DEVELOPMENT OF EGGS IN MANY-CELLED ANIMALS 343 



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Fig. 



-Stages in Development of a Sponge, enlarged (except 10) to various scali^s 



f, Ectoderm ; /, enduderni ; g, digestive cavity; o^ main opening (osculum) of digestive cavity ; p, pore in 

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

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

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



