352 A. T. MASTERMAN. 



out its relationships in the adult with some detail. Figs. 1 to 12 

 are drawings, by camera, of sections selected from a consecutive 

 series, cut nearly transversely to the long axis of the epistome. 

 In the sections in front of fig. 1 the whole interior of the 

 epistome is lined by the coelomic epithelium of the pre-oral 

 body-cavity {b. c. 1). At fig. 1 are cut the tips of the two 

 collar cavities, and in the centre the front end of the subneural 

 sinus. In fig. 2 there is further seen a space in the centre of 

 the subneural sinus, which is continuous with the pre-oral body- 

 cavity (see PI. 24, fig. 14), and the walls of which are thickened 

 and contractile. In life this space, in all likelihood, only 

 exists when its walls are in a state of contraction. In fig. 3 

 the tip of the subneural gland is seen, and in fig. 5 this organ 

 is to be noticed embedded in the sinus. The condition seen in 

 figs. 6, 7, and 8 may be found in a number of sections, and 

 probably represents the state of affairs when the walls are 

 collapsed. They all indicate the dorsal blood-vessel, with the 

 subneural gland lying in its lumen, though mostly resting 

 against the ventral coelomic wall. In fig. 9 (he tip of the gut- 

 wall is recognisable, and in PI. 24, fig. 10, the subneural gland 

 is observed to pass into it. Figs. 11 and 12 illustrate further 

 stages, which are readily understood with the help of fig. 13. 

 I would regard this dorsal diverticulum of the gut which 

 underlies the collar nerve-mass, and into which the subneural 

 gland is continued, as the enlarged base of the gland, and it is 

 at least possible that the stomodeeum extends as far as the 

 dotted line in fig. 13. 



The relationships of this subneural gland and its structure 

 are so closely identical with those of the similarly named 

 organ in Actinotrocha that a want of definite proof of an 

 epiblastic origin can hardly militate against the homology of 

 the two organs. If further evidence were required, the dis- 

 covery of other organs which have good claims to be regarded 

 as of notochordal value can be added. ^ 



What little light is thrown upon the question by study of 



* The above description has been checked by sagittal and coronal sections, 

 which, however, it would be superfluous to reproduce. 



