74 



ASCIDIAXS 



CHAP. 



little or no food-yolk, and the tailed larvae (Figs. 26, 42, A) are 

 of the typical form and structure described in Chapter II. 



Fam. 3. Cynthiidae. Solitary fixed Ascidians (Fig. 39), 

 sometimes occurring in aggregations, but never forming colonies ; 

 usually with leathery or fibrous, opaque test, which is sometimes 

 encrusted with sand ; branchial and atrial apertures usually both 

 four-lobed. Branchial sac longitudinally folded (Fig. 36, A); 

 stigmata straight; tentacles simple or compound (Fig. 37); 



Br.f.l: 



D. 



"--end- 



-end.- 



FIG. 36. Diagrammatic trausver.se sections of branchial sacs of Cynthiidae. A, Cynthia ; 

 B, Styela ; C, Styelopsis ; D, Pelonaia. Br.f 1-7, First to seventh branchial fold ; 

 d.l, dorsal lamina ; end, endostyle ; mh, meshes. 



neural gland dorsal to ganglion ; gonads attached to body-wall. 

 This family is divided into three sections : 



Sub-Fam. 1. Styelinae. Not more than four folds (Fig. 36, 

 B) on each side of branchial sac; tentacles simple (Fig. 37, A). 

 The more important genera are Styela, Macleay, and Polycarpa, 

 Heller (Fig. 39), with stigmata normal; and Bathyoncus, Herd- 

 man, with stigmata absent or modified. There are a very large 

 number of species of both Styela and Polycarpa from all parts of 

 the world, including our own seas. A very abundant British 

 littoral form has been placed in an allied genus under the name 

 Styelopsis grossularia (Fig. 39, A). It is known in some places 

 round our coasts as " the red-currant squirter." This species has 

 only one well-marked fold in the branchial sac (Fig. 36, C). 

 Another exceptional British Styelid is Pelonaia corrugata, Forb. 

 and Goods. (Fig. 39, I), with no branchial folds (Fig. 36, D). 



