106 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



the adjacent salpae, and an axial portion in which the communication 

 between adjacent salpae persists until just before birth, when it degen- 

 erates and disappears. 



Transverse sections like those from which the figures in Plates VII 

 and VIII were constructed look as if the salpae had been formed on 

 opposite sides of a connecting tube, and in fact from a physiological 

 point of view this is, practically, the result of the process, for the tube 

 which is shown in these figures lies in the same place as the original 

 stolon, and serves the same purposes in nutrition, although it will be 

 seen that, morphologically, it is in no sense the same as the undiffer- 

 entiated stolon, but rather the middle regions of the bodies of the salpae, 

 retaining their original positions after their oral and aboral ends have 

 pushed out of the line. In any transverse section of this tube, at the 

 stages shown in Plates VII and VIII, it is part of the body of a salpa, 

 although it is a part which is destined to degenerate and disappear, just 

 before the birth of the salpa3, after it has served its nutritive purpose. 



Since the right and left pharyngeal pouches of each salpa retain for 

 some time the connection with the endodermal tube, d', which is shown 

 in diagrams W and X, it is plain that the anatomical relations of the 

 right half of the pharynx must be different from those of the left, and 

 that those of the left half of a right-hand salpa are like those of the right 

 half of a left-hand salpa. The right pharyngeal pouch, 27, of a right- 

 hand salpa undergoes little change as it pushes to the side, and its direct 

 connection with the right side of the endodermal tube persists, while the 

 oral and aboral ends of the left pharyngeal pouch, 28, of a right-hand 

 salpa are pulled out into long tubular channels of communication with 

 the left side of the endodermal tube. 



These peculiar relations are, of course, reversed in a left-hand salpa. 

 Here it is the left pharyngeal pouch, 28, which retains its immediate 

 connection with the endodermal tube, while the communication between 

 the two ends of the right one, 27, is through the long tubes. 



If now we imagine each salpa to complete its development in the 

 way we have already described, and then to rotate on its own axis, we 

 shall have a series of salpae like Plate VIII, Fig. 2, which shows in the 

 foreground the left side of a right-hand individual of Salpa cylindrica, 

 together with that part of the axial tube which pertains to its own body, 

 and in the background the right side of a left-hand salpa partially 

 hidden. 



