46 ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA 



side of the partition and down on the other, the direction of the two 

 currents being generally, but not always, reversed with the reversal 

 of the general circulation. 



If the fcetuses be traced back upon this tube, it will be found that 

 towards the proximal end of the tube they lose their distinctive form 

 and become mere buds, processes of its wall, Plate XV. [Plate S] fig. 9. 

 It may thence be conveniently termed the "gemmiferous tube." 



24. The proximal extremity of the gemmiferous tube is simply 

 transversely striated, Plate XV. [Plate s] fig. 9 ; further on, two eleva- 

 tions become apparent on either side of the median line in each of 

 these stria;. These elevations are rudiments, the inner, of the nucleus, 

 the outer, of the ganglion of a fatal Salpa. Still more towards the 

 distal end of the tube, the young Salpce are much larger in proportion 

 to the tube ; the internal organs become marked, the heart becomes 

 visible by its contraction,s, and the body itself, although the respira- 

 tory apertures are as yet only marked out, not open, contracts occa- 

 sionally. Finally, the otolithes make their appearance, the body 

 becomes larger relatively to the nucleus and ganglion, and the 

 respiratory orifices open, Plate XVI. [Plate 6] figs, i, 2. 



25. The cavity of the gemmiferous tube communicates with the 

 dorsal sinus system of the foetus. Apparently the inner canal com- 

 municates by two canals, a wider and a narrower (Plate XVI. [Plate 6] 

 fig. i), with the anterior portion of the dorsal sinuses of the foetus, and 

 the outer canal communicates with the middle of the dorsal sinuses of 

 the foetus. However this may be, it is quite easy to watch the blood- 

 corpuscles of the parent making their way from the gemmiferous tube 

 into and out of the sinus system of the fcetuses. The writer has seen 

 one of the large blood-corpuscles of the parent entangled in the heart 

 (which was not more than -5^73 th of an inch long) of a very young fcetus. 



It is not exactly true that a gradual series in the development of 

 the fcetuses is to be traced along the gemmiferous tube. The tube is 

 rather marked out into sharply-defined lengths (generally three in 

 number), in each of which the fcetuses are nearly at the same stage of 

 growth, while they are much further developed than in the " length " 

 on the proximal side, much less advanced than in the " length " on 

 the distal side. 



26. In this species the young Salpa thus produced were extruded, 

 when fully developed, from the aperture mentioned in (22) ; but it 

 rarely happened that even two or three adhered together, and they 

 never formed the remarkable free-swimming chain of other species. 

 Generally they were found solitary, presenting only on their lateral 

 faces traces of their former adhesion. Those which were connected 



