474 



TUNICATA. 



Oft 



in such a way that one pair becomes attached to each primitive bud as it 

 separates from the stolon (Fig. 252 A, p. 483). While these large, amoeboid 

 cells are attached to the surface of the primitive buds, they do not seem to 

 belong directly to the bud itself. According to BARROIS, they are modified 

 test-cells concerned in the transportation of the primitive buds. Similar cells 

 are found on the buds of Anchinia and the primitive buds of Dolcliinui. 



The median buds differ essentially from the lateral buds in form 

 and function. The lateral buds or gastrozooids (Fig. 244) are 

 asymmetrical, short-stalked individuals in which, through increase in 

 length, the characteristic barrel-shape disappears. They may be 

 likened to spoons with deep concavity and 

 short handle. The concavity of the spoon is 

 formed by the pharyngeal cavity with its 

 wide aperture, the dorsal wall being formed 

 by the somewhat swollen branchial lamella. 

 The atrial cavity of 'the bud and its aperture 

 are so dilated as altogether to disappear. 

 The gill-clefts therefore lead from the pharyn- 

 geal cavity direct to the exterior. The 

 alimentary canal (d) is well developed, the 

 muscle-hoops are vestigial, and the genital 

 rudiment found in the bud degenerates in 

 the further course of development. The 

 lateral buds are not able, after their detach- 

 ment from the dorsal outgrowth, to lead an 

 independent life, and they do not multiply in 

 any way. Their sole functions are the taking 

 in of food and respiration ; they obtain the 

 nutritive material for the other buds of the 

 dorsal outgrowth as well as for the blasto- 

 zooid (" nurse ") which has lost its alimentary 

 canal (p. 388). They correspond to the 

 nutritive polyps of a Siphonophoran stock (FoL) and have therefore 

 been called nutritive forms or trophozooids. 



The median buds (phorozooids), on the contrary, after attaining their 

 full development, become detached from the dorsal stolon of the first 

 " nurse " (blastozooid) generation and lead a free pelagic life. These 

 individuals (Fig. 245 B) in the development of their body, closely 

 resemble the barrel-shaped sexual generation, from which they are 

 only distinguished by the absence of the genital organs (which here 

 degenerate at an early period in the bud) and by the presence of ar 



FIG. 



244. --Lateral bud 

 (gastrozooid) of Dolio- 

 lum Miilleri (after 

 GBOBBEN). an, aual 

 aperture ; d, alimentary 

 canal ; es, endostyle ; 

 Jt, ciliated arch ; ks, 

 gill-clefts ; n, ganglion ; 

 p, pericardial vesicle 

 and heart; ph, pharynx. 



