EXPLANATION OF PLATES. 381 



The red marks the endodermal tube of the stolon and the endoderm of the chain- 

 salpa ; the yellow, the blood tubes of the stolon and the body cavities of the chain- 

 salpa ; the blue, the follicle and its derivatives ; the purple, the ectoderm and gang- 

 lion ; the orange, the eggs, and the green, the perithoracic tubes. 



At this stage the bodies of the chain-salpse lie in their primary positions, and the 

 middle plane of the stolon is also the middle line of each salpa, as is shown by Plate 

 V, Fig. 1. At the top, Fig. 10, and bottom, Fig. 1, of the stolon, the body cavities of 

 the salpse are completely shut in by the ectoderm, but in all the other sections they 

 communicate with the blood tubes of the stolon. 



Figure 1, a section close to the ventral surface of the stolon showing the testi- 

 cular folds m, m of the follicle. 



Figure 2, a section a little higher up, showing the series of eggs, n, partially 

 separated from each other by infoldings of the follicle. 



Figures 3 and 4, sections through the ventral blood tube. 



Figure 5 cuts the left perithoracic tube (green) and the left half of the pharynx 

 (red). 



Figure 6 : the left half of the pharynx, 28, is cut in the plane of its communication 

 with the endodermal tube, d', of the stolon, while the right half of the section lies 

 below the endodermal tube and cuts the ventral blood tube, i. 



Figure 7 : a section in the plane of the endodermal tube, d', of the stolon, showing 

 its communication with both the left half of the pharynx, 28, and the right half, 27. 

 The section passes through the right perithoracic tube, g, and the heart, e, but it 

 passes above the left perithoracic tube. 



Figure 8 : the right side is nearly the same as in Fig. 7, but on the left the sec- 

 tion cuts the dorsal blood tube,/, and the dorsal elongation of the left half of the 

 pharynx, 28. 



Figure 9 : the right half of the section cuts the tips of the dorsal elongations of 

 the right tubes of the pharynx. 



Figure 10 : a section through the ganglion, s, close to the top of the stolon. 



Figures 11 and 12, parts of sections 5 and 6, more enlarged. 



Figure 1 is the first section in the series ; Fig. 2, the sixth ; Fig. 3, the eighth : 

 Fig. 4, the fourteenth ; Fig. 5 is not in the same series ; Fig. 6 is the twentieth ; Fig. 

 7 is the twenty-fifth ; Fig. 8, the twenty-ninth ; Fig. 9, the forty -fourth, and Fig. 10, 

 the fifty-fifth. All the figures except Fig. 5 and Figs. 11 and 12 are drawn with the 

 top distal or towards the tip of the stolon, and with its right side on the right of the 

 figure. 



PLATE XVI. 



Figures 1, 2 and 3 are in the same series with Figs. 1, 2, 3, and 4 of Plate XVII. 

 They are horizontal sections of an embryo of Salpa pinnata, a little older than the one 

 shown in Plate XXII. 



Figure 1 is the thirty-sixth section in the series ; Fig. 2, the forty-fourth ; Fig. 3, 

 the fifty-third ; Fig. 4 of Plate XVII, the sixtieth ; Fig. 2 of Plate XVII, the sixty- 

 sixth ; Fig. 3, the seventy-fourth and Fig. 4, the sixty-first. 



Figure 4 of Plate XVI is a transverse section through the stolon and endostyle 

 of an embryo, at the stage which is shown in Plate XLI, Figs. 5 and 6. 



Figure 5 is a longitudinal section of a stolon from an embryo at the stage shown 

 in Plate XLI, Figs. 3 and 4. 



Figures 6 and 7 are two stages in the history of the ectoderm ; Fig. 7, from the 

 embryo, shown in Fig. 2 of this plate, and Fig. 6, from a younger embryo. 



