ON THE PERIVISCERAL CAVITY OF CIONA. 123 



as the orifices described by Kupffer, it is extremely probable 

 that the supposition of van Beneden and Julin is correct, and 

 that the orifices observed by Kupfi'er open into the peri- 

 visceral cavity, and not, as he described, into the atrial cavity. 

 Since no openings can be found in a whole series of sections 

 between the atrial cavity and the perivisceral cavity, and since 

 Roule expressly denies their possible existence, it appears cer- 

 tain that such communications between the two cavities do not 

 exist. 



c. Development in the Larva. 



The early stages of development of Ciona are passed through 

 very quickly; the tailed larvae are formed in the first twenty- 

 four hours of development, and fixation takes place on the 

 second day, the changes at this time being passed through 

 very rapidly, so that the development is very difficult to follow 

 through all its stages. 



I have unfortunately not been able to follow out completely 

 the development of the perivisceral cavity in the early stages, 

 but the comparison of the stages observed with the develop- 

 ment of the epicardium of Clavellina, as observed by van 

 Beneden and Julin (1), shows the process of development to be 

 very similar in the two forms, and supports the hypothesis put 

 forward by these authors that the perivisceral cavity of Ciona 

 is homologous with the epicardiac tubes of Clavellina. 



The process of development in Clavellina is shortly as fol- 

 lows: — Two tubes are first formed as outgrowths of the pharynx, 

 called by van Beneden and Julin the "epicardiac tubes;" 

 these later become fused with one another posteriorly, and the 

 posterior fused portion then becomes separated from the epi- 

 cardiac tubes to form the pericardium. The dorsal wall of the 

 pericardium invaginates to form the heart, so that the heart is 

 at first completely open along its whole length to the primi- 

 tive blastocoele of the larva; later the pericardium becomes 

 closed, while the heart remains attached to its dorsal wall by 

 a kind of mesentery, and open only at its ends to the general 

 blastocoelic space, which develops into the vascular system of 



