108 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



successive sections become more and more oblique as we pass from D to 

 P. The gradual increase in the length of the intervals between the 

 sections is another effect of the curvature of the stolon. 



The section which is figured slants upwards distally, so that the 

 animals, 21 and 20, nearest the proximal end, P, of the stolon are cut 

 through their nuclei and eleoblasts ; those which are a little more distal, 

 15 and 16, through their branchial sacs, gills and cloacae ; those a little 

 higher up, 10 and 11, through their ganglia, n ; 7 is cut through its line 

 of union with the ectoderm of the axial tube ; 6, through its area of com- 

 munication with the lower blood space ; 5, through its area of communi- 

 cation with the endodermal tube ; 4 and 3, through their communication 

 with the upper blood space ; 2, through the area of union with the ecto- 

 derm of the axial tube, and 1, above this, at the oral end of the body. 

 Between 1 and 7 the salpse are so crowded that there is no room for 

 the reference letters, and I therefore give on Plate XXXVII and Plate 

 XLVI more enlarged figures of these salpae, lettered and numbered 

 uniformly with the figures of Salpa cylindrica and Salpa pinnata. 



The section numbered 21 passes through the eleoblast, el, the 

 stomach, s, and the intestine, i : the middle plane of its body is at right 

 angles to the long axis of the stolon ; the dorsal surface external, and the 

 left side proximal. It is therefore a right-hand salpa, as are all the odd 

 numbers in the series. In the next four sections, 20, 19, 18 and 17, the 

 oesophagus is shown opening at m, into the right half, rb, of the pharynx, 

 which is separated from the left half, Ib, by the base of the gill, g. In 

 these four sections the heart, h, is also shown on the right side of the 

 body. The intestine, *', 20 and 21, opens through the anus, a, 17 and 18, 

 into the cloaca, 18, i, on the left side of the gill. The egg, o, is shown in 

 17 and 20. Figs. 15 and 16 still have their dorsal surfaces outwards, and 

 the middle plane at right angles to the long axis of the stolon, but the 

 endostyle is oblique, its right half in Fig. 16, and its left half in Fig. 15, 

 inclining towards the far side. This is the first indication we meet of 

 the primitive position of the salpae on the stolon, as we pass from the 

 aboral towards the oral end of the body, and careful examination will 

 show that it is the left half of the odd numbers or right-hand salpse, and 

 the right halves of the endostyles of the even numbers or left-hand salpae 

 which push in towards the opposite side. If the series from 14 to 6 be 

 carefully studied, it will be seen that the left halves of all the endostyles 

 finally lie to the left of the middle line, and the right halves of all of 

 them to its right. The series also show that all the hearts, in both right- 



