72 THE BIOLOGY OF THE ANIMAL 



closely joined together as in a membranous 

 tissue, or do they readily separate from one 

 another? What do they contain? Do you 

 find that the cells bear any definite relation to 

 the spicules? Examine some of the spicules 

 more carefully, and note the dark line (cavity?) 

 running through the middle. Kun a drop of 

 acetic acid carmine under the cover -glass. 

 What changes take place in the cells ? In the 

 spicules ? Can you find nuclei in the former ? 

 Mount a fresh preparation and run a drop of 

 hydrochloric acid under the cover-glass. What 

 effect has the acid on the spicules? If the 

 spicules dissolve, forming bubbles, they are 

 composed of carbonate of lime, the bubbles 

 being carbon dioxide; if the spicules remain 

 undissolved they are composed of flint, this 

 substance and carbonate of lime being the ma- 

 terials of which the spicules of various sponges 

 consist. 



Look for the statoblasts, amphidiscs, or 

 gemmules, yellowish toothed disks connected 

 by a rod-shaped piece, which are formed in the 

 autumn and serve to reproduce the sponge in 

 the following spring. 



PHYSIOLOGY 



a. Movements. — Can you tell from watching the Mving 

 Spongilla, and noting especially its mode of at- 

 tachment, whether or not it can move from place 

 to place ? How does it compare in this respect 

 with the toilet sponge, judging entirely by what 

 vou have observed in the structure of the latter ? 



