W. K. BROOKS ON THE GENUS SALPA. 79 



as Plate XXXIV, Fig. 10 and Plate XXIII, Fig. 7 show. As the result of 

 this process the nerve tube becomes cut up into a series of ganglia, one 

 for each salpa, Plate XV, Fig. 10, s ; the perithoracic tubes become cut 

 up into a series of perithoracic vesicles, two for each salpa, Plate XXXIV, 

 Figs. 9, 10 and 11, and Plate XV, Figs. 11 and 12, g and h ; the genital 

 string becomes cut up into a series of eggs, Plate XV, Fig. 2, n, one for 

 each salpa, inclosed in a follicle, m; and the thickened endodermal 

 epithelium at the sides of the endodermal tube, d', becomes cut up into a 

 series of vertical pouches or pockets, two for each salpa, the rudiments of 

 the right half of the pharynx, 27, and of its left half, 28, as is shown in 

 Plate XXIII, Figs. 4, 7, 8 and 9, and Plate XV, Figs. 6, 7, 8, 11 and 12, 

 where these pouches are colored red. 



III. The Rudimentary Chain-Salpa. The structures which I have 

 enumerated form the rudiments of a single salpa. They are shown in 

 Plate V, Fig. 1, which is a reconstruction from a series of tran verse sec- 

 tions through the stolon of Salpa pinnata. 



At this stage each salpa is bilaterally symmetrical, and its plane of 

 symmetry is the same as that of the stolon, while its long axis is at right 

 angles to that of the stolon, which becomes converted into a single row 

 of salpae, so placed that, as is shown in cut M, the dorsal surfaces of all of 



CUT M. 



them are towards the base of the stolon, their ventral surfaces towards 

 its tip, their right and left sides on its right and left respectively, their 

 oral ends at its top or neural side, and their aboral ends at its bottom 

 or genital side. 



IV. The Secondary Changes. The single row of salpae becomes con- 

 verted into a double row, Plate IV, Fig. 1, which consists of a series of 

 right-handed salpae and a series of left-handed ones, placed with their 

 dorsal surfaces out, their ventral surfaces towards the ventral surfaces 

 of those in the opposite row, and the left sides of those on the right and 

 the right sides of those on the left towards the base of the stolon. In 



