X.] THE FRESH-WATER POLYPES. 99 



LABORATORY WORK. 



1. Put in a beaker some water containing bodies to 

 which Hydrae are attached and place the beaker in a 

 window not exposed to direct sunlight : in the course 

 of some hours many Hydrae will be found attached to 

 that side of the glass which is turned towards the 

 light. Note their size, form, colour, mode of attach- 

 ment and movements. 



2. Transfer a Hydra, by means of a pipette, on to a 

 slide ; cover in plenty of water with a large coverslip, 

 and examine with 1 inch obj. Note 



a. Form. 



a. The base (so called foot): a flattened disc ; nar- 

 rower or wider than the body according to the 

 state of extension of the latter. 



/3. The body proper: cylindrical, varying much 

 in length and diameter with the state of exten- 

 sion of the animal ; its conical free end, with 

 an opening (mouth) in it. It is often difficult 

 to see the mouth in this way, especially in the 

 green species. It is readily seen however if a 

 Hydra be placed in a drop of water, without a 

 coverslip, and be watched with an inch objec- 

 tive until it turns its anterior end up towards 

 the observer. 



7. The tentacles: ranged round the mouth their 

 number and shape ; their varying length and 

 diameter ; the knob-like eminences on them. 



7-2 



