PORPITA PACIFICA. 337 



partly into the gonostyles, partly into the tentacles." This concept, as Bedot's 

 work has already suggested, is entirely erroneous. In the first place many more 

 than sixteen canals, arranged in two definite series, an inner and an outer, 

 open into the central gastrozooid. These canals are more fully described below, 

 (p. 339) in small specimens. Instead of running meridionally over the lower 

 surface of the centradenia, they enter the formation of the general complex of 

 inferior canals (Plate 29, fig. 4). The gonozooids (except such as are interpolated 

 among the tentacles in the tentacular zone) connect directly with inferior canals, 

 either with ones passing into the deeper regions of the centradenia, or with the 

 network covering its lower surface. And the cavities of the larger gonozooids 

 often connect with two, or even more canals. Furthermore, contrary to Haeckel's 

 views, a study of sections shows that the canals which open into the central 

 zooid never connect with the tentacles except through the medium of the superior 

 canals, a statement agreeing with Bedot's observations on P. umbella. 



The brief account by the latter author of the histology of the superior and 

 inferior canals in P. umbella agrees so closely with the conditions in P. pacifica 

 that I can do no more than substantiate it. But as he did not illustrate it, I 

 add a few figures. The layer of ectoderm underlying the chitinous pneuma- 

 tocyst is composed of flat tile-shaped cells with deep-staining nuclei (Plate 29, 

 fig. 12). Separating this tissue from the entoderm of the superior canals is a 

 well-marked supporting layer. The walls of these canals are composed of several 

 layers of small, round, closely crowded cells, with large nuclei and granular 

 cytoplasmic bodies of a greenish color in formalin material. They do not 

 enclose the colored spherules so characteristic of the superior canals of Velella. 

 Scattered among them, but much fewer in number, are deep-staining cells, with 

 much larger oval nuclei, and fairly large cytoplasmic bodies of irregular outline. 



The walls of the inferior canals are composed for the most part of a single 

 layer of columnar cells, with large cytosomes and small nuclei. Scattered among 

 them there are occasional deep-staining cells with cytosomes resembling those 

 of the deep-staining cells in the walls of the superior canals, but with much 

 smaller nuclei (Plate 29, fig. 14). 



Throughout the courses of the inferior canals the columnar cells frequently 

 contain masses of large dense spherules, reddish brown in formalin material. 

 Near the lower surface of the centradenia the spherules occur in the intercellular 

 spaces as well as within the cytoplasm of the cells. Bedot suggests that the 

 spherules result from a metamorphosis of the small granules which fill the bodies 

 of the small round cells in the walls of the superior canals. But the fact that 



