320 ME. A. HANCOCK ON THE ANATOMY 



not discover how the eggs passed from the ovary to the neigh- 

 bourhood of the branchial sac, and suggests the possibility of the 

 vas deferens acting also in the capacity of an oviduct. This, how- 

 ever, is exceedingly improbable ; and, from what I have seen, there 

 can be little doubt of the presence of a true oviduct, although I 

 do not consider my observation a sufficient demonstration of the 

 fact. But there can be no mistake as to the existence of a vas 

 defereois ; this tube is sufficiently conspicuous ; passing up by the 

 side of the alimentary canal, it penetrates the lower wall of the 

 cloaca, and terminates by the side of the anal outlet. The testis 

 is a much-branched organ ; the branches are extremely fine, and, 

 dividing dichotomously, terminate in numerous elongated fusi- 

 form vesicles, which are united in pairs ; or, in other words, the 

 ultimate twigs may be said to bifurcate, each branch being im- 

 mediately enlarged, so as to form an elongated cseeal vesicle. 



The blood-system in the Tunicata is perhaps the most difficult 

 branch in the anatomy to investigate ; for these animals are gene- 

 rally too minute and delicate to be successfully injected, and it is 

 not easy to obtain living specimens sufficiently transparent to 

 permit of the blood-current being traced through the tissues. 

 Nevertheless much good service has been done in this way by 

 M. Milne-Edwards and others ; but perhaps no one has done 

 more by this method than Dr. Lister, who had the good fortune to 

 meet with a species in every respect suited to the purpose. So 

 far as I have been able to ascertain, the blood-system has been 

 as fully, if not more fully, determined in Peropliora than in any 

 other Tunicate. It is therefore satisfactory to find that my 

 results perfectly agree with those obtained by Dr. Lister, so far 

 as they go *. This is particularly gratifying, as the mode of inves- 

 tigation adopted by me is very different from that followed by 

 this distinguished anatomist ; and, moreover, Peropliora is one of 

 the Social, while the species used by me are'all Simple Ascidians. 



I have relied almost entirely on dissection, aided by the accu- 

 mulation of blood-corpuscles in the various parts of the system. 

 In this way the minutest ramifications can be traced with the 

 greatest precision. A vast number of specimens, however, are 

 required ; for many individuals may be cut up before one is met 

 with in a proper state. Large specimens, too, are necessary ; and 

 they must have the tissues sufficiently transparent, and the blood- 

 globules opake or coloured ; in such only can the blood-channels 

 be distinctly traced. And when the specimens are even in the 

 * Philosophical Transactions, 1834, p. 375. 



