and their gastric cavities communicate more or less directly, so that the juices acquired in the in- dividual polyps penetrate into the collective stock. This stock affords us an excellent example of an animal community built up out of similar members. The formation of the generative products alone is distributed, as a-rule, to different individuals, which, however, unite in dis- FIG. 171.—Blattntrochut nutrij; (after C. Sem- per). Z-fiT, Lateral bud. charging all animal and together vcge- (fi*
Size: 1078px × 1855px
Photo credit: © Bookworm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: archive, book, drawing, historical, history, illustration, image, page, picture, print, reference, vintage
