REPORT ON TFTE TUNICATA. •>."> 



Then again, in Ecteinascidia turbinated, where the eonnecting ducts ;ire not expanded 

 and triangular (PI. XXXVI. fig. 3), the languets arc merely finger-like processes 

 (PL XXXVI. fig. G, /.), and running down the two sides of the d irsal area are a series of 

 processes, which are shaped exactly like the connecting ducts, but are free at their ends, 

 like the languets beside them (PL XXXVI. fig. 6). Hence, it seems to mc that there 

 can be little doubt that the languets, and therefore the ribs and teeth of the dorsal lamina, 

 correspond to the connecting ducts of the branchial sac, and not to the papilla,' of the 

 internal longitudinal bars. 



In conclusion, I give a table (page 286), showing what seem to me to be the 

 genetic relationships between the different groups of the Ascidise Simplices. As this is 

 founded merely upon the anatomy of the adult forms, it is of course liable to contain 

 errors of detail, but the main lines are probably correct. The wisdom of attempting to 

 form a genealogical scheme out of such insufficient data, will, I doubt not, be cpuestioned 

 by some, but if of no further value, the table serves at least to show the connection in 

 some of the most important points of structure between the different genera. 



The ancestral form of all the Simple Ascidians I imagine to have been something like 

 a Clavelina without a peduncle (A. in the table). That is to say, it had a body which was 

 elongated antero-posteriorly, so as to allow the stomach to lie behind the branchial sac ; 

 it had unbranched tentacles, and a simple branchial sac, with no folds and no internal 

 longitudinal bars; and finally, it had the power of reproducing by gemmation. From such 

 a form it is easy to derive Clavelina, by the change (shown at 1) of the posterior end of 

 the body into a peduncle. Before this took place, however, two series of forms must ' 

 have split off from the main line: one of these, by a change (2) in the relations of the 

 branchial sac and the stomach, produced the genus Perophora, while the other, by 

 the development of internal longitudinal bars in the branchial sac, became a form (P>.) 

 which was probably the common ancestor of all the other Simple Ascidians, and which, by 

 the addition of a peduncle (3), attained the structure of Ecteinascidia. 



After this point a change must have taken place in the main line, from B. onwards, 

 resulting in the loss of the power of reproducing by gemmation, as this quality is 

 possessed by none of the remaining groups ; and thus a form was produced, having all 

 the characters of the genus Ciona. This was the common ancestor of the AscidiidaB, 

 the Cynthiidse, and the Molgulidae, and, after the separation of a form (C.) having the 

 branchial sac folded, of the AscidnVke alone. From this central Oiona-]ike being, 

 Abyssascidia and Corella on the one hand, and PachychUma and Ascidia on the other, 

 may be derived, by changing the relations of the stomach to the branchial sac in a manner 

 which has been already described (page 283). 



Eeturning to C, the common ancestor of the Cynthiidaa and MolgulidaB, we find it 



1 This and other objectionably dogmatic words which occur in the following description an- merely used to avoid 

 circumlocution. As has been already Btated, I fully recognise the hypothetical nature el' these investigations. 



