

16 



NATURAL HISTORY. 



naturally occur if man were to make the selection. It is always the same 

 species of shrimp which occurs in the sponge, and this species has not yet 

 been obtained except from these sponges. 



Fig. 15. — A glass-sponge i Holtenia), with the glassy filaments which served to 

 r. nchor it in the muddy bottom shown below. 



