36 



ANIMAL STUDIES 



34. Distribution. The sponges are aquatic animals, and, 

 with the exception of one family consisting of relatively 

 few species, all are inhabitants of the sea in every part of 



FIG. 14. Diagrams illustrating the development of a sponge. A, egg-cell ; n, nucleus. 

 B, C, D, 2-, 4-, and 16-cell stages. E, blastula. F, section through somewhat 

 older larva. G, gastrula. H, young sponge. I, section through somewhat 

 younger larva than H. 



the globe. The larger number occupy positions along the 

 shore, becoming especially abundant in the tropics ; but 

 other species occur at greater depths, several species living 



