SALPA DEVELOPMENT OF THE STOLON. 



495 



Iii rt>i//><t /'i/mata, S. affinis and S. 

 straight and runs forward along the 

 runcinata-fusiformM and costata- 

 yY/rx//, it at first runs forward on 

 the ventral side, but then bends 

 round and runs backward on the 

 left side of the nucleus, and only 

 passes out behind this organ. In 

 S. democratica - mucronata, 8. 

 scutigera - confederate, and S. 

 cordiformis - zonaria, the stolon 

 winds spirally round the nucleus 

 (Fig. 262). 



The individual buds here, as in 

 Pi/i-oMHim, become marked off by 

 transverse constrictions which 

 appear on the stolon. While, 

 however, in Pyrosoma, the separate 

 parts of the stolon remain in a 

 Dingle row, in the Salpidae, 

 secondary shifting leads to a bi- 

 serial arrangement. A large 

 number of buds consequently can 

 of the stolon. 



dolichosama, it is more or less 

 ventral side of the body. In S. 



FIG. 262. Posterior end of the body in 

 a solitary form of tfalpa democratica- 

 mucronata, from the dorsal side (after 

 LEUCKART). d, alimentary canal ; h, 

 brood-cavity ; o, aperture of the same ; 

 st, proliferating stolon. 



be crowded on to a short piece 



A. Structure and Development of the Proliferating Stolon. 



Our knowledge of the earliest stages of the development of the 

 stolon is due chiefly to SEELIGER (No. 105). The stolon, as already 

 mentioned, is at first a small, conical 

 outgrowth on the left side of the 

 body near the posterior end of the 

 endostyle. Three layers can be dis- 

 tinguished in it ; ectoderm, mesoderm 

 and entoderm. The ectoderm of the 

 stolon passes direct into that of the 

 parent. The entoderm-sac of the 

 stolon (Fig. 263, en) is a diverticulum 

 of the wall of the parent's branchial 

 sac arising immediately behind the 

 endostyle. This diverticulum exactly corresponds to the organ known 



FIG. 263^ Youngest stage of de- 

 velopment of the stolon in Salpa 

 (after SEELIGER). b, blood-sinus ; 

 ec, ectoderm ; en, entoderm- 

 process ; m, mesoderm ; mz, 

 mesenchyme-cells. 



