218 Animal Micrology 



the sponge with strong nitric acid or a mixture of nitric and 

 hydrochloric acid. 



. COELENTERATES 



Hydra should be sought for in spring-fed pools. In the 

 autumn they are found most frequently on smooth dead leaves 

 which are completely submerged. Material should be collected 

 and placed in battery jars or larger glass jars, which are then 

 filled with fresh, clear water and placed in a fairly light place, but 

 not too near a window. Put a small amount of horn wort or Chara 

 in each jar. In a few hours ( 12-36) the hydra will be found attached 

 to the sides of the vessel and to the plants. They may readily be 

 kept in the laboratory throughout the winter if glass plates are 

 placed over the jars to prevent excessive evaporation and the 

 temperature is not allowed to go below freezing. Fresh water 

 should be added from time to time to make up for evaporation. 

 In case their supply of food (Cyclops, Daphnia, and other small 

 Crustacea) is exhausted it should be renewed by skimming out 

 from other aquaria the small forms upon which the animal feeds 

 and putting them in the hydra jars. 



For staining and mounting entire see chap, xiii II, B. Kill in 

 the same way for sectioning. The most instructive sections are 

 (1) transverse sections, (2) longitudinal sections through the 

 mouth and a bud, and (3) sections showing the sexual organs. 

 Stain in bulk with hematoxyliii (reagent 49, Appendix B), imbed 

 in paraffin using the method for delicate objects (chap, vi, VII), 

 and after the paraffin has been removed from the sections, stain 

 them for a few seconds in acid fuchsin. Dehydrate and mount in 

 the usual way. 



The sections are much more satisfactory if the hydra have been 

 placed in small stender dishes filled with filtered water (not dis- 

 tilled) and kept from food for a week or ten days before killing. 

 This eliminates the metabolic products and oil globules which 

 ordinarily obscure the details of structure. 



To Stain the Nematocysts of Living Hydra, place several of the 

 animals in a small stender dish of water which has been tinted a 



