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JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



aboral region of the pharynx, 27-28, and the two gill-slits through 

 which the pharynx and the cloaca communicate with each other on 

 the sides of the gill. In cut R the outlines of the gill-slits are repre- 

 sented by dotted lines, while the outline of the cloaca is indicated by 

 a dark line. The rod-like gill, o, is also shown in this figure on the 

 middle line between the cloaca above and the pharynx below. Sec- 

 tion V passes through the same structures, and also through the 



CUT T. 



CUT U. 



CUT V. 



cloacal aperture, g'". It will be seen from these diagrams that the ven- 

 tral surface of each salpa joins the dorsal surface of the one next it on 

 the distal side, and that its dorsal surface joins it to the ventral surface 

 of the one next it on the proximal side or towards the root of the stolon. 

 The digestive tracts are so joined together that there is a continuous 

 endodermal tube, d', running in an uninterrupted course from the tip of 

 the stolon to the base, where, as is shown in Plate XXI, Fig. 1, d', and 

 also in Plate XIX, Fig. 4, d', and in Plate XXXV, d', this tube joins the 

 pharynx of the solitary salpa on its ventral surface, between the folds of 

 its endostyle, Plates XIX, XX and XXI, d-d. The diagrams also show 

 that the pharynx of each salpa is joined on its middle ventral line, 

 between the folds of its endostyle, to the dorsal surface of the next 

 beyond it, so that in this respect the anatomical relation which each 

 one bears to the one next beyond it is precisely the same as that in 

 which the solitary salpa stands to the first one in the series of chain- 

 salpae. 



I have represented each salpa in cut M as if it were joined to the 

 next by an unspecialized connecting tube, but there is no such tube 

 between the actual salpa3, which are separated in the diagram for the 

 sake of clearness. As section U shows, both ectoderm, a, and endoderm, 

 6, pass over from one salpa to the next directly, without the intervention 

 of any connecting tube, and this is shown still more clearly in Plate XV. 



