340 PORPITA PACIFICA. 



with open lumen, but Woltereck's observations show that this is a secondary 

 condition, for in his larva of Velella these eight first-formed points of communi- 

 cation are represented at first by solid entodermal strands (: 04, taf. 19, fig. 18, 

 K), just as are the communications of the outer series of ostia in our specimens. 

 As yet there is no differentiation betw^een the cell elements composing the walls 

 of the superior canals and the trunks connecting them with the gastric ostia. 



In a specimen 4 mm. in diameter, with eleven circular chambers, the gastric 

 ostia of the outer series have increased to about thirty-two, with a corresponding 

 increase in the branching of the superior canals. Furthermore in most instances 

 the connections between the ostia and the latter are by means of open canals, 

 no longer direct but in a network joining the gonozooids on one hand, and the 

 superior canals on the other. The connection, too, between the eight ostia 

 of the inner .series and the superior canals, is now indirect, by a network which is 

 only slightly less complex than it is in the adult. 



Histologically as well as morphologically, superior and inferior canals can 

 now be separated. In both, the walls are composed of a single layer of cells 

 of two kinds, the first and most numerous, columnar, with granular bodies, the 

 second, small, deep-staining, irregular in outline. In the cells of the inferior 

 canals there occur the large dense spherules, often in masses, which give the 

 characteristic reddish brown color to the lower portion of the centradenia in 

 the adult. But as yet, no crystals have been formed, though they are present 

 in specimens but slightly larger (7 mm.). 



Pneumatophore. The smallest specimen is intermediate with respect to this 

 structure between the "Discalia" and "Disconalia" stages described by Haeckel, 

 "Discalia" having one, the "Albatross" specimen five, and "Disconaha" seven 

 circular chambers. Radial sections of this example (Fig. B) and of the individual 

 of 4 mm. show that there are no radial chambers here, any more than there are 

 in the adult. On the contrary the eight stigmata of the innermost circle open 

 into the first circular chamber, just as they do in Porperna (p. 327). Surface 

 views of this region are deceiving, because owing to the partial enclosure of the 

 central by the first circular chamber, these eight stigmata appear to open into 

 the former, while the eight ridges on the "ceiling" of the pneumatosaccus 

 appear to divide it into eight compartments. In these stages, all the stigmata 

 are open. I have not been able to determine at what age the central ones 

 become closed over. 



Before closing this description I may mention two features, interesting 

 though of less importance than the preceding. These are the limbus and the 



