116 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



ventral surface of the body, to form the oral end of the pharynx. This 

 communicates directly with the aboral end of the right pharyngeal 

 pouch, 27, as will be seen by examination of the series of sections of B in 

 Plates XXXI and XXX. At the stage which is shown in Plate V, Fig. 2, 

 the oral end of the pharynx communicates, through a long connecting 

 tube over the upper surface of the stolon, with the aboral end of the left 

 pharyngeal pouch, 28, but this connecting tube, which, as we have seen, 

 persists in Salpa africana and Salpa cylindrica, Plate VIII, Fig. 2, 28, 

 until the chain-salpa is perfectly developed, is very transitory in Salpa 

 pinnata, and in salpa B-B' in the sections it has begun to degenerate 

 and disappear. At the level of sections 3 and 2 of Plate XXXI it is 

 shown at B, but in section 1 of this plate there is no trace of it and the 

 body cavity of B' is empty. It reappears again at B in Plate XXX, 

 Fig. 3, and in Fig. 2 the opening of the left pharyngeal pouch, 28, into 

 the endodermal tube, d', is shown, and still lower down, at B' in Plate 



XXVIII, the communication between the left perithoracic vesicle, h, and 

 the left pharyngeal pouch, 28, is shown. 



Plate V, Fig. 3, is also a right-hand salpa, a little older than Fig. 2. 

 Both halves of the body have begun to move downwards, or towards the 

 genital side of the stolon, and the only trace of the connecting tube of 

 Fig. 2 is a short prolongation, 28', from the oral end of the pharynx. 

 This prolongation can be traced up towards the top of the stolon for a 

 short distance, but it soon disappears, so that the only communication 

 between the oral and the aboral ends of the left half of the pharynx, 28, 

 is now through the endodermal tube, d'. 



Plate V, Fig. 4, shows a left-hand salpa in which the connecting 

 tube has completely disappeared, and the halves of the body have moved 

 down so far that the ganglion, s, is on the level of the ectodermal tube, d, 

 as is also shown in the section of the salpa E-E' in Plate XXX, Fig. 2. 

 Above the endodermal tube the body cavity is now empty, as shown at 

 E-E' in Figs. 1, 2 and 3 of Plate XXXI, and there is no trace of the 

 connecting tube. The greater part of the right pharyngeal pouch, 27, 

 now lies below the level of the endodermal tube, d', and its aboral dilated 

 end is joined to the right side of the endodermal tube by a constricted 

 tubular prolongation, which is shown, in section at E, in Figs. 1, 2 and 3 

 of Plate XXX. Fig. 3 cuts it at E below the level of the endodermal 

 tube, while Figs. 1 and 2 show its opening into this tube. In Plate 



XXIX, Fig. 2, it is cut at C, as it begins to expand, and at C in Fig. 1 

 its communication with the right perithoracic vesicle, g, is shown, as it is 



