l82 NUTTING [164] 



writer, Calkins,' has followed his classification quite closely, and 

 includes representatives of what would ordinarily be regarded as 

 at least eleven families in five families as defined by Schneider. 

 It is not likely that classifications will ever represent anything 

 but individual opinion, and it is probable that there will always 

 be two sets of extremists who on the one hand will be too ready 

 to multiply groups, and on the other will be too conservative to 

 recognize real progress. The Hydroida offer unusual difficul- 

 ties and consequently students of that group find agreement, 

 even along the most general lines, practically impossible. The 

 objective point of systematic discussion has been the attainment 

 of a system of classification by which genera could be distin- 

 guished by means of the trophosome alone. This end, although 

 in theory greatly to be desired, appears to be unattainable. The 

 writer has chased this will-o-the-wisp for years, and is ready to 

 abandon its pursuit as unprofitable. Abler men have had the 

 same experience, and it appears to be pretty well established 

 that in practice we must base generic distinctions on the gono- 

 some alone, although the judgment of students will inevitably 

 differ as to the extent to which this can be profitably done. 

 Botanists have encountered the same difficulty in their study of 

 the lower plants, such as the fungi, and have come to the same 

 conclusion. In neither case has nature been working for the 

 convenience of naturalists, and the fact should be accepted 

 without a bootless chase after the unattainable. 



G TMNOBL AS TEA. 

 Hydroida in which well differentiated hydrothecie and gonangia are 

 not present. What might be called ' pseudo-hydrothecae ' are found in 

 some species as in Ejidendrium vaginatum (see description of that 

 species on pages 167-168). 



Family CORTNID^E. 



Trophosome. — Hydranth with a terete body and proboscis and scat- 

 tered capitate tentacles only. 



Gonosome. — Fixed sporosacs, or free medusce with a very long manu- 

 brium, four marginal tentacles and four sense-bulbs with eye-spots. 



'Some Hydroids from Puget Sound, Proc. Bost. Soc. Nat. Hist., Vol. 

 XXVIII, No. 13, 1899. 



