POLYZOA AND TUNIC ATA. 



167 



FIG. 383. 



(Fig. 384), instead of being included in a common investment; so that 

 their relation to each other is very nearly the same as that of the poly- 

 pides of Laguncula ( 549), the chief difference being that a regular 

 circulation takes place through the stolon in the one case, such as has no 

 existence in the other. A better opportunity of studying the living 

 actions of the Ascidians can scarcely be found, than that which is afforded 

 by the genus Perophora, first discovered by Mr, Lister; which occurs not 

 unfrequently on the south 

 coast of England and in the 

 Irish Sea, living attached to 

 Sea-weeds, and looking like 

 an assemblage of minute 

 globules of jelly, dotted with 

 orange and brown, and link- 

 ed by a silvery winding 

 thread. The isolation of the 

 body of each zooid from that 

 of its fellows, and the ex- 

 treme transparence of its 

 tunics, not only enable the 

 movements of the fluid with- 

 in the body to be distinctly 

 discerned, but also allow the 

 action of the cilia that bor- 

 der the slits of the respiratory 

 sac to be clearly made out. 

 This sac is perforated with 

 four rows of narrow oval 



, through which a portion of the water that enters its oral 

 ) escapes into the space between the sac and the mantle, and is 



FIG. 3S4. 



Botryllus violaceus: A, cluster on the surface of a 

 Fucus: B, portion of the same enlarged. 



opemn 

 orifice 



^A, Group of Perophora (enlarged), growing from a common stalk: B, single Perophora; a, test; 

 6, inner sac; c, branchial sac, attached to the inner sac along the line c' c' ; e e, finger-like processes 

 projecting inwards; /, cavity between test and internal coat; /', anal orifice or funnel; a, oral ori- 

 fice; gr', oral tentacula; h, downward stream of food; h', oesophagus- i, stomach; fc, vent; I, 

 ovary (?) ; n, vessels connecting the circulation in the body with that in the stalk. 



thus discharged immediately by the annal funnel (/). "Whatever little 



