W. K. BROOKS ON THE GENUS SALPA. 109 



hand and left-hand salpae, are adjacent to the right halves of the endo- 

 styles, and the study of younger specimens shows that all the hearts and 

 all the stomachs and intestines are derived from the right side of the 

 stolon. 



In 8, 9 and 10 the ganglion, n, is towards the base of the stolon, and 

 the right sides of all three salpae towards the right side of the stolon. 

 Although these three sections form a double row, as they do at a lower 

 level, the sections in this plane show that this is only apparent, and is 

 due to the necessity for room for the great ganglia of the closely packed 

 series of animals. The figures show that the series is, in reality, a single 

 row of animals with their neural surfaces towards the base of the stolon, 

 and with one-half of the pharynx with its half of the endostyle com- 

 pressed into the space between two other animals, while the other half is 

 free and enlarged. 



In 7, which is shown more magnified in Plate XLVI, Fig. 2, the left 

 half of the pharynx, Ib or 28, and the left half of the endostyle, d, 2, 

 are obviously on the right of the stolon, although the animal- itself is a 

 right-hand salpa. Its ectoderm is continuous with the ectoderm of the 

 bottom of the stolon. 



Section 6, shown also in Plate XLVI, Fig. 2, is a left-hand salpa at 

 the level at which its body cavity is continuous with the lower blood 

 space, all or i. The right half of its pharynx, 27, and the right half of 

 the endostyle, d, 1, are separated from the corresponding structures on 

 the left, 28 and d, 2, by the space i. 



Section 4, which is also shown more enlarged in Plate XXXVII, Fig. 

 25, is a left-hand salpa at the level of its communication with the endo- 

 dermal tube, d'. This tube is cut obliquely, so that the flat surfaces of 

 its upper and lower walls are shown as well as its cavity. This figure 

 shows that the endodermal tube is really part of the pharynx, and that 

 half of the endostyle, d, 1, lies on one side of it, and the other, d, 2, on 

 the other. 



In section 3, shown also in Plate XXXVII, Fig. 26, the body cavity 

 communicates with the upper blood space, j, which separates the right 

 half of the pharynx, 27, from the left, 28, and these two chambers have 

 here no connection with each other, although still higher up, at the level 

 of section 2 and section 1, they meet and unite to form the oral end of 

 the pharynx. 



If now we construct in imagination the body of a single salpa from 

 this series of sections, we shall find that the cavity of the stolon is really 



