TETRASTEMMA. 49 



slightly if the trunks of the water-vascular system are not easily 

 seen. They can always be seen in preserved and stained speci- 

 mens that have been killed under pressure. If you have trouble 

 in seeing them, examine such a specimen. Do you find pro- 

 glottids? Understand the relation of this larva to a true cysti- 

 cercoid. 



Curtis: Crossobothrium laciniatum and Developmental Stimuli in the 



Cestoda. Biol. Bui., 5, 1903. 

 : The Formation of Proglottids in Crossobothrium laciniatum. Biol. 



Bui., 11, 1906. 

 Linton: A Cestode Parasite in the Flesh of the Butterfish. Bui. U. S. 



Bur. Fish., 26, 1906. 

 Tennent: A Study of the Life-history of Bucephalus haimeanus: A Parasite 



of the Oyster. Quart. Jour. Mic. Sci., 49, 1906. 



NEMERTINEA. 



Several representatives of this group are rather easily ob- 

 tained. Some of these, as some species of Cerebratulus and 

 Meckelia, are large, but they are generally unsatisfactory for 

 anatomic study, as they are opaque and filled with a connective- 

 tissue parenchyma that binds the organs together. Further- 

 more, they are especially likely to cut themselves into small 

 pieces by contraction of muscles in the body-wall. 



TETRASTEMMA. 



This small animal lives among the forms that are generally 

 found attached to piles. Specimens can usually be found by plac- 

 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. 



4 



