110 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



part of its body cavity, and that each salpa is joined on to adjacent 

 salpae in the way shown in cut M, which is a diagram constructed from 

 sections of Salpa af ricana. 



In Salpa cylindrica the secondary changes take place so slowly that 

 the young chain-salpa becomes fully developed, or nearly so at least, 

 before they are completed, and this species is therefore very well adapted 

 for use as an illustration, and as a key to the more obscure histories of 



i 



other species. 



I have therefore figured a series of transverse sections through the 

 bodies of two salpae of this species, a right-handed one and a left-handed 

 one, in Plates XXXIX and XL, at the most instructive stage. These 

 figures, like the others, are placed so that the side of the section which is 

 nearest the base of the stolon is at the bottom, and that which is to the 

 right of the axis of the stolon, on the right of the figure. The sections 

 are numbered in succession, so that Fig. 1 is at the aboral end, and Fig. 

 23 at the oral end of the series. 



I have also made from another stolon of the same species at the 

 same stage, another series of sections, at right angles to those in the 

 plates, or transverse to the axis of the stolon, and I have superimposed, 

 with a camera, the outlines of these sections in such a way as to com- 

 bine them in the solid picture, which is shown in Plate VIII, Fig. 2, 

 which shows in the foreground the left side of a right-hand individual of 

 Salpa cylindrica, together with that part of the axial tube which pertains 

 to its own body ; and in the background the right side of a left-hand 

 salpa partially hidden. 



Before this figure is described it will be necessary to speak of certain 

 points in which this species differs from all the others I have studied. 



In all the species, this as well as the others, the oral ends of the 

 pharyngeal pouches meet and unite on the middle line at a very early 

 stage to form the oral end of the pharynx, as is shown for Salpa pinnata 

 at 27 and 28 in Plate V, Figs. 2 and 3, and also in Salpa pinnata in 

 Plate XXX, Fig. 3, E'. 



In Salpa cylindrica, as in the other species, this union at the oral end 

 of the pharynx takes place long before the stage shown in Plate VIII, 

 Fig. 2, is reached, and Plate XL shows that they are united, in Figs. 14, 

 16, 17 and 18, 27 and 28, for a left-hand salpa, and in Fig. 21 for a right- 

 hand one. 



The union between the aboral ends of the pouches does not take 

 place quite so soon, but in all the species which I have studied, except 



