TETRASTEMMA. 45 



ing scrapings from piles in a glass jar with a little sea-water and 

 allowing them to stand from a half hour to three hours. The 

 animals may then be found, with the aid of a lens, on the sides 

 of the dish, usually near the surface. 



With a pipet transfer a specimen to a slide, cover it, and 

 examine with low and high powers of the microscope. Notice: 



1. The shape of the body, the four eye-spots, and the ciliated 

 grooves. 



2. The straight alimentary canal. The diverticula of the 

 intestine and the terminal anus. 



3. The enormous proboscis, consisting of a large anterior 

 eversible portion, and a smaller posterior portion that is not 

 eversible. When the proboscis is retracted it is bent upon 

 itself. Stylets are present in the eversible portion, near its 

 inner end. Can you determine how the proboscis is protruded 

 and retracted? Does the proboscis have anything to do with 

 the digestive system? 



4. Beneath the posterior eye-spots are the cerebral ganglia, 

 from which lateral nerve cords extend posteriorly. 



5. If the specimen happens to contain eggs, they will lie 

 between the diverticula of the intestine. They are compara- 

 tively very large. 



