246 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



Barrels says (4), p. 467, that he has not been able to decide whether 

 it is the thick border of the opening of the oviduct or a new formation. 



Plate XI, Fig. 3 shows the embryo in its follicle projecting into the 

 atrium c, and inclosed in the epithelial capsule 6', which is continuous at 

 the bottom of the figure with the epithelium of the walls of the atrium. 

 At a stage a little older, Plate XLI, Fig. 1, 23, it runs down for some 

 distance beyond the outline of the embryo, and forms the wall of the 

 placenta. The figures 24 and 31 are in the cavity of the placenta. At a 

 still lower level the capsule is constricted to form the narrow neck of the 

 placenta, through which its cavity communicates with the body cavity 

 of the chain-salpa. 



In Salpa hexagona, Plate XI, Figs. 4, 5, 6, 7, 8, &', that part of the 

 capsule which incloses the embryo is not in close contact with it, but 

 separated from it by a space which is well shown in the figures. 



In Salpa pinnata, on the other hand, Plates XII, XIII and XIV, 6', 

 it is so closely applied to the follicle cells of the embryo, at least in speci- 

 mens which have been hardened and imbedded for sections, that very 

 careful examination of the horizontal sections is needed to find it. 



SECTION 3. The Supporting Ring. 



As shown in Plate XLI, Fig. 1, the cells of that portion 23 of the 

 epithelial capsule which lies below the level of the embryo soon become 

 elongated, so that the wall here becomes much thickened to form that 

 portion of the placenta which I shall call the supporting ring; the 

 structure which is shown at 23 in the figures. It is well shown in the 

 embryo of Salpa hexagona at 23 in Plate XLI, Figs. 2, 3 and 4, and 

 in Salpa pinnata, in Plate XXII, Plate XVIII and Plate XXXV, as well 

 as in the woodcuts on pages 29, 30 and 31. 



At first the transition from the thinner portion 6' which covers the 

 embryo to the thickened portion which is to form the supporting ring 

 23, is gradual, as is shown in Plate XLI, Fig. 1, and in the diagram in 

 Plate XII, Fig. 11. The line between the two regions soon becomes 

 abrupt and strongly marked, cut B, and in Salpa pinnata, XXII, Fig. 1, 

 the upper edge of the supporting ring soon bends inwards towards the 

 axis of the placenta in such a way as to interrupt its continuity with the 

 portion around the embryo. 



In Salpa hexagona this continuity persists, Plate XLV, Fig. 4, 23 and 

 B', as long as the epithelial capsule is retained, and the history of the 



