642 



INVEIiTEBEATA 



CHAP. 



evagination of the parent ectoderm, the inner arises as an evaginaUon 

 of the parent atrial eavity (Fig. 46*7). No epicardia exist in the 

 Botryllidae. The young " oozooid " produced from the egg perishes 

 after having given rise to the first buds, which then give rise to the 

 rest of the colony (Fig. 467). 



Finally, in the family Diplosomidae we have a most extraordinary 

 conditionof affairs, which has been elucidated by the researches of Pizon 

 (1905). Budding begins by the development of epicardia in the embryo, 

 before the larva escapes from the egg-membrane. During the larval 



Fig. 467. — Bud of a Botryllid almost completely developed aud bearing two youug buds ; 

 seen from the dorsal side. (After Hjbrt. ) 



ai.c, atrial cavity ; &, young bud rudiment ; e.l, external layer of young bud rudiment ; g.s, gill-slits ; 

 H, heart ; i.l^ internal layer of young bud rudiment— this is seen to be a prolongation of the lining of the 

 atrial cavity of the mother ; iui, intestine ; m, mouth ; u.t, nerve tube (including hypophysial tube) ; ov, 

 ovary ; per, pericardium. 



life a perfect blastozooid is produced, so that the tailed larva possesses 

 two branchial sacs, two intestines, and two nervous systems, hut only 

 one notochord. One of the nervous systems, i.e. of the blastozooid, is 

 devoid of a sense-vesicle. When the larva fixes itself budding 

 continues in both blastozooid and oozooid. The epicardial stolon, 

 however, produces only a pharynx, nervous system, and the r-udiment 

 of an oesophagus. This oesophagus, instead of developing a new gut, 

 joins the oesophagus of the parent. At the same time an independent 

 bud is produced as an evagination of the rectum (Fig. 468, B), and 

 forms a new rectum though still retaining its connection with the 

 old one. 



Then one of two things may happen. Either a new stomach and 



