16 SURFACE FAUNA OF THE GULF STEEAM. 



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 formhig 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. XII, Fig. 13). 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 latty, 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 (PL VII, Fig. 2). 

 The whole surface of the mantle is covered by a close reticulation of irregular 

 epithelial cell.s. 



The smallest (so-called A^elellie) 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 Poi-pita 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 

 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, XIL, 1863, Pis. XL, XLI, p. 496. 



