SALPA DEVELOPMENT OF THE BUDS ON THE STOLON. 



503 



the individuals on the stolon of Salpa can be traced back to the 

 original nionoserial arrangement which is retained in the stolon of 

 Pyrosoma. 



Special interest attaches to the condition of individuals 3-7 of 

 Fig. 270, diagrammatically illustrated in Fig. 271. We can here 

 clearly see the relation of the buds to 

 the stolon. The stolon itself is cut 

 through obliquely, the section being 

 intermediate between a longitudinal and 

 a transverse section. We can see the 

 entoderm-tube of the stolon (en), an 

 teriorly, the upper blood-sinus (o) and 

 posteriorly the lower blood -sinus (u, cf. 

 Figs. 264 and 265). In individual 5, 

 we can trace the connection between the 

 right (rb) and the left (Ib) halves of the 

 branchial sac with the entodenn-tube 

 (en) of the stolon. All the other indi- 

 viduals are cut through at a different 

 level. In individuals 4 and 6, for 

 instance, the two blood-sinuses are inter- 

 calated between the right and left halves 

 of the respiratory cavity. 



We have reproduced other diagrams 

 by BROOKS (Figs. 272 and 273) which 

 still further illustrate this condition. 

 Fig. 272 gives the upper or oral aspect of 

 a stolon as it would appear if the primary 

 position of the buds had been retained 

 unaltered (cf. Fig. 268). The right half 

 of each bud is seen to have arisen from 

 the right side of the stolon and the left 

 half of the bud from the left side of the 

 stolon. Fig. 273 shows the buds shifted 

 alternately to the two sides of the stolon, 

 a condition attained through the repeti- 

 tion of the process taking place in indi- 

 vidual 5 in Figs. 270 and 271. The 

 buds 1, 3 and 5 have moved toward the 



right side of the stolon while 2, 4 and 6 have moved toward the 

 left side. The rotation of the individuals, however, is not yet visible. 



FIG. 272. Diagram of a stolon 

 of Salpa as it would appear 

 if no secondary shifting of 

 the individuals were to take 

 place (after BROOKS). P, 

 proximal; D, distal; R, 

 right ; L, left of the stolon ; 

 r and I, right and left sides 

 of the individuals ; es, endo- 

 style-folds ; n, ganglion. 



