TUNICATA. 



1205 



' 



or tentacles, unless we except the peculiar 

 longitudinal row of tentacles passing forward 

 from the cesophageal aperture along the wall 

 of the branchial sac in Chclyosoma and other 

 genera. The oesophagus, sometimes obsolete, 

 is always very short, and is more or less pli- 

 cated longitudinally. 



The stomach is simple, generally merely a 

 slight dilatation of the alimentary tube (Jigs. 

 777. j, and 778. e). In A. mmnmillata it is 

 strongly plicated, and the pyloric extremity 

 narrowed by little fleshy papillae. It is some- 

 times bent upon the intestine and adherent to 

 it, and is often enveloped in the liver, with 

 which it is intimately adherent. Its walls are 

 very unequal, internally forming various la- 

 cunae, through which the bile penetrates, as in 

 the Bivalves ; the little bile-ducts are guarded 

 with valvules. In Boltenia renifonnis the sto- 

 mach is destitute of any internal folioles or 

 lacunae ; but in Ascidia intcstinalis, Cynthia 

 papillata, ~ C. canopus, and others, internal 

 plicae are present ; and in C. ampulla the sto- 

 mach is almost filled up with longish folioles, 

 and is of a light yellow colour from numerous 

 yellowish granules contained in its tissue. 



In Dendrodoa the stomach is striated ex- 

 ternally (fig. 778. e}. In Cystingia it is very 

 large, extending almost the whole length of 

 the body, and bears externally a deep longi- 

 tudinal depression, and is marked internally 

 with faint transverse striae. In Cynthia poly- 

 carpa and C. pomaria, a little ccecum occurs 

 just anterior to the pylorus. 



The intestine is usually short, simple, and 

 without coeca. In several species of Ascidia 

 its internal surface is traversed throughout 

 nearly its whole length by a semicylindrical, 

 hollow, ridgelike plication,*the " intestinal rib" 

 of Savigny, having the appearance of an inva- 

 ginated intestine. In its course, the intestine 

 generally makes one or two folds. Its walls 

 are thickened frequently by a glandular tissue, 

 probably supplying some fluid necessary to 

 digestion ; and its internal surface sometimes 

 bears biliary lacunae. The rectum leaving the 

 peritoneum floats unattached, and opens oppo- 

 site to the second or anal orifice of the mantle, 

 so that the excrements falling into the cloaca! 

 cavity are carried away by the current of 

 water leaving the body. In the stomach and 

 intestines is usually found a mass of finely 

 divided matter, chiefly, if not wholly, derived 

 from diatomaceous plants. Towards the 

 posterior extremity of the intestines the ex- 

 crements are usually moulded into little 

 earthy-looking filaments, as in most of the 

 Molluscs. The faeces appear to be formed 

 into these vermiform cords in the sulcus along 

 the side of the longitudinal intestinal fold. 



In A. mammillfita the duodenum has several 

 slight transverse striae. In Cynthia ampulla the 

 intestinal walls are internally hollowed into 

 lacunae and little folds, which, like the coats 

 of the stomach, pour out a yellowish fluid like 

 bile. In Dendrodoa the intestine is of con- 

 siderable length. In Boltenia renifonnis also 

 the intestine is long, mounting up as high as 

 the base of the pedicle, then descending nearly 



parallel with itself and terminating in an as- 

 cending conical rectum, the anus having a 

 scalloped margin. In this species there are 

 twelve subcubical bodies, separate from each 

 other, adherent to the upper and inner surface 

 of the rectum, having the free edge of a part 

 of the ovary between them and the liver. In 

 size they differ among themselves, the largest 

 lying towards the anus, and the smallest in 

 the opposite direction ; they have no apparent 

 communication either with the intestines, with 

 each other, or externally. Under the micro- 

 scope their structure appears to consist of a 

 very fine homogeneous colourless membrane, 

 enclosing an infinite number of excessively 

 minute nucleated cells, readily separable from 

 the tissue, which have much the appearance 

 of blood globules. In Chelyosoma the digestive 

 apparatus is large, and, from the shape of the 

 animal, is arranged flatwise. The oesophagus 

 commences at the posterior left corner of the 

 branchial sac, between the two chambers of 

 the heart. Advancing obliquely forwards, it 

 enters the stomach, around which are clus- 

 tered the biliary cceca. The intestine goes on 

 to make a single bend, and, coming back to 

 the left posterior corner, proceeds towards, 

 and terminates abruptly at a very short dis- 

 tance from, the anal orifice. 



The liver of the Ascidiadcc generally occurs 

 in a very degraded form ; it is either absent, 

 as in Ascidia, Dendrodoa, and some Cynthia, 

 or its place is supplied by lacunae and folioles 

 on the inner coats of the intestinal canal, oc- 

 curring, in Cynthia ampulla, both in the sto- 

 mach and duodenum ; or, on the other hand, 

 it is more or less amply developed, as in Bol- 

 tenia, where it appears as an irregularly tabu- 

 lated body, coating the stomach externally 

 behind the right ovary, and passing from the 

 lower extremity of the body, half-way up, in 

 the cavity of the mantle. The lobes differ in 

 size: the largest are placed towards the pyloric 

 or highest end of the stomach, and are more 

 distinctly separated from each other than the 

 smaller ones ; they are more or less rounded 

 and granulated, their surface being minutel} 

 papillated and composed of minute round 

 bodies, at first sight resembling ova. In Cyn- 

 thia the liver is greenish, granulated, foliated, 

 or, as in C. Dione, caniculate. It is sometimes 

 formed of clustered groups of flask-shaped 

 cellular bodies, the individual cells being fixed 

 by their larger ends, and having a radiate ar- 

 rangement. It is intimately adherent to the 

 external surface of the stomach, which fre- 

 quently is totally enveloped by it. The bile 

 enters the stomach by distinct holes at the 

 bottom of the cavities of the little lacunae 

 before-mentioned. In C. microcosmus, and 

 others, the liver is divided into masses, one of 

 which is situated on the left of the bran- 

 chial sac and quite free of the abdomen. The 

 liver in Ascidia in'cstinalis has the appearance 

 of somewhat salient glandular bodies, situated 

 as well on part of the intestine as on the sto- 

 mach. In Chelyosoma this organ is represented 

 by a cluster of short coecal tubes lying all over 

 the external surface of the stomach. The 

 4H 3 



