29 



colonies, a continuity of adjacent pellucidum lobules can usually 

 be made out, but such continuity between adjacent lobules of the 

 pellucidum and constellatum types is significantly wanting. 



OS. 



p as. 



ep t •• 



ad p. ty. 



t. o.s. p. as. m. 



Fig. 1. — Outline sketches of the body portion of the tadpole larvae of A. pellucidum (A) 

 and A. constellatum (B), drawn to scale with the camera lucida, as seen from the right side, 

 to show differences in size and structure, o.s., atrial siphon; ad.p., adhesive papillae; ep.t., 

 epidermal tubes; m., mantle; m.c.b., muscle-cell bands; n., notocord; o.s., oral siphon; p., 

 pigment spots in sensory vesicle; per., pericardium; t., tunic; t.v., test vesicles. 



A considerable number of characters in which there is diversity 

 between the two species are enumerated and contrasted in parallel 

 columns in the tables which follow. Table 1 lists characters 

 peculiar to the larval form. These characters, as differentiated 

 in the larva of A. constellatum, have been described and discussed 

 in two papers (Grave, 1920, 1921). The activities and structures 

 of the tadpole larva of A. pellucidum form the subject of a paper 

 now in the course of preparation. Table 2 lists characters of the 

 adult colony or ascidio-zooids, as compiled from data published by 

 Verrill, Van Name, and Sumner, Osburn and Cole. In addition to 

 the characters of the two species, enumerated in Table 2, I have 



