496 



TUNICATA. 



in the other Tunicates as the entodermal, endostylic, or epicardml 

 process. Between the ectoderm and the entoderm of the stolon, the 

 primary body-cavity extends, being directly connected with that of 

 the parent. In it we find an accumulation of mesoderm-cells (m) 

 completely enveloping the entoderm-process ; these, according to 

 SEELIGEB, are produced by the simple immigration of mesenchyme- 

 cells from the parent. Such cells (mz) are found in large numbers 

 at the point of origin of the stolon in the neighbourhood of the 

 elaeoblast-tissue. 



While SBELIGER considers that the mesoderm of the stolon results from 

 the immigration of a large number of mesenchyme-cells, TODABO (No. 107) 

 regards it as arising from the division of certain large germ-cells (germoblasts) 

 derived from the placental membrane (membrana germoblastoca, p. 435) at 



FIG. 264. Three transverse sections through the stolon of Salpa democratica-mucro- 

 nata at consecutive stages of development, c, peribranchial (cloacal) strands ; ec, 

 ectoderm ; en, entoderm-tube ; g, genital strand ; h, rudiment of testis ; mz, mesen- 

 chyme-cell ; n, neural tube ; o, upper blood-sinus ; ov, ovarian rudiment ; u, lower 

 blood-sinus. 



the cleavage of the original egg which gave rise to the solitary form. Since, 

 according to TODARO, the whole bud is derived exclusively from the descend- 

 ants of these cells, the ectoderm and entoderm of the stolon taking no part in 

 the formation of the buds, these latter are to be traced back to a form of 

 sexual reproduction. TODARO regarded the buds (in Salpa-chains) as younger 

 members of the generation to which the solitary form belongs. 



Transverse sections through older stolons (Fig. 264) reveal a condi 

 tion deviating somewhat from that above described, but showing- 

 great agreement with the stolon of Pyrosoma (Fig. 257, p. 490). In 

 the primary body-cavity, four regularly-arranged strands hate 

 appeared. The uppermost of these, which we will call the neural 

 strand or neural tube (Fig. 264, n) contains a distinct lumen. The 

 paired lateral strands also (c) are said by authors to have lumina 



