SYNASCIDIA. 



37 



Fam. 7. Polystyelidae. Colonies massive or encrusting, rarely stalked 

 or formed of small masses connected by stolons, without common cloacal 

 cavities ; both apertures 4-lobed, opening directly to the exterior ; pharynx 

 large, with strong internal longitudinal bars ; tentacles small, numerous ; 

 dorsal lamina as membrane ; intestine alongside pharynx, rarely extend- 

 ing behind it ; gonads as poly carps in mantle projecting into atrium ; gem- 

 mation doubtful, probably from vascular stolons ; in Goodsiria it is stated 

 to be pallial (Ritter). It is not certain that all the genera here included 

 have the power of budding, and it is possible that some of them are close 

 aggregations of simple Ascidians. By their structure they approach Poly- 

 car pa (Styelinae} of that group. Goodsiria Cunningham, Ohorizocormus 

 Herd., Oculinaria Gray, Thylacium Carus, Poly sty ela Giard, Synstyela 

 Giard. 



Fam. 8. Claveliniclae. The zooids are not embedded in a common test 

 but are attached to creeping stolons or to a stolonial mass from which 

 new ascidiozooids are formed by gemmation ; 

 test usually gelatinous, thin and transparent ; 

 pharynx often without internal longitudinal 

 bars, which are without papillae ; tentacles 

 simple, dorsal lamina as languets ; intestine 

 usually behind pharynx as abdomen ; gonads 

 in intestinal loop. This family comes closest 

 to the genus dona of the simple Ascidians, with 

 which group it is often united. 



The stolon of * the oozoite of Clavelina (form 

 produced from the egg) is divided into two 

 parts by a septum, the stolonic septum. This is 

 a collapsed continuation of the epicardium and 

 therefore contains endoderm. At the free end 

 of the stolon the septum ceases so that the cavi- 

 ties (blood spaces) on either side of it are in 

 communication. At the other end the septum 

 is continuous with the hind end of the single 

 epicardial tube (in the blastozooite with the 

 hind end of the pericardium, Fig. 29), the pos- 

 terior part of which is applied to the dorsal side of the pericardium, while 

 the front end forks to open by two openings into the hind, end of the 

 pharynx just ventral to the oesophagus. In the blastozooites or forms 

 which have been produced by budding (Fig. 29), the arrangement is the 

 same except that the stolonic septum is connected with the pericardium 

 and not with the epicardium ; but this is not a matter of any great 

 importance, inasmuch as the pericardium develops from the hind end of 

 the epicardium, with which it remains in close contact. The point is 

 that the stolonic septum is an endodermal structure continuous with 

 or developed from the pharyngeal wall. The form produced from the 

 egg remains asexual, the zooids (blastozooites) which are budded from the 

 stolon of this become sexual (Fig. 29). The budding takes place in this 

 way. The stolon produces on its upper side a small diverticulum (Fig. 31), 

 into which the septum sends a hollow endodermal prolongation. This 



FIG 



Diagrammatic 

 transverse section through 

 the posterior part of a bud 

 of Clavelina (from Kor- 

 schelt and Heider). ep 

 epicardium ; h heart ; 

 t intestine ; m stomach ; 

 n visceral nerve cord ; 

 pc pericardial vesicle. 



* Kowalevsky, Sur le bourgeonnement du Perophora listeri, Rev. Sci. 

 Nat. MontpeMier, 1874, and Ueb. d. Knospung d. Ascidien, Arch. f. Mik. 

 Anat., 10, 1874. 



