518 THE ANATOMY OF LXVERTEBRATED ANIMALS. 



the Botvyllidoe, however, the stomach is bent at right angles 

 upon the gullet, as in Appendicularia ; the intestine almost 

 immediately turns forward, and then, turning sharply upon- 

 itself, passes forward parallel with the hinder part of the 

 branchial sac, on one side of which it opens into the atrium. 



A similar arrangement obtains in Perophora, but the 

 branchial sac extends backward for a short distance on one 

 side of the stomach. In the solitary Ascidians the stomach 

 lies sometimes altogether behind tlfe branchial sac (Pelonaia, 

 some Phallusm) ; but, usually, the branchial sac extends so 

 far back that the whole alimentary canal lies on one, usually 

 the right, side of it. In Phallusia monachus, the hinder end 

 of the branchial sac is recurved, and the oesophageal opening 

 looks backward to the fundus of the sac, instead of forward 

 to the mouth. 



In many Ascidians a strong fold of the endoderm of the 

 intestine projects into its interior, as in Lamellibranchs and 

 in the Earthworm, where such a fold constitutes the so-called 

 typhlosole. 



In the pelagic Tunicates, Salpa, Pyrosoma, and Poliolum, 

 I found a system of fine tubules 1 which ramify over the in- 

 testine and are eventually gathered together into a duct which 

 terminates in the stomach. An apparatus of the same nature 

 exists in Phallusia, Cynthia, Molgula, Perophora, Botryllus, 

 Potrylloides, Clavelina, Aplidum, and Didemnum? and I 

 have little doubt that it is hepatic in its function. In some 

 Cynthice, however, there is a follicular liver of the ordinary 

 character, which opens into the stomach by several ducts. 



In some P/iallusice, the alimentary canal is coated by a 

 very peculiar tissue, consisting of innumerable spherical sacs 

 containing a yellow concretionary matter. In Molgula (and 

 in the Aseidia vitrea of Van Beneden) an oval sac containing 

 concretions lies close to the genital gland, on one side of the 

 body. As these concretions have been shown by Kupfer 3 to 

 contain uric acid, the organ must be regarded as renal in 



1 Savigny seems first to have observed this organ, as would appear from his 

 account 01 Diazona (" Memoires sur les Anhnaux sans vertebres," p. 176), and 

 the description of Plate 12. Lister mentions and figures it in Perophora (" Phil. 

 Trans.," 1834). 



2 " Reports of the British Association," 1852. Hancock, " On the Anatomy 

 and Physiology of the Tunicata." (" Journal of the Linnoaan Society," vol. ix.) 

 The development of these- tubules from the stomach was traced by Krohn in 

 Phallusia, and by myself in Pyrosoma. 



3 " Zin- Entwickelung der einfachen Ascidien." (" Archiv fur Mikr. Ana- 

 tomic," 1872.) 



