462 



TUNICATA. 



The thoracic and the abdominal buds do not always develop equally. 

 In some cases only the abdominal bud develops. This leads to an 



abnormality, consisting of one 

 branchial region with two fully 

 developed intestinal loops (Fig. 

 234 B). In such cases the intestine 

 of the parent may degenerate later. 

 This condition is regarded by Della 

 Valle as a rejuvenescence, and 

 consists in the development of an 

 individual, the anterior half of which 

 belongs to the parent, while its 

 posterior half develops anew (see 

 also Oka, No. 646). A similar 

 process may occur in the anterior 

 part of the body, when the thoracic 

 bud alone develops (Fig. 234 A). 

 The process is often still further 

 complicated by the appearance of 

 the bud-rudiments of a third genera- 

 tion arising from the not yet fully 

 developed bud. In this way 

 le various halves of the body are 



Fin. 233. —Late stage in tlie budding 

 of Tridide?nnu>n(a,fter Della Valle). 

 The alimentary canal of the perfectly 

 developed bud still remains connected 

 with that of the parent, e, atrial 

 aperture; en, endostyle; i, branchial 

 aperture; in, stomach; n, ganglion; 

 lie, oesophagus ; r, rectum. 



remarkable 

 produced. 



combinations of tl 



Pig. 234. — Abnormal forms resulting from the development of one hajf of the bud in 

 Trididemnum (alter Della Valle, simplified). A, two branchial regions connected 

 with one intestinal Loop; H. two intestinal loops connected with one branchial 

 region, e, atrial aperture; en, endostyle; i, branchial aperture; m, stomach; n, 

 ganglion ; oe, oesophagus; r, rectum. 



