126 A. H. L. NEWSTEAD. 



although it has become twisted, still remains attached to the 

 wall of the pericardium along one edge, so that a study of the 

 development of the perivisceral cavity shows it to be very 

 different from the original blastocoele, and corroborates the 

 hypothesis put forward by van Beneden and Julin that it is 

 homologous with the epicardium of Clavellina. 



One small point may here be noticed, which, though of 

 little value by itself, yet when taken in conjunction with the 

 other evidence affords another point of similarity between the 

 perivisceral cavity of Ciona and the epicardiac tubes of Clavel- 

 lina. In Clavellina van Beneden and Julin state that the left 

 epicardiac tube is always larger than the right, and the same 

 fact may be noticed in the openings from the perivisceral cavity 

 into the pharynx in Ciona, the left opening in this case being 

 similarly larger than the right. 



D. Conclusions. 

 Two morphological conclusions may be drawn from the 

 above facts. 



(1) The primary condition of the epicardium is undoubtedly 

 that found in Clavellina, where it has the function of a budding 

 organ. The condition in Ciona is that of an organ which has 

 become very much modified while losing its original function 

 as an organ of budding. Since prolongations of the epicar- 

 dium or perivisceral cavity extend into the stolons of Ciona, 

 this supports the view which is adopted by Herdman (3, 4, 

 p. 139), that the stolons of Ciona are modified budding organs 

 which have lost their original function; the opposite view, 

 that the stolons of Ciona may be regarded as nascent organs, 

 which have not yet acquired their function of budding, is nega- 

 tived by the above facts, since the perivisceral cavity of Ciona, 

 if it be a modified epicardium as shown above, cannot be 

 regarded as a primitive condition. 



(2) This leads us to the second conclusion to be drawn from 

 the above facts. Roule (1) looks upon the perivisceral cavity 

 of Ciona as a primitive condition, corresponding to the general 

 blastocoele space which we find in the larvae, as well as in 



