22 THE VOYAGE OF H.M.S. CHALLENGER. 



The nerve ganglion is placed at the anterior end of the branchial sac on the dorsal 

 edge (Fig. 4, n.g.). It has a small pigmented sense-organ placed upon it. The sub- 

 neural gland bears the usual relation to the ganglion, being on its ventral surface. The 

 gland has a duct leading forwards and ventrally to open into the posterior dorsal part 

 of the prebranchial zone on the dorsal tubercle. The aperture of the duct is simple, 

 but prominent (PL II. fig. 13). 



On each side of the anterior end of the branchial sac, close to the peripharyngeal 

 band, is seen a mass of rounded glandular cells (PI. I. figs. 18, 19, and 20), which have 

 given rise to a good deal of speculation. They were supposed by Savigny to be 

 laterally placed ovaries. This mistake was corrected by Huxley, who found the true 

 position of the ova. Huxley himself suggested that the cell masses were kidneys, and 

 Keferstein and Ehlers regarded them as being probably organs for aiding in the pro- 

 duction of buds. Panceri ' first showed that they are really organs for the production 

 of the phosphorescence, for which Pyrosoma is so famous. 



The alimentary canal is placed posteriorly to the branchial sac (Fig. 4). The 

 oesophageal opening is wide. It lies at the dorsal edge of the posterior end of the 

 branchial sac, and the oesophagus curves posteriorly and ventrally to open into the 

 dorsal end of the large quadrangular stomach. The stomach lies with its longer axis 

 directed dorso-ventrally. It is usually narrower at the intestinal than at the oesoph- 

 ageal end. The intestine is a narrow curved tube which runs at first ventrally, and 

 then curves anteriorly, then dorsally, and, finally, a little posteriorly, so as to describe 

 nearly a complete circle. The anus opens into the peribranchial cavity, which is a 

 large space consisting of three regions — (l) a median part occupying the posterior 

 part of the body, and opening into the common cloaca by means of the atrial aperture ; 

 and (2 and 3) two lateral parts extending anteriorly from the median part, one at 

 each side of the branchial sac. Into these lateral regions of the peribranchial cavity the 

 slits in the wall of the branchial sac open, while the anus opens into the median 

 posteriorly placed region. 



Eamifying over the wall of the intestine is found a system of delicate tubules which 

 branch and anastomose, and finally end in small ampulla3. This, like the corresponding 

 systems in other Tunicata, is probably a digestive gland. It pours its secretion by a 

 common duct into the pyloric or ventral end of the stomach on its anterior border. 



The heart is situated near the posterior end of the endostylc ; and close to it, and 

 therefore placed posteriorly and ventrally, there is a diverticulum of the body wall 

 containing a process from the endoderm. This structure is the gemmiparous stolon 

 upon which the buds destined to become the future Ascidiozooids of the same colony 

 are produced. This stolon is evidently identical both in constitution and in position 

 with the various ijrocesses for the production of buds found in the Compound 



1 Alii Accad. Sci. Fis. e Mat. Napoli, vol. v., no. 13. 



