STUDIES ON THE PROTOCHORDATA. 315 



branchial sac] s'est developpe en un petit amas de cellules ; 

 c'est la I'ebauclie de la glande hypophysaire.^' 



A communication between the cavity of the central nervous 

 system and that of the branchial sac in the Tunicata has been 

 observed in several other cases by previous authors — thus by 

 Ganin (2) in the case of Didemnum (Diplosoma) gelatino- 

 sum, Keferstein and Ehlers (see Uljanin, 20) in the case of 

 Doliolum, Kowalevsky (7) for Pyrosoraa, Salensky (14 and 

 15) and more recently Metcalf (12 and 13) for Salpa^ Lahille 

 (11) and Hjort (5) for Distaplia magnilarva, and Hjort 

 again for Botryllus. 



From the observations of these authors, together with those 

 which I have recorded above, we may conclude that in all the 

 Ascidians the lumen of the hypophysis is in all cases at first in 

 direct communication with the lumen of the central nervous 

 system. And this forms the great difference, but at the same 

 time a very suggestive and instructive difference, between the 

 development of the hypophysis in the Ascidians and in the 

 higher Vertebrates. In the latter the lumen of the oral por- 

 tion of the hypophysis does not come into communication with 

 the cavity of the infundibulum, and this permanent separation 

 of the two parts of the hypophysis cerebri in the higher Verte- 

 brates may be compared with the temporary obliteration of the 

 lumen between the proximal and distal portions of the hypo- 

 physis which I have described above for Ciona. 



Julin's (6) and Balfour's (^Comp. Embryol.,' vol. ii, 

 p. 437) suggestion of the homology of the subneural gland 

 and dorsal tubercle taken together of the Ascidians, with the 

 pituitary body of the higher Vertebrates, founded on anato- 

 mical considerations, and especially worked out in great detail 

 by Julin, may be considered as being borne out fully by the 

 facts of development as described above. In the Ascidians, as 

 in the higher Vertebrates, the hypophysis cerebri consists of a 

 neural portion and an oral or stomodseal portion. The neural 

 portion of the hypophysis in the higher Vertebrates is the in- 

 fundibulum or processus infundibuli, and in the Ascidians it 

 may be that this is represented by the subneural gland. The 



