<)2 Papers from the Marine Biological Laboratory at Tortugas. 



It is shown in dorsal view, magnified 300 diameters in plate 7, figure 

 15. and in ventral view in figure 14. It is deeply rooted in the tail of the 

 adult by a process from the anterior, or oral, end of its body. The process 

 is hollow, as is shown in the sections drawn in figures 24 ami 25 of plate 8, 

 but there is no trace of an opening at its tip, and it no doubt absorbs its food 

 in a liquid state. As the sections show, its wall consists of a single layer of 

 large cells, with here and there a cell or a group of cells on its outer surface. 

 These outer cells seem to be blood corpuscles of the adult. In the body- 

 cavity of the embryo there is a row of four big cells in the axis that passes 

 through the root. One of them is shown in section in plate 8, figure 23. 

 They are no doubt concerned with the nutrition of the embryo, making the 

 food that is taken up by the root available. 



On the middle line of the dorsal surface, near the attached end of the 

 body, there is an opening, shown at / in plate 8, figure 23, which we regard 

 as the mouth. It communicates with a thin-walled, V-shaped chamber, ad, 

 which we regard as the oral or stomod?eal chamber of the pharynx. At 

 each end it opens into one of the large, thick-walled, ciliated branchial 

 pouches of the pharynx, which are shown at t, t, in plate 7, figures 14 and 

 15, in the entire embryo, and in section at t, t, in plate 8, figures 21, 22, and 

 23. In side view of the adult, figure i, the gill is shown, at I, as a thin- 

 walled tube, opening at its inner end into the pharynx through the internal 

 spiracle, which is shown to be ciliated in plate 4, figure 3, at k and /; and 

 opening to the exterior through the external spiracle, which is on the ventral 

 surface near the middle line. In all these respects the embryo that is shown 

 in plate 7. figures 14 and 15, is so much like the adult as to show, beyond 

 question, that it is the embryo of an appendicularian. The ciliated pharyn- 

 geal pouches are shown in figure 15 in dorsal view and in figure 14 in 

 ventral view, at t,.t. The gills are shown, u,u, in ventral view, communi- 

 cating with the pharyngeal pouches at the posterior ends, which are above 

 in the figure and opening to the exterior, near the middle line, through 

 openings that are much more elongated than they are in the adult. 



In the sections in plate 8, figure 23 is most anterior, and it cuts the mouth, 

 /, and the oral region of the pharynx, ad, showing its communication with 

 the pharyngeal pouches, t, t, which are shown in figure 22, communicating, 

 at v, with the gills, u, n, through the internal or pharyngeal spiracles ; while 

 figure 21 shows the external spiracles at ac. 



The large, thick-walled chamber shown at v in plate 8, figures 22 and 

 23, may be the stomach, bilobed at its tip. In plate 8, figures 17 and 18, 

 which are optical sections of the younger embryo shown in plate 7, figures 

 19 and 20, it is shown, at v, communicating with the branchial pouches, t, t, 

 of the pharynx. 



The tissue that occupies the space between the three chambers in figures 

 21 and 22, and which is badly preserved, may perhaps be the notochord and 

 nervous system. 



