SALl'A DEVELOPMENT OF THE STOLON. 



497 



round which the cells are arranged like an epithelium (Fig. 265, c), 



although Skelickk was not able t<> come to a definite conclusion on 

 this point. He called these strands the lateral strands, whereas the 

 other authors speak of them as the peribranchial, perithoracic or cloacal 

 tubes. They correspond to the peribranchial tubes in the stolon of 

 Pyrosoma. In the fourth, lower strand (</), young egg-cells early 

 appear, and it must therefore be called the genital strand. Besides 

 the^c strands, scattered tnesenehyine-eells are found in the primary 

 body-cavity ( Fig. 264, mz). 



In later stages of develop- 

 ment of the stolon (Figs. l'C.4 

 li and ('. 265), we find, 

 further, two large blood- 

 sinuses lined with an endo- 

 thelium, one lying above (o) 

 and the other below (u) the 

 entoderm-tube. Since tins 

 tube does not reach as far as 

 to the end of the stolon, com- 

 munication between the two 

 .sinuses is possible. At this 

 point the blood flows from 

 one sinus to the other. 



Another constituent ele- 

 ment of the stolon in Saljm 

 has been pointed ottt by 

 Bkooks, who found, on either 

 side of the stolon, between 

 the peribranchial tubes and 

 the ectoderm, another tube 



which, he considers, gives rise to the muscular system. These tubes 

 Brooks calls the mii*cnl<<r tubes (Fig. 265, m). 



In these six longitudinal strands running through the stolon we 

 have the rudiments of the most important organs of the buds. The 

 central entoderm-tube {en) yields the rudiment of the branchial sac 

 (pharynx) and of the alimentary canal; the neural tube yields the 

 ganglion and the ciliated pit, while from the peribranchial tubes (<) 

 the single atrial cavity arises, from the genital strand (//) the genital 

 organs, and from the muscle-tubes (m) the body-musculature, When, 

 later, through transverse constriction, the separate individuals (buds) 

 begin to detach themselves from the stolon, the longitudinal strands 



KK 



Fig. 265. — Transverse section through a young 

 stolon of Salpu (alter Brooks), c, peri- 

 bronchial tubes ; ec, ectoderm ; en, entoderm- 

 tube ; g, genital strand; m, muscle-tubes ; 

 //. neural tube ; ". upper, and /'. lower 

 biood-siuus. 



