Dr. Asajiro Oka: 27 



ascidian and not with the inner surface lining the central cavity of 

 Pyrosoma. In Cyathocormus the case is wholly different. The 

 central cavity of C yathocormus-eolouy exactly corresponds with 

 that of Pyrosoma both morphologically and functionally, the 

 cavity in question representing in both cases the common cloaca of 

 the whole colony. That a diaphragm is present in one form and 

 lacking in the other is not of much importance, since the mode of 

 life is entirely different in these aninials, and the diaphragm, 

 though highly useful in making the jet of water more powerful in 

 a swimming animal, would be of no use in a sedentarj^ colony. 



So far as I can judge, the form of colony of Cyathocormus might 

 most naturally be deduced from that of Diplosoma, such as is figured 

 in Bronn's Klassen und Ordnungen des Tierreichs, III. Suppl. p. 

 184, or in Lahille's work (' 90) p. 112. If we imagine the base 

 of attachment of such a colony to become smaller and the common 

 cloacal opening larger, until the shape of the colony has become 

 cylindrical, we would have practically the same form of colony as 

 it really occurs in Cyathocormus. In all probability, the thoracic 

 region, lying nearest the superficial layer of test, would have kept 

 its position perpendicular to the w^alls of the cylindrical head, while 

 the abdomen, being connected with the base of the colony by 

 means of the vascular appendage projecting from its posterior end, 

 would be bent downwards and cover the thorax of the zooid 

 lying next below on the inner side. In like manner, the test 

 substance enveloping the vascular appendages of various zooids 

 now arranged in longitudinal rows would fuse together to form 

 compact masses. In short, the colony would be converted to one 

 exactly similar to that of Cyathocormus. 



It is, however, equally possible that the colony of Cyatlwcormus 

 has been produced in the following way. Suppose a club-shaped 

 colony of compound ascidian, such as Colella murrayi or C. quoyi, 

 for example, has lost a part of the test substance at the top as w^ell 

 as in the interior of the head. The colony would in this case also 

 become cup-shaped and would very much resemble a Cyathocormus 

 colony. Moreover, the mode of formation of the colony might, 

 in all probability, be much the same. In Cyatlwcormus, as in the 



