ASCIDI.E COMPOSITE. 101 



The latter, or social Ascidians, are placed on branched root-processes, 

 and have for a time, or permanently, a common circulation. The 

 mantle-parenchyma is usually of transparent hyaline consistency. 

 The body of the solitary Ascidians is far larger and is surrounded 

 by a hard cartilaginous, very thick and usually completely opaque 

 mantle, the surface of which often has wart-like protuberances and 

 incrustations of various kinds (fig. 560). 



Fam. Clavellinidae. Social Ascidians, the stalked individuals of which arise 

 from a common branched stolon, or on a common stem. The body is sometimes 

 (Clavellina) divided into three regions, like that of the Polyclinidce. Clavellina 

 Sav. ; Cl. lepadiformis Sav., North Sea ; Peropliora Listcri Wiegm., North Sea. 



Fam. Ascidiadae. Solitary Ascidians, usually of considerable size. The 

 individuals reproduce themselves, as it seems, only occasionally by budding, 

 and are connected, when they are aggregated together, neither by a common 

 mantle covering nor by bloodvessels. Ascidia L. (Phallusla Sav.) ; A. mam- 

 millata Cuv., Mediterranean; A. (Ciona) intestinalis L., etc.; Cynthia Sav., 

 C. papillosa Sav., C. microcosmus Cuv., Chevrenlitis Lac-Duth., Mediter- 

 ranean. 



The deep-sea Ascidians are very remarkable aberrant forms. Hypobythius 

 calcycodes Mos., and Octacnemits tythius Mos. 



Order 3. ASCIDI.E COMPOSITE.* 



Numerous individuals lie in a common mantle layer, and form 

 soft, brightly-coloured colonies, which have a spongy or lobed form, 

 and not unfrequently form crusts round foreign objects. 



In almost all cases the individuals are grouped in a definite number 

 round a common cloaca (Botryllidce), so that round or star-shaped 

 systems with central openings are formed in the colony (fig. 561). 

 The body is sometimes simple and short, sometimes long and divided 

 into two or three regions, and sends out branched processes contain- 

 ing blood into the common mantle mass, so that the latter is per- 

 meated by vascular canals. 



Fam. Botryllidae. The viscera of the simple body, which is not divided into 

 thorax and abdomen, lie by the side of the respiratory cavity ; without lobes 

 round the inhalent opening. Botryllus stellatus, Pall. ; B. violaceus Edw. 



Fam. Didemnidae. The viscera are for the most part placed behind the re- 

 spiratory cavity, and the body is divided into two parts, the thorax and abdo- 

 men. Didemnuin Sav. ; D. candidum Sav. ; D. styliferum Kow. 



Fam. Polyclinidae. The body of the individual is much elongated, and is 



* Besides Savigny, cf. M. Edwards, " Observations sur les Ascidies compo- 

 ees des cotes de la Manche." Mem. Acad. sc.. Tom. XVIII.. Paris, 1842. 



A. Giard, " Recherches sur les Synascidies." Arch, de Zool. exper., Tom. I., 

 Paris, 1872. 



K' walevski, " Ueber die Knospung der Ascidien." Arch, fur mikr. Anat., 

 Taf. X., 1874. 



