sow SPOJVOeS GROW. 



17 



openings for tlie exit of waste matters. Among tliese large 

 openings are multitudes of minute openings wiiieli serve as 

 moutlis. Tliese mouths lead by branching canals into little 

 pockets or chambers which are lined with digestive, ciliated 



Fig. 15. — Development of a sponge (Fiycon ciliatum). A, B, morula seen in sec- 

 tion; c, segmentation cavity; C, blastula stage ; D. gastrula about to be- 

 come stationary, with a few spicules; £, sponge become stationar}', with 

 spicules. Highly magnified. 



cells; the sponge, then, has myriads of mouths and stom- 

 achs (Fig. 14). 



Sponges develop, like all the 

 higher animals, from true eggs. 

 The egg, after fertilization, 

 begins to grow, and divides into 

 two, four, eight, sixteen, and 

 more spheres, until it looks like a 

 mulberry, which seen in section 

 is as in Pig. 15, .^4, i?. This is the 

 segmentation stage or morula. 

 The cells farther multijjly, and 

 arrange themselves into a single fig. le.— ciliated embryo or bias- 



1 1 ii 1, • 11 J tula of a sponge (&';/cant/7Tf ?'a- 



layer, when the embryo is called phanus). (Hifhiy magnified.) 

 a blastula. Some of the cells are 



ciliated, and as a blastula the embryo leaves the parent 

 sponge and swims about in the sea (Fig. 16 and Fig. 15, C). 



