28 MKITISH TUNICATA. 



\vas Ascidia mamillata ; and although he appears to have 

 traced with great accuracy the development of the organ, he 

 seems to have failed in detecting the duct in the adult animal. 

 From the general characters, however, obtained by his exami- 

 nation of the young and adult combined, he is disposed to 

 conclude that the " secretion prepared in the ca3ca must be 

 accessory to digestion ; but whether or not the watery secre- 

 tion is bile, and the gland therefore a liver," he concludes, 

 "must for the present be left undecided." Nevertheless, after 

 the above description of the numerous modifications of the 

 organ, and particularly when the position of the duct in re- 

 lation 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. 



The reproductive organs are well developed in the Tuni- 

 cates ; and in all of them the two sexes are combined in the 

 same individual, though the male and female elements are 

 always secreted by distinct organs, which,, however, 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 Cynfhiada? the testis has been 

 entirely overlooked .- the oviduct and ras deferens are likewise 

 constantly distinct. 



In Axi'-idia xordida 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 (PI. XIII). 

 The oviduct passes through the loop, and, following the 

 curvature of the intestine, opens by the side of the anus 

 into the cloaca. The vas deferen* terminates near to the 

 same point, and is adherent to the oviduct throughout its 

 course [as in A. mcntnla, see fig. 1"2, p. 62]. In the vicinity 

 of the ovary it receives several much attenuated branches 

 from either side of the intestine; these divide dichotomously, 

 the ultimate twigs terminating in elongated and irregularly- 

 lobulated vesicles which are spread over the intestinal tube, 

 and which also exhibit a tendency to dichotomous division: 

 these vesicles secrete the male element. 



In A. xcalira, A. affini*, A. mentula, and A. venoxa the same 

 arrangement of the reproductive organs is apparent ; but the 

 ovary in A. mentnla is a lobulated organ, and, lying within 

 the loop of the intestine, is seen at both sides of the ali- 

 mentary tube, and consequently has the appearance of being 



