776 CHARLES L. BOULENGER. 



changed in character and is identical in structure with that 

 covering the hydranth, consisting of large epithelial cells, 

 interstitial nellsj and nematoblasts, with occasional nemato- 

 cysts. 



The independent origin of the four radial pouches of endo- 

 derni is still more obvious in figs. 7, 8, and 9, which are 

 three sections in different planes of a slightly later stage. 

 In the transverse section (fig. 7) the entocodon is seen to be 

 roughly square in section, being in contact with the super- 

 ficial ectoderm at the four corners (interradii) ; the four 

 perradial pouches are thus completely separated from one 

 another. A median longitudinal section (fig. 8) through the 

 perradii at this stage shows, of course, two of the endodermal 

 pouches separated by the hollow entocodon. As pointed out 

 by Goette, it is from the examination of such a section, 

 independently of others of the series, that the idea arose that 

 a double-walled cup of endoderm was formed by the growth 

 of the entocodon, A tangential section taken a short way on 

 either side of this median section will naturally show a single 

 pouch only, as illustrated in fig. 9. In this stage the forecast 

 of the manubrium is already conspicuous, and is, of course, 

 clothed externally by the proximal wall of the entocodon. 



The four endodermic pouches continue their growth out- 

 wards to the very tip of the bud, and at their terminations 

 push out the ectoderm, causing the formation of four perradial 

 bulbous projections, which are the forecasts of the ocellar 

 bulbs. A section, therefore, taken through a perradius gives 

 rise to the false idea of an invagination of ectoderm towards 

 the entocodon (PL 43, fig. 10). The four bulbs are very 

 conspicuous features of the external anatom}^ of the medusa, 

 even at this relatively early stage of development (Text- 

 fig. 4). 



The formation of the endoderm lamella is exactly as 

 described by Goette for Podocoryne carnea; the central 

 part of each endodei'mal pouch becomes a radial canal, the 

 large cells at the edges growing out to form two solid wings 

 of endoderm, which meet similar projections from the other 



