PRACTICAL ZOOLOGY 31 



off and a drop of the sediment in the tube placed under 

 the microscope for examination. If a fragment of 

 Grantia be placed in 'weak acetic acid, an abundant 

 effervescence will take place, giving evidence that the 

 spicules are composed of carbonate of lime, the rest of 

 the sponge body remaining undissolved. 



In studying the toilet sponge, note its color, shape, 

 weight, and elasticity ; study the position and arrange- 

 ment of the large and small canals ; note the embedded 

 sand particles, shells, etc. ; the texture of various speci- 

 mens; put a fragment under the low power of the 

 microscope and note how the fibers are arranged ; soak 

 a sponge in water and measure the amount held in the 

 meshes by squeezing it out into a graduate. 



Fresh-water sponges are not easily kept alive in the 

 laboratory nor is their structure very plain. Their mode 

 of growth, branching, color, and friable texture may be 

 studied. With a magnifying glass numerous pores will 

 be seen on Spongilla, while the oscula of Myenia are 

 plainly visible. Microscopic sections will show the 

 double-pointed, flinty spicules traversing the tissues in 

 all directions. Small spherical, seedlike gemmules may 

 be obtained in the older part of the sponge in the fall, 

 and will " germinate " in a few days if kept undisturbed 

 in a dis4i of water. Only very little growth is likely to 

 take place. 



Coelenterata 

 Hydra 



Material. Either the green or the brown species 

 may be used ; the latter, being much the larger, is 

 preferable. It will be found attached to the stems of 

 water plants which may be kept in aquarium jars. 

 The animals will often migrate to the sides of the 

 jar, where they can be studied with or without a lens. 



