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 



remarkable combinations of the various halves of the body are 



produced. 



FIG. 233. Late stage in the budding 

 of Trididemnutn(&ftQT BELLA 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 ; m, stomach ; n, ganglion ; 

 oe, oesophagus ; r, rectum. 



FIG 234 Abnormal forms resulting from the development of one half of the bud in 

 Trididemnum (after BELLA VALLE, simplified). A, two branchial regions connected 

 with one intestinal loop ; B, two intestinal loops connected with one branchial 

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

 ganglion ; oe, oesophagus ; r, rectum. 



