16 SURFACE FAUNA OF THE GULF STREAM. 
increasing size, they become somewhat more branching, and finally, near the 
outer edge, more or less parallel with the ring of marginal glands, there is 
formed a series of irregular horizontal canals connecting the radiating tubes, 
and forming thus a more or less apparent circular canal (Pl. XII, Figs. 9, 10, 
11), till finally the whole free edge of the mantle is covered by a most intri- 
cate set of anastomosing tubes (PI. XI, Fig. 15). The free edge of the mantle 
terminates by a row of large elliptical glands (Pl. XII, Figs. 4-13; Pl. VIII, 
Fig. 16), the interior of which is filled by fatty, globular cells (Pl. VIII, 
Fig. 17). The whole of the free edge of the mantle is of a beautiful clear 
blue color, with a dark band at the line of contact of the disk and the inner 
seam of the free edge of the mantle, with a darker blue line on the outer 
edge of the glands, both at the exterior and interior edge (PI. VII, Fig. 2). 
The whole surface of the mantle is covered by a close reticulation of irregular 
epithelial cells. 
The smallest (so-called Velella) Rataria examined by Pagenstecher meas- 
ured between 0.8 and 2.25"", and it seems impossible from what I have said 
here regarding the young stages of Velella and of Porpita which I have had 
the opportunity to examine to consider Rataria as anything but the young of 
Porpita, as Burmeister had already done. The young Porpita in its Rataria 
stage passes through an embryonic stage, in which the young Porpita has a 
prominent sail fully as marked as the sail of the corresponding stage in 
Velella. This stage, to a certain extent, recalls strongly Velella. That this 
embryonic character gradually disappears with age, has been shown by 
g 
Pagenstecher ; but the succeeding stages do not lead, as has been supposed, 
to Velella, but to Porpita. At no time in the development of Velella do 
we have any trace of eight compartments arranged round a central chamber. 
We have, it is true, a central chamber; but there are only concentric 
chambers in the earliest stages I have seen; while the Rataria stages figured 
by Pagenstecher * correspond admirably to the young stage of Porpita I 
found at the Tortugas, in which the eight central chambers occupy the greater 
part of the disk, and can, as is well known, still be traced in fully grown 
specimens. 
* Zeits. f. Wiss. Zool., XII., 1863, Pls. XL, XLI, p. 496. 
