22 ANIMAL FORMS 
24, 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 
jee 
il. 
E 
a 
A 
Ea 
Nest 
Fie. 11.—Diagrams illustrating the development of a sponge. A, egg-cell; m, nu- 
cleus. B,C,D, 2-, 4-, and 16-cell stages. E, blastula. F, section through some- 
what older larve. G, gastrula. H, young sponge. I, section through somewhat 
younger larve 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 
