90 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



with all their dorsal or neural surfaces turned towards its base, and their 

 ventral surfaces towards its tip ; that this single row is converted into a 

 double row by the passage of all the odd salpae to one side and all the 

 even salpae to the other, and that each salpa rotates on its own axis 

 so that all their dorsal surfaces come to face outwards, and all their 

 ventral surfaces towards those of the opposite salpa3, sounds very simple. 



In reality the changes are far from simplicity, and they are extremely 

 difficult to study or to describe in detail. 



I have enumerated them in succession and they must be so described, 

 but they all go on simultaneously, and they begin at a very early stage, 

 so that all the space relations of the body of each salpa are changing 

 continually during its development ; nor do the changes affect all parts 

 of the body alike, the oral ends with the ganglia being the first to move 

 out into two ranks and the last to rotate. 



The oral ends of the bodies, and the ganglia, which are marked s in 

 the figures, move from their primitive position on the middle line of the 

 stolon at a very early stage, as is shown in Plate V, Fig. 2, although 

 in Salpa cylindrica, Plate VIII, Fig. 2, long after the aboral or nuclear 

 end of the body has assumed its secondary position, with the dorsal 

 surface and cloacal aperture, g v , turned outwards or away from the axis 

 of the chain, the ganglion s still lies on the proximal surface of each 

 salpa, that is, on the surface which is turned towards the base or prox- 

 imal end of the stolon, as is shown in the sections of the same stage in 

 Plate XL. In this plate, as in all the others which represent sections of 

 chain-salpae, the base or proximal end of the stolon is towards the bottom 

 of the page, and the right side of the stolon is on the right side of the 

 figure. 



The ganglion of a salpa which has moved to the right is shown at s 

 in Figs. 14, 15 and 16, and the ganglion of one which has moved to the 

 left at s, in Figs. 19 and 20, and it will be seen that even at this late stage 

 the ganglia on both sides of the series are proximal, although the aboral 

 ends of the bodies have rotated into their secondary position, as is shown 

 in Plate XXXIX, Figs. 10, 11 and 12. 



The fact that these changes take place gradually and simultaneously 

 and affect different parts of the body in different ways, renders a clear 

 conception of their character an indispensable preliminary to the study 

 of sections of the stolon, but, unfortunately, the converse is also true, and 

 a clear conception of the character of the secondary changes can only be 

 gained by the study of the details of the process of development. 



