THE DEVELOPMENT OF ZOOPHYTA. 289 



time, however, the disc becomes completely surrounded by the 

 arch of cilia, (d,) and during the process gradually assumes a 

 position similar to that of the adult, i. e., obliquely transverse to 

 the longitudinal axis of the body. 



ZOOPHYTA. 



Of the four classes of this division, namely, the Polypi, 

 Acalephue, Ctenophorae, and Echinodermata, I shall illus- 

 trate the development of only 

 the first and the last, which are 

 respectively the lowest and the 

 highest of the group. The 

 mode of growth of the young 

 of the Acalephse has been 

 sketched already when treating 

 of the process of self-division, nii 

 and the orientation of the ten- 

 tacles of Aurelia and its ephyra Fl s- 190- 



and scyphostoma* 



Polypi. After undergoing the usual process of segmentation, 

 the egg of the Sea-anemone (p. 57, fig. 28) loses its peculiar 

 character, and becomes transformed into a solid oval mass (fig. 

 190, I). Presently one end of it becomes indented (II, m) ; then 

 in process of time the indentation deepens until it reaches the 



Fi<j. 190. The several stages of development of a Sea -anemone, slightly 

 magnified. I, the first stage after the segmentation of the yolk. II, the second 

 stao-e ; m, the incipient digestive cavity. Ill, the third stage ; f/c, the future di- 

 gestive cavity ; b, the solid, vase-like body. IV, the stomach proper beginning 

 to form by an inrolling (wi 1 ) of the rim of the vase; f/c, the digestive cavity; b, 

 the base. V, the stomach in an advanced state of development; m 1 , the pos- 

 terior edge of the stomach ; f/c, the digestive cavity.; ?, the feelers ; p, the incip- 

 ient semi-partitions ; 5, the wall of the body. VI, the stomach completed ; m, 

 the mouth ; m 1 , the posterior opening of the stomach (sf) ; dc, the digestive 

 cavity ; p, the semi-partitions ; f, the feelers ; 6, the wall of the body. From 

 Colloid. 



* See p. 241 for the description of the earliest stages of development, and 

 p. 67 for the completion of the process, up to the adult condition. 

 19 



