114 JOHNS HOPKINS UNIVERSITY MOEPHOLOGICAL MONOGRAPHS. 



A series of sections of this species, parallel to the long axis of the 

 stolon, and transverse to the bodies of the salpae, is shown in Plates XV, 

 XXIII-XXXIII and XXXVI, XXXVII and XXXVIII. 



Another stolon was cut into a series of sections at right angles to 

 those in these plates, but, in order to diminish the number of figures, I 

 have, instead of drawing all these sections, combined them to form the 

 solid pictures shown in Plates V, VI, VII, and Fig. 1 of Plate VIII. 



In these figures the numbered cross-lines indicate sections which 

 correspond, or nearly correspond, to the part of the figure which is crossed 

 by the line, but it is very difficult to secure exact correspondence in all 

 cases. 



As far as possible, I have shown corresponding stages in the two sets 

 of plates, but the salpa3 change so rapidly during their development that 

 the successive stages which are exhibited by one stolon may correspond 

 to the unrepresented intervals between the successive salpae in another 

 stolon, and I have not been so fortunate as to find two well preserved and 

 perfect stolons which are exactly alike. 



The departures from exact agreement are not very great, nor are 

 they of such a character as to perplex the reader, as they relate to slight 

 differences in the shape of the bodies or to slight variations in the relative 

 positions of the organs. 



Thus, for example, the line 41 in Plate VIII, Fig. 1, is represented as 

 passing through the process which unites each salpa in one series with the 

 ones diagonally opposite it in the other series. In Plate XXXVIII, how- 

 ever, section 41 actually passes through the bottom of the lower blood 

 space, i, and the connection between the salpa3 is cut in sections 50 and 61. 



This difference is partially due, perhaps, to distortion caused by 

 hardening and imbedding, but it is chiefly due to the fact that the two 

 specimens are not at exactly the same stage of development, although 

 they are so nearly alike that they can be compared without difficulty. 



I shall now describe the two sets of figures in detail. Plate V, Fig. 1, 

 shows a single salpa in the symmetrical position before the secondary 

 changes of position begin. The shaded area shows the extent of the fold 

 of ectoderm which separates this salpa from those adjacent to it, and it 

 will be seen that this fold is most developed where the stolon contains 

 internal organs, and least developed where it is empty. 



Thus the testicular folds of the genital string, Plate XV, Fig. 1, m, 

 and the lower portion of the egg, n, are shut into an ectodermal pocket, 

 while a little higher up, Figs. 2 and 3, the ectodermal folds are little more 



