STRUCTURE OF THE A.MAROUCIUM TADPOLE 73 



DEFINITIONS 



For the purposes of description, the part of the tadpole which 

 contains the adhesive papillae and precedes during locomotion 

 will be referred to as the anterior portion; the tail, as marking 

 the posterior part of the body, and the sensory-vesicle, conspicu- 

 ous on account of its pigmented sense organs, will be desig- 

 nated as dorsal in position. The relation the body of the tad- 

 pole bears to that of the sessile ascidiozooid has been discussed 

 by Maurice et Schulgin ('84). A general readjustment of parts 

 takes place during metamorphosis in which the anterior part 

 of the tadpole becomes the basal portion of the ascidiozooid. 



FORM AND SIZE 



The general form of this and other ascidian larvae at once 

 suggests that of the amphibian tadpole, hence the name 'tad- 

 pole' has been applied to both, but the similarity between ascid- 

 ian and amphibian larvae, their fundamental chordate charac- 

 ters excepted, is superficial and disappears Vvdth any but the 

 most casual comparison of either their form, structure, or 

 activities. 



The tadpole larva of Amaroucium, at the period of its com- 

 plete development, has a total length of approximately 2.25 mm. 

 The body portion varies in length from 0.74 to 0.78 nmi. in 

 depth from 0.36 to 0.44 mm. and in width from 0.31 to 0.37 mm. 



TUNIC 



The body and tail proper of the tadpole are enveloped by a 

 comparatively thick, non-cellular tunic of a glassy, translucent 

 appearance. In the living tadpole the tunic is flecked at its 

 outer surface with numerous whitish points, the nuclei of the 

 flattened test-cells which form a delicate pavement epithelium 

 over its external surface. 



The cytoplasm of test-cells in general is homogeneous in 

 appearance, but it is not uncommon to find cells which contain 

 numerous yellowish bodies or are filled with reddish-orange 

 pigment granules. The quantity of pigment present in test- 



