358 ZOOLOGY 



3. Invert the starfish ; observe and record the changes undergone in 

 reassuming the normal position. 



TOPICS FOR FURTHER STUDY 



1. Habitat of starfish. 2. Food and economic importance. 3. Gen- 

 eral history of development. 4. Allied forms ; Solaster and other 

 starfishes, brittle stars, sea-urchins, holothurians, crinoids. 



XIV. HYDRA 



This exercise requires the use of a lens. 



To obtain Hydra it will be necessary to search carefully in fresh- 

 water pools. Lemna together with sticks and grass should be 

 collected from the pools and put into an aquarium. The Hydras, 

 which are attached to these objects, will then usually migrate in the 

 course of a few days to the light side of the vessel, where they can 

 be easily found. Hydras can be kept readily throughout the entire 

 winter in a large glass jar containing Lemna and other plants, and 

 Entomostraca for food. All the following exercises can be done on 

 the living animal, and either the brown species (//. fusca) or the 

 green species (H. viridis) may be employed. 



DRAWINGS 



(From living individuals') 



1. Side view of a single Hydra, not budding, x 10. 



2. Side view of a Hydra with buds, x 10. 



(Optional, requires compound microscope.) Draw one of the ten- 

 tacles of Hydra, showing discharged and undischarged nettling 

 capsules, x 300. 



OBSERVATIONS ON THE LIVING ANIMAL 



Each student should be provided with the following: (1) 4-inch 

 battery jar ; (2) 2-inch Stender dish ; (3) vial containing 5 % sugar 

 solution ; (4) vial containing 5 % acetic acid ; (5) a few Daphnias in 

 a watch-glass ; (6) pipette ; (7) needle ; (8) watch-glass ; (0) paste- 

 board box of a slightly larger size than the battery jar and with a 

 vertical slit half an inch wide along one side. 



Place a Hydra in a watch-glass full of water. 



