3:2 



PHYLUM TUNICATA (iJROCHORDA). 



other, saddle-shaped, becomes the atrium of the bud. The organs aie 

 formed in the usual way, the pericardium and intestine as outgrowths of 



the pharynx and the 

 nervous system from 

 the endoderm. The 

 original connection re- 

 mains throughout life 

 ...Ed a s the vascular ecto- 

 dermal tube referred 

 to above. 



Botryllus Gartner 

 and Pallas (Fig. 23), 

 colony thin, encrust- 

 ing, systems circular, 

 gonads paired, placed 

 laterally, littoral, Eur., 

 Med., N. Amer. Poly- 

 cyclus Lamarck, as 

 last, but colony thick 

 and fleshy, Eur. and 

 Med. Botrylloides H. 

 Milne - Edw., colony 

 thin encrusting, sys- 

 tems elongated or 

 branched irregularly, 

 gonads paired, lateral. 

 Sarcobotr ylloides v. 

 Symplegma Herdman, 



cm. 



FlG. 24:. Diagram of a dorsal view of a young oozoid or of a 

 bud of Botryllus violaceus (after Pizon, from Perrier). B fu- 

 ture mouth ; bl rudiment of new blasto-zooid of one side ; 

 c.vib vibratile tube ; ect ectoderm ; gh gonad ; i intestine ; 

 perb peribranchial sac (atrial cavity) ; pv epicardical di- 

 verticulum ; vb pharynx ; Vd cloacal part of future atrial 

 cavity. 



Drasche, like last, but colony thick and fleshy. 



colony stalked, gonads unpaired, in intestinal loop, Bermuda. 



Fam. 2. Distomidae. Colony rounded or massive, rarely encrusting, 

 either sessile or with long peduncle ; systems irregular, inconspicuous or 

 absent, both mouth and atrium usually opening on 

 the surface of the colony. Zooids divided into thorax 

 and abdomen, and sometimes provided with long vas- 

 cular ectodermal appendages ; test gelatinous or cartila- 

 ginous, sometimes with non-stellate calcareous spicules ; 

 pharynx without internal longitudinal bars ; dorsal 

 lamina as languets ; gonads and heart in or alongside 

 intestinal loop, spermatic vesicles numerous, vas de- 

 ferens straight. 



In the Distomidae the budding is epicardial. The 

 epicardium arises as a pair of diverticula of the 

 pharynx, one on each side of the oesophagus. The right 

 of these detaches a pericardium, then separates from 

 the pharynx and becomes connected to the left tube to 

 form the definite epicardial tube. This pushes out the 

 ectoderm and forms a ventral stolon, which buds off 

 small free bodies into the test ; these may multiply 

 by fission and eventually develop into new zooids.* 

 In Colella some of the buds, those placed in the deeper 

 parts of the stalk, have a store of reserve food material in their ectoderm. 



G. 25. Distaplia 

 (after Herdman 

 from Delage and 

 H6rouard). 



* Kowalevsky, op. cit. Julin, Int. Cong. Zoology, Leyden, 1896. 



