54: GENERAL BIOLOGY. 



(a) Large, often occupying the centre of the 



nettle-battery. 



(b) Smaller and more numerous, surround- 



ing (a). 



When a tentacle is in focus under A A 2, draw a 

 few drops of magenta under the cover-glass. 

 Observe : 



The discharge of the threads. 

 With D 2 find the threads, and also note in 

 the surrounding water discharged nemato- 

 cysts. 



(a) The larger rounded cysts do not become 



colored. 

 Note: 



The barbs. 



The long finely tapering thread. 



(b) The smaller oval nematocysts stain 



deeply. Note : 



The shorter, thicker thread. 

 Sketch both kinds of nematocysts. 

 III. Histology. 

 A. Isolated Cells. 



Tease out in dilute glycerine a hydra that has 

 been macerated and slightly stained.* Examine 

 the fragments with the highest power in a strong 



* To macerate, put for a few minutes into a mixture of glacial 

 acetic acid 1 part, glycerine 1 part, water 2-4 parts (the method 

 of Bela Haller), and stain in an aqueous solution of methyl- 

 green. 



