IIYDROZOA. 85 



The firm horny layer, or polypary, which the 

 coenosarc excretes in Tubularia and its allies, 

 remains in a comparatively rudimentary condition 

 among most other Corynidce. In few, however, 

 is it absent altogether. In Hydractinia, it be- 

 comes elevated at intervals to form numerous 

 rough processes or spines, while over the general 

 surface of the ectoderm its presence is almost im- 

 perceptible. A very different modification is pre- 

 sented by the genus Bimerm. Here the polypary 

 is not, as in other members of the order, restricted 

 to the coenosarc, but extends itself so as to clothe 

 the entire body of each polypite, leaving bare 

 only the mouth and tips of the tentacles. 



The chief differences which prevail among the 

 polypites of the Corynidce have reference either to 

 size or the disposition of their tentacula. The 

 comparatively gigantic polypite of Corymorpha 

 nutans, which attains a length of 4*5 inches, is 

 described by Forbes and Groodsir as presenting 

 the appearance of a beautiful flower, nodding 

 gracefully upon its stem (^fig. 16, a). Another 

 species of the same genus, G. nana, does not 

 exceed '5 of an inch in length, though this, in its 

 turn, is double the size of the tiny Vorticlava 

 huonilis {Jig. 1 7, a). Still more minute are the 

 delicate polypites of some species of Eudendrium. 

 In most members of the present group the general 

 form of the polypite is more or less clavate. 



The tentacles exhibit several distinct modes of 

 arrangement. In Tubularia and Corymorpha a 

 fringe of short appendages immediately surrounds 

 the mouth of the polypite, from the base of which, 

 close to the distal extremity of the coenosarc, arises 

 a second circlet of much longer filiform tentacula, 



G 3 



