Pizon (22), in his v/ork on Botry llus , states that 

 he has made observatio s on the develop'nent of the dorsal 

 tube in the buds of a number of other Ascidians. In Perq- 

 phor aand Clave lina he observed tne tube over the dorsal v^all 

 of the branchial sac, but did not obtain stages which were 

 young enough to enable him to determine its origin. He con- 

 cludes, however, on the insufficient evidence of Kovmlev;sky 's 

 observations on Per ophora, that the dorsal tube arises as a 

 diverticuluiTi of the endoderrnal wall. Since in Glavelina the 

 later stages in the development of the dorsal tube are simi- . 

 lar to those of Perophora, he holds that in this Ascidian al- 

 so the origin is the sane. In two of tne Polyclinidae, viz: 

 Amaroucium proliferurn and Circinalium, in in Didemnurn niveun; 

 and in Astellium sponglf orrne, he has observed the dorsal tube 

 arising as an endodermal diverticulaTi, v/hich acquires a sec- 

 ondary opening into the branchial sac at its anterior extrem- 

 ity, just as in Botryllus . 



In none of tnese forms did he determine the origin 

 of the ganglion, but he comes to the unwarranted conclusion 

 that this structure is derived, independently of the dorsal 

 tube, in the sane way as he has described for the Bot rylli- 

 dae . 



Hjort (9) has recently studied the development of 

 the neuro-hypophyseal system in the buds of glossophormi sa- 

 bul osum, one of the Pol yclinidae , and Caullery ( 1) in Glos - 

 sop horum l\iteurn, Gircinali;m concrescens and Diplosoma gela- 

 tinosum, and although both of these authors find that the 



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