MOLLUSCA. 



195 



Young Tunicata swim, like tadpoles, by a tail, which 

 contains a peculiar rod-like body, consisting of nucleated 



FIG. 94. A. Group of Perophora, (enlarged,) growing from a common stalk : B. Sin- 

 gle Perophora. a. Test. b. Inner sac. c. Branchial sac, attached to the inner sac 

 along the line c' . c' . e. e. Finger-like processes projecting inward, f. Cavity between 

 test and internal coat, f . Anal orifice or funnel, g. Oral orifice, g* '. Oral tentacula. 

 h. Downward stream of food, h' '. OZsophagus. i. Stomach, k. Vent. /. Ovary. (?) 

 n. Vessels connecting the circulation in the body with that in the stalk. 



FIG. 95. Botryllus violaceus : A. Cluster on the surface of a Fucus. B. Portion of 

 the same enlarged. 



cells like the chorda dorsalis, or notochord ; an elongated 

 mass of cells in the Vertebrate embryo, which is after- 



