378 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



Figure 3, the distal or far side of Figure 2. As this figure was constructed 

 from the same series of sections, it is not reversed, but is shown as Figure 2 would 

 appear when focused upon the far side. 



Figure 4, proximal view of an older stage, showing a left-hand salpa in the fore- 

 ground, and a right-hand one in the background. 



PLATE VII. 



Figure 1, part of the body of the right-hand salpa of Plate VI, Fig. 2, shown 

 more enlarged in distal view. 



Figure 2, a distal view of the left-hand salpa of Plate VI, Fig. 4. 



Figure 3, a proximal view of a left-hand salpa at an older stage. 



Figure 4, a proximal view at an older stage, showing a right-hand salpa in the 

 foreground and a left-hand one in the background. 



Figure 5, the same at a still older stage. 



PLATE VIII. 



1, SALPA PINNATA; 2, SALPA CYLINDKICA ; 3, DOLIOLUM EHRENBERGII ; 4, SALPA 

 COSTATA ; 5, SALPA CORDIFORMIS ; 6, SALPA CHAMISSONIS. 



Figure 1, proximal view of two aggregated specimens of Salpa pinnata. 



Figure 2, proximal view of a right-hand Salpa cylindrica in the foreground and 

 a left-hand one in the background, at the stage shown in Plates XXXIX and XL. 



Figure 3, the tailed larva of Doliolum Ehrenbergii at an advanced stage, to show 

 the degeneration of the chorda, and the formation of a caudal vesicle or eleoblast. 

 From Uljanin, Doliolum, Taf. 5, Fig. 1. 



PLATE IX. 

 SALPA HEXAGONA. 



(Figure 12 was drawn with a Bausch and Lomb one-eighth objective and B eye- 

 piece. All the other figures were drawn with Zeiss D objective and A eyepiece.) 



Figures 1 to 10 represent a series of sections through an egg at an early stage of 

 segmentation, cut at right angles to the fertilizing duct. Figure 1 is the fifth section 

 in the series ; Figure 2 the seventh ; Figure 3 the eighth ; Figure 4 the ninth ; Figure 

 5 the tenth ; Figure 6 the eleventh ; Figure 7 the fourteenth ; Figure 8 the eighteenth ; 

 Figure 9 the twenty-fifth, and Figure 10 the thirtieth. 



Figure 1 is proximal or nearest to the next younger egg in the series, and Figure 

 10 is distal or nearest the next older egg. 



Figure 11 is a section in a plane at right angles to the plane of the sections shown 

 above. It is from an egg at the stage which is shown in Plate X, Figs. 4 and 5. 



Figure 12 is a more enlarged view of a portion of the embryo which is shown in 

 Plate XI, Figs. 1 and 2, but the drawing was made from a section intermediate 

 between those which are shown in the figures. 



PLATE X. 

 EARLY STAGES IN THE EMBRYOLOGY OF SALPA HEXAGONA. 



(All the figures were drawn with a Bausch and Lomb one-eighth, and were 

 reduced one-half in the process of photographic reproduction.) 



Figure 1, a section transverse to the fertilizing duct, x, of a ripe unfertilized egg. 



Figure 2, a section in the same plane as Figure 1, through an egg at the time of 

 fertilization. The head of the spermatozoon is shown just inside the egg. 



