332 ON THE ANATOMY AND DEVELOPMENT OF PYROSOMA 
and passing backwards to the neural side and to the right, ends 
opposite the middle of the stomach in the abruptly truncated anus, 
which opens into the atrium. 
In my memoirs on Salpa, Pyrosoma, and Doliolum, already referred 
to, I have described, in all these genera, a remarkable system of fine 
transparent tubes which ramify over the intestine, and eventually 
open by a single duct into the stomach. I have asked (/ ¢ p. 570), 
does this ¢wbular system represent a hepatic organ? or is it not more 
probably a sort of rudimentary lacteal system—a means of straining 
off the nutritive juices from the stomach into the blood by which 
these tubes are bathed? In Pyrosoma giganteui the duct of the 
system is very obvious, opening into the stomach in front of the origin 
of the intestine, and somewhat enlarged at its opposite end. 
Krohn has described the structure and development of a similar 
system of tubuli in Phal/usia, and I have since? found an organ of 
the same nature in Phallusia, Cynthia, Molgula, Perophora, Botryllus, 
Botrylloides, Clavelina, Aplidium, Didemnum, and, indeed, in all genera 
of Ascidians which have come under my notice, except Appendicu- 
faria, In some species of Dedemnum, 1 have observed that the duct 
dilates almost at once into a large spheroidal sac. I suspect that 
Savigny was the original discoverer of this system (see his memoir on 
Diazona, /. c. p. 176, and the description of pl. 12). The existence of 
these tubuli in Sal/pa, Doltolum, and Pyrosoma has been confirmed by 
all subsequent observers. M. Vogt, however (/. ¢ p. 31), affirms that 
the organ consists of solid branches, and that it partakes of the nature 
of a muscular organ, in neither of which opinions can I possibly con- 
cur. I have no doubt whatever that the apparatus is a glandular 
organ, and that it performs a part, at any rate, of the functions of a 
liver. 
The vascular system of Pyrosoma is exceedingly simple; nor 
could we anywhere find a more convincing example of the validity 
(in some cases, at any rate): of Milne-Edwards’s views of the 
circulation in the Mollusca than is offered by this animal. The heart 
lies close to, and apparently connected with, the right side of the 
posterior and heemal wall of the pharynx, between the endostyle and 
the bend of the intestine; and it appears to have exactly the same 
structure as in P. atlanticum. There are no vessels, the whole inter- 
space between the inner tunic and the outer, or between these and 
the atrial tunic, being one vast blood-sinus, with which the canals in 
the branchial bars communicate at each end. I have spoken of the 
1“ Ueber die Entwickelung der Ascidien,” Muller’s Archiy, 1852, p. 331. 
° See Reports of the British Association, 1852. 
