12 JOHNS HOPKINS UNIVEKSITY MORPHOLOGICAL MONOGRAPHS. 



cratica, Plate II ; in both the aggregated form of Salpa hexagona, Plate III, 

 Fig. 1, and the solitary form ; in both the aggregated form of Salpa cor- 

 diformis, Plate III, Figs. 2 and 3, and the solitary form, Plate IV, Fig. 

 5 ; in the solitary form of Salpa cylindrica, Plate III, Figs. 5 and 7 ; in 

 the aggregated form of Salpa runcinata, Plate XLIII, Fig. 2, and in the 

 solitary form, Plate XLIII, Fig. 3; and in the solitary form of Salpa 

 africana, Plate IV, Fig. 2, and the careful study of living specimens will 

 undoubtedly show that they exist in most of the species. 



The aggregated form of Salpa runcinata is shown in Plate XLIII, 

 Fig. 3. It has the two serrated ridges on the upper surface, running 

 from the posterior end of the body to the region of the mouth, and it has 

 three more ridges on the lower surface. The lower surface of the solitary 

 form of this species, Plate XLIII, Fig. 2, is so highly ornamented that I 

 should be almost disposed to regard it as a new species, if it did not agree 

 in all other respects with the published descriptions, and had I not found 

 markings of the same sort in so many other species. The arrangement 

 of the serrated ridges in this species is so much like those of Herdman's 

 Salpa echinata that I am almost disposed to believe that this species is a 

 Salpa runcinata. Except for a slight difference in the muscles its 

 internal structure is like that of Salpa runcinata, and I have found great 

 variation in the arrangement of the muscles in all the species of the run- 

 cinata group. 



I have not found the ridges in my specimens of the aggregated form 

 of Salpa cylindrica, Plate III, Fig. 6, but they are well developed in the 

 solitary form and, except that they are not serrated, they are almost 

 exactly as they are in Salpa runcinata. They are shown on the upper 

 surface in Fig. 5, and on the lower surface in Fig. 7. 



The digestive organs of Salpa consist of the pharynx, c, which opens 

 externally through the mouth, r, and communicates through the oeso- 

 phagus, Plate VIII, Fig. 2, q, with the stomach, p, from which the intes- 

 tine, p', runs to the anal orifice, p", by which the intestine opens into the 

 atrium, g'". In most species of Salpa the digestive organs, with their 

 accessory glands, and in the aggregated form the testis also, are bound 

 together into a compact "nucleus," Plate IV, Fig. 2, which is so solid 

 and opaque in the adult that its structure can be studied only by sections. 

 The arrangement of the digestive organs is essentially like Fig. 2 of Plate 

 VIII, however, and those of the solitary salpa are usually like those of 

 the aggregated salpa, 



