W. K. BROOKS ON THE GENUS SALPA. 117 



also at C in the figures in Plate XXVII. In Plate XXVII, C, the peri- 

 cardium, e, is shown in Figs. 1 and 2, and also the diverticulum, g, which 

 is to give rise to the digestive tract. Through an oversight, this is colored 

 green in the figures instead of red. It will be seen from Figs. 3 and 4 of 

 Plate V that the left pharyngeal pouch of a salpa which goes to the 

 right, Fig. 3, like the right one in a salpa which moves to the left, moves 

 much further from its primary position than the other pouch, and 

 becomes correspondingly reduced in cross section, as is shown by the 

 sections which we have just examined of the right pharyngeal pouch of 

 a left-hand salpa. The very small tubular upper part of this pouch, 

 shown in section in Plate XXX, Figs. 1 and 2, E, is the same as the 

 connecting tube, which is shown, at a very much older stage, in Salpa 

 cylindrica, at 27, in Plate VIII, Fig. 2. In Salpa pinnata, as in Salpa 

 cylindrica, it connects the dilated aboral end of the right-hand pouch of 

 the left-hand salpa, Plate V, Fig. 4 (or the left-hand pouch of the right- 

 hand salpa, Plate VIII, Fig. 2), with the corresponding side of the 

 endodermal tube, but in Salpa pinnata it soon degenerates and disap- 

 pears, as will be shown soon, while it is present in advanced embryos of 

 Salpa cylindrica. 



We have now to examine the sections through the left half of the 

 left-hand salpa, shown in Plate V, Fig. 4. Plate XXX, Fig. 3, E' shows 

 the union of the oral ends of the two pharyngeal pouches. 



Figs. 2 and 1, E', show the communication between the left one, 28, 

 and the endodermal tube, d', and they also show the ganglion s, proximal 

 or dorsal to the endodermal pouch and at the level of the connecting 

 tube. In Plate XXIX, Fig. 2, c', the section cuts the left perithoracic 

 vesicle, h, and the left pharyngeal pouch, 28, just below the endodermal 

 tube. C' in Fig. 1 shows the communication between these two organs, 

 as does also c' in Plate XXVIII, Figs. 1 and 2; d, in Fig. 3 of Plate 

 XXVII, cuts the aboral ends of the pouch and vesicle, and d in Figs. 2 

 and 1 passes below these structures. 



It will be seen by comparing Plate V, Fig. 3, with Fig. 4, and by the 

 examination of the sections, that the pericardium, e, is always in relation 

 to the aboral end of the right pharyngeal pouch, and that the digestive 

 organs always arise from this pouch, whether it is the larger, as it is in 

 a right-hand salpa, Fig. 3, or the smaller, as it is in a left-hand salpa, 

 Fig. 4. 



The next figure, Plate VI, Fig. 1, is a dorsal or proximal view of a 

 right-hand salpa at the stage which is shown at H-H' in the sections on 



