34 



ZOOLOGY 



SECT. 



become constricted off, and in the form of little groups of cells, 

 each consisting of seven strings of cells with an ectodermal 

 investment, creep over the surface of the parent (Fig. 693, c, 

 and Fig. 694) till they reach the dorsal stolon, to which they 



FIG. 692. Doliolum, late stage in the development of the tailed larva, atr. ap. atrial aperture ; 

 dors. st. dorsal stolon ; end. endostylc ; lit. heart ; ne. gn. nerve-ganglion ; noto. notochord ; 

 or. ap. oral aperture ; vent. st. ventral stolon. (After Uljanin.) 



become attached. The dorsal stolon soon becomes elongated, and 

 the bud-like bodies attached to it multiply by division and deve- 

 lop into zooids. As the long chain of zooids thus established 

 becomes farther developed, the parent Doliolum (Fig. 694) loses 

 its branchias, its endostyle and its alimentary canal ; at the same 



ne. 



dors.st 



or.ap 



vent. si 



FIG. 693. Doliolum, lateral view of asexual stage, showing the early development of the buds. 

 atr. ap. atrial aperture ; dors, st. dorsal stolon ; e. embryos passing over the surface from the 

 ventral stolon to the dorsal ; hi. heart ; ne. gn. nerve-ganglion ; or. ap. oral aperture ; vent. st. 

 ventral stolon. (After Uljanin.) 



time the muscle-bands increase in thickness, and the nervous 

 system attains a higher development, until the whole parent 

 comes to resemble, in a certain sense, the nectocalyx of a Siphono- 

 phore (Vol. I. p. 147), its exclusive function being by its contrac- 

 tions to propel the colony through the water. 



