382 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



PLATE XVII. 



Figures 1, 2, 3, and 4 are described in the explanation of Plate XVI. 



Figure 5 is described in the explanation of Plate XII. 



Figures 6 and 7 : two stages in the formation of the cloacal aperture of the embryo 

 of Salpa pinnata ; Fig. 6, from the embryo, shown in Plate XXXV, and Fig. 7, from 

 an older embryo. 



PLATE XVIII. 

 A SERIES OF TRANSVERSE SECTIONS PROM AN EMBRYO OP SALPA PINNATA, A LITTLE 



YOUNGER THAN THE ONE SHOWN IN PLATE XLI, FlG. 2. 



Figures 1 to 7 : vertical transverse sections. 



Figure 8 : vertical longitudinal section. 



29, migrating follicle cells from the roof of the placenta. 



PLATE XIX. 



A SERIES OF HORIZONTAL SECTIONS FROM AN EMBRYO OF SALPA PINNATA, A LITTLE 



YOUNGER THAN THE ONE SHOWN IN LONGITUDINAL SECTION IN PLATE XXXV. 



Figure 1 is a section in the plane of the gill, o, and oesophagus, g. 



Figure 2 is a section which passes through the ganglion, s. 



Figure 3 is a section through the subneural gland, t, and the opening of the 

 endodermal tube, d', of the stolon into the pharynx, c, between the halves of the 

 endostyle, d, d. 



Figure 4 passes through the eleoblast, A;, and the endodermal tube of the stolon, d'. 



Figure 5 passes through the germinal mass, and cuts the endodermal tube of the 

 stolon below its opening into the pharynx. 



Figure 6 shows the heart, c, of Fig. 1, more enlarged. 



Figure 7 is a mass of follicle cells from a section between 2 and 3. 



Figure 8 is the heart of Figure 2. 



Figure 9 is the eleoblast, fc; the pericardium,/; the heart, c, and the endodermal 

 tube, d', of Fig. 3. 



Figure 10 is the same region of Figure 5. 



PLATE XX. 

 LONGITUDINAL AND TRANSVERSE SECTIONS OF YOUNG STOLONS OF SALPA PINNATA. 



All the figures were drawn with a Bausch and Lomb J objective and A eye- 

 piece, and they have been reduced one-half in photolithography. 



Figs. 1, 2, 3 and 4 are reversed, as the pericardium, /, is actually on the right side 

 of the stolon instead of the left. 



Figures 1, 2, 3 and 4, transverse sections in a series from an embryo at about the 

 stage shown in Plate XIX and in Plate XLI, Fig. 4. 



Figure 1 is the fifth section in the series ; Fig. 2 is the ninth ; Fig. 3 is the four- 

 teenth, and Fig. 4 the twenty-third. Figs. 5, 6 and 7 are longitudinal sections of very 

 young stolons, and Fig. 6 is the youngest ; Fig. 5 next, and Fig. 7 oldest. Fig. 7 is 

 from an embryo at the stage shown in Plate XXXV. Fig. 5 is shown very highly 

 magnified in Plate XLI, Fig. 7. 



REFERENCE LETTERS FOR PLATES XX AND XXI. 



a, ectoderm of the embryo, a', ectoderm of the stolon, a", layer of ectoderm 

 reflected to form a sheath around the base of the stolon, b, endoderm of pharynx of 



