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. tiarella 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 I Jind 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 PI. 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. 



