The Pelagic Tunicata of the Gulf Stream. 91 



O. intermedia, as described by Lohmann (Appendicularien der Plankton- 

 Expedition, von Dr. H. Lohmann. Ergebnisse der Plankton-Expedition der 

 Humboldt-Stiftung. Bd. II. C. c. Edited by Victor Hensen, 1894) are 

 slight. The tail is like that of 0. longicauda, lacking the fin-like lobe that 

 is described and figured in O. intermedia by Lohmann. In other respects 

 it is like 0. intermedia resembling it, and differing from 0. longicauda, 

 in the following respects : The digestive organs are less compact than in 

 O. longicauda and like those of O. intermedia. The cesophagus joins the 

 left lobe of the stomach much anterior to the curved process that forms 

 the posterior end of the left lobe, as in O. intermedia (see plate 5, figs. 

 7 and 8), and not close to it, as in O. longicauda. The endostyle is near 

 the mouth and nearly vertical, as in O. intermedia, and it is separated from 

 the region of the gills by a wide interval, while it is more nearly horizontal 

 and farther back in 0. longicauda. The thin membranous veil (Schleier) 

 that Lohmann describes and figures in O. longicauda, overhanging the dorsal 

 surface of the posterior end of the body, to which it is attached near the 

 reproductive organ, is not present in any of our specimens, nor does Loh- 

 mann mention it in O. intermedia. 



NOTES ON EMBRYOLOGY. 



In plate 7, figure 13, part of the tail of Oikopleura tortugensis is shown 

 magnified 43 diameters. Attached to it are three eggs, r, r, r, of which one 

 is shown, more magnified in figure 16, and an embryo, s, which is shown, 

 more enlarged, in figures 19 and 20. The eggs are attached to the tail by a 

 process that penetrates into the tissues. In figure 16 one of the eggs is 

 shown, magnified 200 diameters. The opaque egg, r, is inclosed in a 

 follicle, z, of elongated cells with flat outer ends. At the bottom of the 

 figure the fastening process or root, x, is shown. It is formed of follicle- 

 cells, and shows indications of an axial cavity. Xo test-cells can be made 

 out between the yolk and the follicle, the minute, badly preserved speci- 

 mens not being favorable for observation. All of the specimens were fixed 

 with picro-acetic fixative and carefully preserved with changes of alcohol; 

 but as they were preserved for the identification of the species, with no 

 thought of eggs or embryos, they were not isolated, but were handled 

 wholesale as they were collected. While we found several eggs, we found 

 only two embryos in our collection. While they are much better preserved 

 than the eggs, they are too few to afford much information about the details 

 of the life-history. One of them, shown at ^ in figure 13, is shown, magni- 

 fied 300 diameters, in plates 7 and 8, figures 17, 18, 19, 20. An older one 

 is shown in ventral view in plate 7, figure 14, in dorsal view in figure 15, 

 and in sections in plate 8, figures 21, 22, 23, 24 and 25. The structure 

 of the older embryo has features of resemblance to an adult appendicu- 

 larian, and as it is, therefore, more intelligible than the younger one, it 

 will be described first. 



