164 ZOOLOGY. 



varying degrees in intimacy. Fossil sponges, apparently of 

 the same general characteristics as those now living, are found 

 in very early geological strata. 



211. Supplementary Library Studies. 



1. Economic value of sponges. Sponge fisheries. The mode of pre- 

 paring sponges for market. 



2. What arguments may be advanced for considering the sponges as 

 colonial Protozoa? What is the conclusive argument for regarding them 

 as Metazoa? 



3. By comparing the figures of sponges found in your reference books, 

 note the different degrees of development of the passages lined with ento- 

 derm and ectoderm in the walls of various species. 



4. In what special ways do sponges become adapted to the conditions 

 in which they are situated? Effect of rapid currents on them? Of quiet 

 water? Of muddy water? 



