AND PHYSIOLOGY OF THE TUNICATA. 315 



well-known memoir in the ' Philosophical Transactions'*, "trans- 

 parent vessels" ramifying over the intestine; but he does not 

 appear to have observed the terminal vesicles, and the termina- 

 tion of the duct in the stomach, or he scarcely could have sup- 

 posed, as he did, that the vessels he described were lacteal s. 



With this exception, this peculiar form of the hepatic organ 

 seems entirely to have escaped notice until A, Krohn gave a 

 very good description of a similar structure in a paper " On the 

 Development of the Ascidians," published in MUller's Archiv, 

 1852-53 1- The species examined by this naturalist was Ascidia 

 mamillata ; and although he appears to have traced with great 

 accTiracy the development of the organ, he seems to have failed 

 in detecting the duct in the adult animal. Prom the general 

 chara.cters, however, obtained by his examination of the young 

 and adult combined, he is disposed to conclude that the " secre- 

 tion prepared in the caeca must be accessory to digestion ; but 

 whether or not the watery secretion is bile, and the gland there- 

 fore a liver," he concludes, " must for the present be left unde- 

 cided." Neyertheless, after the above description of the numerous 

 modifications of the organ, and particularly when the position of 

 the duct in relation to the alimentary tube is taken into account, 

 few physiologists will be inclined to doubt that this organ is a 

 true liver, though low and rudimentary in structure. 



The reproductive organs are well developed in the Tuuicates ; 

 and in all of them the two sexes are combined in the same in- 

 dividual, though the male and female elements are always 

 secreted by distinct organs, which, howeve'r, frequently compose 

 one or more compound masses that have the parts so intimately 

 united that careful examination is required to detect them ; hence 

 in several of the CynthiadcB the testis has been entirely over- 

 looked : the oviduct and vas deferens are likewise constantly 

 distinct. 



In Ascidia sordida, the ovary is composed of numerous tubular 

 branches, which ramify in a radiating manner over the left side 

 of the looped portion of the intestine. The oviduct passes 



* " Some Observations on the Structure and Functions of Tubular and Cel- 

 lular Polypi and of Ascidise," Phil. Trans. 1834, p. 380. 



t See ' Scientific Memoirs,' edited by Henfrey and Huxley, p. 328. Before 

 I was aware of the discovery by Krohn, I had worked out the details of the 

 hepatic organ in the genera mentioned in the text ; it was therefore highly 

 satisfactory to find his descrfption of this organ in A. mamillata agree so 

 closely with iny observations, particularly in A. mentula. 



