LOCOMOTION IN WATER 



225 



This somersault takes some time to accomplish, usually 

 teu to twenty minutes ; therefore at least an interval 

 of one minute should be allowed between two succes- 

 sive photographs if the various phases are to be clearly 

 depicted. 



Locomotion of Small Marine Animals.— If the move- 

 ments are small, and if they have to be studied at a 

 near distance, a special arrangement must be adopted. 

 Two cover glasses should be cemented together, and 

 a small aquarium made just about the same size as 



Fig. 158. — Movement of the appendages of a shrimp. 



the field of the intended photograph. The case is 

 then filled with sea- water, and the animal —a shrimp, 

 for instance — introduced ; by taking on a moving 

 film successive photographs, which are silhouetted 

 against a luminous background, a series of pictures 

 representing the movements of the appendages is 

 obtained. 



Further on, a similar arrangement for the study of 

 the flight of insects will be described. Finally, these 

 small animals can be studied under a microscope by 

 an arrangement presently to be described. 



