CROSSOBOTHRIUM, TETRASTEMMA 77 



Larval Stage. — Examine and draw a specimen of the larva 

 found in the cystic duct of the squeteague. The scolex with 

 its suckers at the anterior end, and the opening of the water- 

 vascular system at the posterior end, are readily seen. Com- 

 press slightly if the trunks of the water vascular system are 

 not easily seen. They can always be seen in preserved and 

 stained specimens that have been killed under pressure. If 

 you have trouble in seeing them, examine such a specimen. 

 Do you find proglottids? Understand the relation of this 

 larva to a true cysticercoid. 



Curtis: Crossobothrium laciniatum and Developmental Stimuli in the 



Cestoda. Biol. Bull., 5, 1903. 

 : The Formation of Proglottids in Crossobothrium laciniatum. 



Biol. Bull., 11, 1906. 

 Linton: A Cestode Parasite in the Flesh of the Butterfish. Bull. 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 1 



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 con- 

 nective-tissue parenchyma that binds the organs together. 

 Furthermore, 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 gener- 

 ally found attached to piles. Specimens can usually be found 

 by placing 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 pipette transfer a specimen to a slide, cover it, 



x This group is, by many, considered as a separate phylum. 



