100 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



p, and the latter now opens into the cloaca, at p". Plate VI, Fig. 2, is a 

 proximal or dorsal view of a right-hand Salpa pinnata at this stage, 

 showing also beyond it, and partially hidden by it, a left-hand salpa. 



In both figures, g is the left and h the right perithoracic vesicle, and 

 g'" the cloaca. Plate VI, Fig. 3, is the opposite or ventral view of the 

 same right-hand salpa, showing the gill-slits or the openings of the 

 perithoracic vesicles, g and h, into the pharyngeal pouches, 27 and 28, and 

 this figure also shows that the posterior branches of these pouches do not 

 yet communicate with each other, although the oral end of the pharynx 

 has been formed by the union of the oral ends of the two pouches, as 

 cuts P and Q show. Plate VII, Fig. 1, is a more highly magnified ven- 

 tral view of the aboral end of the right-hand salpa shown in Figs. 2 

 and 3. In this, as in the other figures, 27 is the right pharyngeal pouch, 

 and 28 the left, and g and h are the openings or gill-slits which lead from 

 them into the perithoracic pouches. Beyond or dorsal to the rudiment 

 of the testis, x, is the atrium or cloaca, which is represented as seen 

 through the transparent testis. The space in which the testis lies is to 

 become the cavity of the gill, and, as the figure shows, it is bounded 

 dorsally by the atrium, and at the sides by the pharyngeal pouches. It 

 is not yet closed or shut in ventrally, as it will be when the pharyngeal 

 pouches unite with each other. 



The cavity of the gill is also shown, in the same condition, in Plate 

 XXXIII, Fig. 3, K-K', where it is colored yellow. The letter m in this 

 figure lies in the gill, which will be seen to be bounded dorsally by the 

 cloaca, green, and at the sides by the red pharyngeal tubes 27 and 28, 

 while it is as yet open on its ventral side. A little farther back, Figs. 2 

 and 1, K-K', it is open both dorsally and ventrally. 



In the ventral view, Plate VII, Fig. 1, the pericardial vesicle, e, is 

 shown as a closed hollow vesicle lying against the ventral surface of 

 the posterior end of the right pharyngeal pouch, 27, and, dorsal to it, 

 the postero-median angle of the right pharyngeal pouch gives rise to the 

 oesophagus, q', which leads to the stomach, p', from which the intestine 

 runs towards the dorsal surface to the anal end p", where it joins the 

 cloaca. In the figure the dorsally placed intestine is represented as 

 seen through the ventral pericardium, e, and the wall of the right 

 pharyngeal pouch. The pericardium is also shown at e in the sections 

 of the salpa, K-K, in Plate XXXII, Figs. 6, 7 and 8, and in Fig. 7, K-K', 

 the oesophagus is shown, colored green, at g, and the cross section of the 

 intestine is also shown in this figure and Fig. 6, colored blue. 



