ON THE DIPLOOHORDA. 721 



not of a definite cellular structure. Thei-e is usually a paired 

 patch of this glomerular tissue on the antero- lateral surfaces 

 of the pericardial sac (figs. 1 and 5) in close proximity to the 

 internal apertures of the pre-oral canals. Further, the wall 

 of the ventral sinus shows a similar structure (figs. 3, 4, 

 and 7). In many cases the glomerular tissue of the ventral 

 sinus is also paired, and the ventral sinus is then almost 

 constricted into two paired sinuses. 



There is little doubt that this glomerular tissue is homolo- 

 gous with the pericardial gland or glomerulus of Balano- 

 glossus. Antero-dorsally to the pericardial sac we may 

 notice a pre-oral sinus bringing blood back from the buccal 

 shield (fig. 2) to the glomerulus. 



We may now briefly run over the figures given here, noting 

 the special points of each. Figs. 1 to 5 are selected from a 

 series of very nearly sagittal orientation. In fig. 1 the sub- 

 neural gland is cut almost throughout its length, its opening 

 into the pharynx being more to the right. The right collar 

 cavity is cut just at the apex of the gland, so that the sinus 

 is rather more to the right anteriorly than posteriorly. The 

 right glomerulus is also seen, whilst the cavity of the heart is 

 spacious, although not at its largest (in the median line). 

 The dorsal sinus is cut throughout its length, and two oral 

 grooves may be recognised. In fig. 2 the collar mesentery is 

 cut for some portion of its extent, and the glomerulus of the 

 ventral sinus is coming into view ; the left dorsal groove is 

 also just appearing. In fig. 3 the pericardial sac is cut in 

 the median line ; the peculiar shape of the heart is noticeable. 

 Further back the left collar cavity is alone seen, the dorsal 

 sinus is restricted, and the subneural gland is interrupted. 

 The left peripharyngeal and dorsal grooves are differentiated. 

 In fig. 4 the heart is no longer visible, but the left canal from 

 dorsal sinus into heart is seen. The posterior portion is still 

 more to the left, showing the grooves as before. Fig. 5 is 

 eight sections further to the left. In following the sinus one 

 notices the left pre-oral canal becoming gradually more pro- 

 minent, first laterally and then dorsally; the left glomerulus 



