DEVELOPMENT OF EGGS IN MANY-CELLED ANIMALS 343 



3. 



Fig. 862. Stages in Development of a Sponge, enlarged (except 10) to various scales 



e, Ectoderm; /, endoderm ; g, digestive cavity; o, main opening (osculum) of digestive cavity;/, pore in 

 oody-wall. i, Ovum. 2, First division of ovum. 3, Morula. 4, Two-layered embryo (in section). 5, Ciliated 

 Planula, drawn at 6 in section. 7, Later fixed stage (in section at 8). 9, Adult stage (side-wall partly re- 

 moved) showing numerous pores and three-rayed spicules. 10, Colony formed by budding. 



