AND DEVELOPMENT OF PYROSOMA. 
207 
The branchial stigmata just described are subdivided into quadrate meshes by some 
fifteen longitudinal bars which lie altogether on the inner side of the vertical ones, to 
which they are attached by their outer edges, projecting like so many narrow shelves into 
the pharyngeal cavity, and, as I observed in my earlier memoir on this animal*, are devoid 
of cilia. They terminate abruptly at their anterior and posterior ends, and they do not 
exhibit the small denticulations along their free edges which I have described in P. atlan- 
tlcum. The water taken in by the oral aperture must pass with perfect ease t hrough t hese 
meshes, and then, impelled by the cilia on the vertical branchial bars, make its way 
through the lateral atria and, on each side of the intestine, to the mid-atrium, whence ii 
finds an exit by the -atrial aperture. 
As to the proper digestive canal, the wide aperture of the oesophagus lies at the posterior, 
neural, angle of the pharyngo-branchial sac, and has an irregular figure ; but whether this 
irregularity is normal, or arises from the collapse of its walls after death, I cannot say. 
The oesophagus narrows as it passes back, and then curves sharply round towards the 
haemal side, to open, after a very short course, into the large oval stomach, which lies im- 
mediately behind the middle of the branchial sac, invested, everywhere but in front, by tin 
atrial tunic, and bathed in the blood which lies between it and iliat tunic. At its pyloric 
end it gives rise to the narrow commencement of the intestine, which, after suddenly 
dilating and turning forwards and to the luemal side, bends back sharply upon itself, and 
passing backwards to the neural side and to the right, ends opposite the middle oi" 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 tin- 
intestine, and eventually open by a single duct into the stomach. I have asked (I. c. p. 570) 
does this tubular system represent a hepatic 
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 giganteum 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 
Phallusia-f, and I have since t found an organ of the same nature in Phalkma, Cynthia, 
Molgula, Perophora, Botrylliis, Potrylloides, Clavelina, ApUdUm, Didemmm, and, in- 
deed, in all genera of Ascidians which have come under my notice, except Append icvlana. 
In some species of Didemnum, I have observed that the duct dilates almost at once into 
a large spheroidal sac. I suspect that Savigny was the original discoverer of tins system 
(see his memoir on Viazona, I. c. p. 176, and the description of pi. 12) The existence ol 
these tubuli in Salpa, Doliolum, and Pyrosoma has been confirmed by all subsequent 
observers. M. Vogt, however {I. c. 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 concur. 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 In 
* Loc. ciL pi. 17. fig. 3, and p. 583, line 4, where the word « sinus ' should be 
ones. 
t u Ueber die Entwickelung 
X See Reports of the British 
