EXPLANATION OF PLATES. 377 



PLATE IV. 



1 AND 7, SALPA SCUTIGERA : 2, SALPA AFRICANA ; 3, 5 AND 6, SALPA CORDIFORMIS ; 



4, SALPA COSTATA. 



Figure 1, part of a fully grown chain of Salpa scutigera. 



Figure 2, a fully grown solitary Salpa africana. 



Figure 3, a young Salpa cordiformis, magnified ten diameters. 



Figure 4, a solitary Salpa costata, about half the natural size. 



Figure 5, a fully grown Salpa cordiformis, enlarged three diameters. 



Figure 6, part of a chain of Salpa cordiformis, enlarged five diameters. 



Figure 7, an advanced embryo of Salpa scutigera, enlarged twenty diameters. 



PLATES V, VI AND VII. 

 SALPA PINNATA. 



In Plates XV, XXIII-XXXIII and XXX VI-XXX VIII, a series of sections of 

 successive stages in the development of the aggregated Salpa pinnata, cut in planes 

 which are parallel to the long axis of the stolon and transverse to the bodies of the 

 salpae, is shown. 



Another stolon was cut into a series of sections at right angles to those in these 

 plates, but in order to diminish the number of figures, I have, instead of figuring all 

 these sections, superimposed their outlines with a camera, and combined them to 

 form the solid pictures which are shown in Plates V, VI, VII, and Fig. 1 of Plate VIII. 



In these figures the numbers at the ends of the cross lines refer to the figures of 

 sections which correspond, or nearly correspond, to the part of the solid picture which 

 is crossed by each line. The correspondence betVeen the two sets of figures is not 

 exact, for the salpse change so rapidly during their development, that the successive 

 stages that are exhibited by one stolon may correspond to the unrepresented inter- 

 vals between the successive stages in another stolon. I have not been so fortunate as 

 to find two well preserved and perfect stolons which are exactly alike, but in those 

 which are figured the departure from exact agreement is not very great, nor is it of 

 such a character as to perplex the reader. 



PLATE V. 

 SALPA PINNATA. 



Figure 1, a proximal or dorsal view of the rudiment of a single salpa in its pri- 

 mary or morphological position. 



Figure 2, a proximal or dorsal view of a right-hand salpa, at the stage where the 

 morphological middle line of the oral end of the body begins to move outwards. 

 The oral ends of the right and left pharyngeal pouches, 27 and 28, have met on the 

 middle line, distal or ventral to the ganglion's, although each still retains its com- 

 munication with the endodermal tube d' of the stolon. 



Figure 3, a dorsal view of an older right-hand salpa. The oral portion of the 

 left pharyngeal pouch, 28', has lost its connection with the aboral portion, 28, and 

 has united behind the ganglion with the oral end of the right pouch, 27. 



Figure 4, a dorsal view of a left-hand salpa, a little more advanced. 



PLATE VI. 



(The reference lines which are marked XXIII in Fig. 3 thould be marked XXXIII.) 



Figure 1, proximal or dorsal view of a right-hand salpa a little older. 

 Figure 2, a right-hand salpa in the foreground, and in the background a left-hand 

 salpa partially hidden. Both are shown in proximal view. 



