506 



TUNICATA. 



as a continuous tube in which we recognise the remains of the stolon 

 (Fig. 276 G). 



Even in later stages, the two principal blood-sinuses (Figs. 264, 275, 

 o and u) which appeared at an early stage within the developing 

 stolon (Fig. 264 B) are still to be found in the remains of that 

 structure. These vessels are bounded by distinct epithelial walls and 

 have no connection with the bud, the blood-vascular system of which 

 arises quite independently. The blood from the body of the parent 

 therefore does not pass over into the body of the bud. 



Fig. 275. — Transverse section through a stolon of Salpa (after Salensky). .1, with 

 younger, and B, with older buds, cl, atrium ; d, enteric canal ; e, atrial aperture ; 

 es, endostyle ; h, connecting process (couplings) ; k, gill ; n, nervous system ; o, 

 upper blood-sinus ; ov, ovary ; p, pericardial vesicle ; ph, pharynx ; st, remains of 

 stolon ; v, lower blood-sinus. 



When the buds are fully developed the remainder of the stolon 

 degenerates, breaking up into segments which are drawn in by the 

 buds and absorbed by them. The connection between these (the 

 individuals of the chain), originally brought about by the stolon, is 

 now maintained by means of integumental processes derived from 

 buds (the so-called connecting processes or couplings, Fig. 278, hf), 

 which originate as outgrowths of the integument. These processes 



