EXPLANATION OF THE PLATES. 



REFERENCE LETTERS. 



a. The closed end of the colony, 

 as. An ascidiozooid. 



b. The open end of the colony. 



c. The cloaca of the ascidiozooid. 

 CC. The common cloaca of the colony. 

 d. The mouth. 



f. The mantle of cellulose. 



g. The endostyle. 



h. The luminous organ. 



i. The testis. 



j. A bud. 



k. The stomach. 



1. The intestine. 



n. First oral muscle. 



o. Second oral muscle. 



p. The oesophagus. 



pa. 1. The primary ascidiozooid on the edge of the colony. 



pa. 2. The primary ascidiozooid on the side of the colony. 



FIGURES. 



F„ ; . i. — The cyathozooid and the four primary ascidiozooids of Dipleurosoma elliptica. 



Fig. 2.— A young colony of Dipleurosoma elliptica, with seven verticils of ascidiozooids 



Fig. 3. — Transverse section of the colony shown in figure 2. 



Fig. 4. — Side view of a fully grow n colony of Dipleurosoma elliptica. 



Fig. 5. — Edge view of same. 



Fig. (i. — The open end of same. 



Fig. 7. — Transverse section of same. 



Fig. S. — A single ascidiozooid from a fully grown colony of same. 



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