124 A. H. L. NEWSTEAD. 



the adult. The epicardiac tubes become connected with the 

 process of budding. 



Van Beneden and Julin suggest that tlie perivisceral cavity 

 of Ciona represents the epicardiac tubes of Clavellina, which 

 have become enlarged, growing completely round the viscera 

 and fused together. 



The fact shown above that the perivisceral cavity communi- 

 cates with the posterior end of the pharynx by a pair of open- 

 ings affords a strong support to this view, which, however, can 

 only be completely accepted if it be confirmed by a study of 

 the embryological development of Ciona. 



The first stage of development which I have been able to 

 obtain is that of a larva which has recently become fixed. Figs. 

 3 — 5 are transverse sections of a larva at this stage. Fig. 3 is 

 the most anterior, and passes through the lower end of the 

 pharynx {ph.) below the opening of the oesophagus ; below the 

 pharynx are seen the stomach (5^.) on one side, and the intes- 

 testine (i.) on the other, the whole being surrounded by the 

 general blastocoele space (6.), containing numerous scattered 

 cells. 



A section a little further back (fig. 4) shows the endostyle 

 {end.) completely separated from the more dorsal portion of 

 the pharynx, which is now divided completely into two parts 

 {ep.) by a septum ; in a section still further back (fig. 5) we 

 find these two portions fused together, and much less in size. 

 From their mode of origin from the posterior end of the pharynx, 

 their fusion at their posterior ends, and their similar relations, 

 these two parts are evidently homologous with the epicardiac 

 tubes of Clavellina, so that the early stages of development of 

 Ciona are very similar to those observed in Clavellina. 



The first formation of the pericardium from these epicardiac 

 tubes I have not been able to follow ; the next stage of which 

 I have been able to get satisfactory preparations is one much 

 later, when the pericardium is fully formed and separated from 

 tbe epicardiac tubes which have grown round the viscera, and 

 become completely fused dorsally, though still separated ven- 

 trally by the pericardium. This stage is one during the 



