branchial sacs, and gradually extending dorsally, fuse to- 

 gether on the median line. These sacs are not formed at the 

 same time, but one is given off from the inner vesicle before 

 the other, so that at a very early stage an asymmetry of the 

 bud is produced. 



Delia Valle (4) described a sim.ilar method of form- 

 ation of the peribranchial cavity for Botryllus , but both 

 Pizon (22) and Hjort (8) have conclusively proven his obser- 

 vations to be erroneous. 



According to these authors both the lateral and me- 

 dian portions of the peribranchial cavity arise at the same 

 time as a saddle-shaped bag, which is cut off by two longi- 

 tudinal furrov/s from a median vesicle, the later branchial 

 sac. Hjort regards this process as a great curtailing of 

 the embryonic development, such as often takes place in buds. 



Salensky (27) confirms this conclusion, but goes a step 

 further, saying that, "die Entwicklung der Peribranchialhohl- 

 en des Botryllus eine Abkurzung nicht nur beziiglich der era- 

 bryonalen Entwicklung, sondern auch beziiglich der Entwicklung 

 dieser Organe in den Knospen anderer Ascidien darstellt." 



My observations on the development of this struc- 

 ture in Perophora viridis, although agreeing with those of 

 Iijort, in so far as they show that the peribranchial sacs do 



not arise separately as closed vesicles, which later unite to 



the 

 form clcacal cavity, indicate that the process is not so sim- 

 ple as that which occurs in B otryllu s . 



If a transverse section of a bud be examined about 



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