8 THE HYDROIDS. 
from the Zostera, are black ; the remainder is horn color. The stem in the, 
wharf specimens is horn color throughout. The filiform tentacles in the’ 
Zostera specimens are longer than those of the wharf specimens. The 
swollen distal ends of the capitate tentacles are often larger than those of 
the wharf specimens. I find that Professor Hargitt’ in 1900 called atten- 
tion to certain differences in these two forms of P. tiarel/a at Woods Hole. 
He says that the form upon the eelgrass “matures with much greater 
rapidity and has apparently a much briefer period of activity, hardly covering 
more than about four or five weeks. It is further distinguished by a higher 
coloration of the colonies and of the medusae. Again, the medusae free 
themselves with much greater frequency and ease, and swim much more 
actively. The ova of the two forms likewise show the same difference of 
coloration, those of the [eelgrass] being a brighter orange and much more 
conspicuous, while those of the [wharf] are of a creamy white, with the 
slightest tint of dull pink.” 
From an examination of the capitate tentacles of many hydranths of 
P. tiarella 1 find no exception to a regular arrangement in verticils in the 
younger state, but in the fully developed hydranths with a larger number 
of capitate tentacles there appears an irregular arrangement, especially in 
the proximal region nearest to the filiform tentacles. (See Pl. 4.) 
Hargitt has pointed out that Allman founded the genus Halocordyle on 
the untenable basis of a verticillate arrangement of the tentacles, separating 
P. tiarella on that ground from P. gibbosa, in which they are described as 
irregularly arranged. In addition to what I have said above in regard to 
the arrangement of the capitate tentacles in the young and old hydranths, 
I would call attention to Pl. 2 fig. 5, a camera lucida drawing from the 
type specimen of P. gibbosa which shows the distal capitate tentacles ar- 
ranged in two verticils. Comparing this with the figures of P. tiarella, it 
seems probable that in both the distal capitate tentacles are the first to 
appear, the more distal row first of all, and that later a more or less irregu- 
lar arrangement of the complete number obtains. These observations 
re-enforce the view expressed by Hargitt that the “intergradations in all 
degrees in species from different regions and from the same region” leave 
no basis for the genus Halocordyle. 
1 American Naturalist, 34, p. 387. 
