REPORT ON THE TUNICATA. 49 



In the Molgulidse there is a well-developed glandular mass, usually divided into 

 several lobes, which, in the absence of definite information as to its function, may be 

 called a liver. A similar organ is found coating the stomach in many of the Cynthiidse, 

 and in other forms, and in some of the Ascidiiche and sonic Ascidia.' Composite there are 

 thickenings of the wall of the stomach, which are possibly a less developed form of the 

 same organ. 



In many other cases, including Simple and Compound Ascidians, and also Sod/pa, 

 Doliolum, and Pyrosoma, there is present a system of fine tubules ramifying over the 

 stomach and part of the intestine. The tubules in all cases are colourless and highly 

 refracting, branch dichotomously, and unite into one or two larger tubes, which open into 

 the pyloric end of the stomach, or the first portion of the intestine. 



This organ has been known since the time of Savigny, and has been considered by 

 some authors as a liver, by some as a system of lacteals, and by others as part of the 

 circulatory apparatus. In some cases (some species of Salpa) a simple network of tubules 

 is formed by the dichotomous branching of the main duct, the twigs anastomosing freely. 

 In other cases (Salpa, Pyrosoma, Ascidia) a similar network is formed, but all the twigs 

 terminate in pyriform enlargements or ampullae, which are scattered over the meshes and 

 give a characteristic appearance to the system. In other forms again (Ascidia., Clavelina, 

 Perophora, and various Compound Ascidians) the tubules do not anastomose, but merely 

 branch freely and finally end in ampullae. Chandelon (1875) examined this organ 

 minutely in Perophora, and found that the walls of the tubules were formed of a single 

 layer of cubical or low columnar cells, placed upon an apparently structureless basement 

 membrane. The cells are distinctly nucleated and sometimes granular, and bear short 

 cilia projecting into the lumen of the tubule. He also found that the terminal ampullae 

 frequently contain highly refracting rounded concretions. 



The function of this system is still rather enigmatical. Chandelon considers that it is 

 neither renal nor hepatic, but that it must be considered as a digestive gland, secreting a 

 clear fluid which flows into the intestine, but the exact action of which is at present 

 unknown. 



Renal Organs. 



Several different organs have been recognised in the Tunicata as having a renal 

 function. In the Molgulidae there is a sacdike, usually sausage-shaped organ (PI. IV. 

 fig. 7, r.o.), lying on the inner side of the mantle on the right side of the body, posterior 

 to the genital mass of that side, and separated by the lining membrane from the peri- 

 branchial cavity. It lies alongside the pericardium in its entire extent, and undoubtedly 

 eliminates waste products from the blood. These are not expelled from the body, but are 

 stored up in the form of usually rounded or nodulated concretions which, as was first 

 shown by Kupffer in 1872, contain uric acid. Huxley (Manual of the Invertebrata, 1877) 



