RHODALIIDAE. 313 



I have been unable to decide definitely whether or not there is an excretory 

 pore connecting the cavity of the aurophore with the exterior. As already 

 noted there is one papilla on the surface which may indicate the presence of a 

 porus; and conditions in Physophora on the one hand and Dromalia on the 

 other, make the presence of such an opening not unlikely. 



Nectosome and siphosome. The pericystic space, as noted above (p. 309), 

 expands below the pneumatosaccus to form an extensive hypocystic chamber 

 which extends downward to the level where nectosome joins siphosome (Plate 

 21, fig. 7). The walls of the cavity dififer in the different planes; on both 

 ventral and dorsal surfaces they are thin, and smooth internally; but on the 

 two lateral faces their inner surfaces are thrown into numerous transverse hori- 

 zontal ridges (Plate 22, fig. 6). The walls are traversed by a loose network of 

 canals communicating on the one hand with the muscular nectophore-plates, 

 on the other with the hypocystic cavity. Basally this chamber communicates 

 with the network of canals which ramify throughout the semicartilaginous sub- 

 stance of the solid siphosome (Plate 21, fig. 7). The number of canals opening 

 into the large chamber has not been determined; probably it is variable. 

 The network is much more extensive in Angelopsis than in Dromalia; its 

 component canals branch and rebranch irregularly, and most densely near the 

 surface where the vascular system communicates with the cormidia. Although 

 the canals vary in size, there is no one which can be identified as the primary 

 central canal of Haeckel. The entoderm layer lining the canals is, of course, 

 continuous with the entoderm of the pneumatocodon. 



Aurophore and zone of proliferation in the Rhodaliidae. The description by 

 Haeckel ('88b) of his order Auronectae, and his detailed, but, as has since been 

 proved, largely erroneous account of the aurophore, has given rise to a great 

 deal of discussion. The improbability that the aurophore was a peculiar Medu- 

 soid, as Haeckel suggested, was pointed out at once by Claus ('89, p. 14), who 

 remarked that such a structure would hardly be developed on the side of the 

 pneumatophore opposite to the zone of proliferation — i. e. on the dorsal sur- 

 face. Haeckel himself was not very confident that his explanation of the auro- 

 phore as a Medusoid was correct, for he suggests ('88b, p. 284) that "it is 

 possible that it was originally only a secondary organ of the pneumatophore a 

 basal apophysis of the air funnel." Chun ('97b) has pointed out that its 

 dorsal location made the latter supposition improbable, according to his view 

 untenable. And in the endeavor to account for the aurophore he offered the 



