356 



METAHOEPHOSES OF ANIMALS. 



Fig. 371. 



skin, losing with it both its eyes and its tentacles. On the 

 other hand, a thick membrane lining the interior of the shell, 

 pushes out and forms a stem (e), by means of which 

 the animal fixes itself to immersed bodies, after the loss of its 

 tentacles. This stem gradually enlarges, and the animal soon 

 acquires a definite shape, such as is represented in fig. 3/0, f t 

 attached to a piece of floating wood. 



556. There is, consequently, not only a change of organ- 

 ization in the course of the metamorphoses, but also a change 

 of faculties and mode of life. The animal, at first free, be- 

 comes fixed ; and its adhesion is effected by totally different 

 organs at different periods of life, first by means of tentacles, 

 which were temporary organs, and afterwards by means of a 

 fleshy stem, especially developed for that purpose. 



557. The radiata also furnish us with examples of vari- 

 ous metamorphoses, especially 

 among the star-fishes. A small 

 species, living on the coastof New 

 England (Echinaster sanguino- 

 lentus), undergoes the following 

 phases (fig. 3/1). 



558. If the eggs are ex- 

 amined by the microscope, each 

 one is found to contain a small, 

 pear-shaped body, which is the 

 embryo (e), surrounded by a 

 transparent envelope. On es- 

 caping from the egg the little 

 animal has an oblong form, with 

 a constriction at the base ; this constriction, becoming deeper 

 and deeper, forms a pedicle, (p), which soon divides into 

 three lobes. The disc also assumes a pentagonal form, with 

 five double series of vesicles ; the first rudiments of the rays, 

 are seen to form in the interior of the pentagon. At the same 

 time the peduncle contracts still more, being at last entirely 

 absorbed into the cavity of the body, and the animal soon 

 acquires its final form (m) . 



559. Analogous transformations take place in the Coma- 

 tufa. In early life it is fixed to the ground by a stem (fig. 

 372), but becomes detached at a certain epoch, and then floats 

 freely in the sea (fig. 373). On the other hand, the polypi 



