574 
MR. HUXLEY ON THE ANATOMY OF SALPA AND PYROSOMA. 
Plate XV. fig. 9 ; further on, two elevations become apparent on either side of the 
median line in each of these striae. These elevations are rudiments, the inner, of the 
nucleus, the outer, of the ganglion of a foetal 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 contractions, and 
the body itself, although the respiratory apertures are as yet only marked out, not 
open, contracts occasionally. Finally, the otolithes make their appearance, the body 
becomes larger relatively to the nucleus and ganglion, and the respiratory orifices 
open, Plate XVI, figs. 1 , 2 . 
25. The cavity of the gemmiferous tube communicates with the dorsal sinus system 
of the foetus. Apparently the inner canal communicates by two canals, a wider and 
a narrower (Plate XVI. fig. 1 ), 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 foetuses. The writer has seen one of the large blood-corpuscles of the parent 
entangled in the heart (which was not more than 5 -^th of an inch long) of a very 
young foetus. 
It is not exactly true that a gr'adual series in the development of the foetuses 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 foetuses 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 Salpce 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 adhered 
together in a single series, the left antero-lateral extremity of the one being applied 
to the right postero-lateral extremity of the other ; and when they became free the 
traces of the connection were visible as angular processes of the sinus system. 
It is not correct to say that the Salpa chains have organs of attachment. ^ At 
first they are attached by the whole length of their lateral faces, the sinus system of 
one being continuous by a wide channel with the sinus system of the other ; but as 
they grow these communicating channels become more and more narrowed until 
they are mere points of connection ; all communication then ceases, and the Salpce 
become free from one another and move about independently, 
27. Having thus determined the nature and relations of the Salpa chain, it remains 
only to be said, that the young when freed, have a sub-ovoid, posteriorly-pointed form, 
five muscular bands, facetted sides, and in short are identical in form, and ultimately 
