2Q; Dr. Asajiro Oka : 



The nuclei of the cells are found mostly in the peripheral parts, 

 the centre being mainly composed of fibrous substance (PL II. , fig. 

 10). The longer diameter, which is placed antero-posteriorly, 

 measures almost 0, 1 mm. 



Neural gland. The neural gland lies immediately beneath the 

 nerve ganglion and is nearly of the same size as that organ. It is 

 bladder-like in structure with uniformly thick wall and a large 

 cavity in the interior. The wall is composed throughout of a 

 single layer of cells, the cytoplasm of which, however, seems not 

 to be clearly bounded, forming rather a sort of syncytium. The 

 dorsal portion of the wall is in close contact with the nerve gan- 

 glion, but the boundary between them is everywhere quite distinct, 

 and there is no area in which the tissues of the two organs 

 gradually pass over to each other^ (PI. IL, fig. 10). 



The central cavity of the neural gland communicates with 

 the exterior by means of a short duct which opens on the anterior 

 surface of the dorsal tubercle. This duct is of the same 

 width throughout except the terminal portion which is somewhat 

 widened so as to form a sort of funnel. At the very margin of the 

 opening, however, the duct is again a little constricted (PL IL, fig. 

 10). The wall of the duct is made up of cubical cells all over. 

 In the terminal portion of the duct, where it is widened, the cells 

 are provided with long vibratile cilia. 



A cross section though the middle part of the dorsal tubercle 

 is shown in PL IL , fig. 11. At the centre of the figure the ciliated 

 terminal portion of the duct of the neural gland is seen cut across. 

 On both sides the wall of the dorsal tubercle is formed for the 

 greater part by an epithelium of ciliated columnar cells, which is 

 the direct continuation of the epithelial layer of the peripharyngeal 

 ridge mentioned above. The peripharyngeal membrane is also 

 seen immediately on the dorsal side of this epithelium. The 

 posterior wall of the dorsal tubercle is formed of a thin epithelium 



1 According to M. M. Metcalf ('00), who made a special study of the intersiphonal organs 

 of various groups of Tunicata, there is in all the compound asoidians a region where the cells of 

 the ganglion and the neural gland merge into one another and are indistjnguishaole. 



