122 Mr. C. C. Nutting on the 



original type of the liydranth ; and that the present hydranth 

 is really a very highly specialized sarcostyle. 



As before indicated, the sarcostyles often precede the hy- 

 dranths in the development of the colony, and would thus 

 appear to be an older structure in phylogeny. 



I was unable to confirm Merejkowsky's statement that the 

 extensible part of the sarcostyle was composed of ectodermal 

 cells immersed in free protoplasm. Indeed, it appears that 

 no other author has been able to demonstrate this certainly 

 unique and surprising arrangement. Neither could I find 

 the muscle-bundles and ganglionic cells of von Lendenfeld, 

 although this purely negative evidence should not be allowed 

 to have much weight. The adhesive cells were found in 

 several species of Aglaophenia, and observed in action ; the 

 observations confirm very decidedly the description given by 

 their original describer, von Lendenfeld. 



There has been considerable discussion conceruino; the 

 probable use of the sarcostyles. My own observations on the 

 living organisms would indicate that they serve several 

 distinct functions. 



1st. Defence. — In many cases, especially in the genera 

 Aglaophenia, Lytocarpus, and Cladocarpus, the distal part of 

 the sarcostyle contains a battery of very large and formidable 

 nematocysts or stinging-cells. The threads of these cells are 

 projected all together when a large or dangerous enemy 

 approaches too near the adjacent hydranth. It is probable 

 that the cnidocils of these nematocysts must be touched before 

 the battery is discharged. Some species of Lytocarpus have 

 such effective batteries that their sting is severely felt through 

 the human cuticle, a very unusual thing among the Hydroida. 

 The nematocysts themselves do not leave the nematophores 

 when their threads are projected. 



2nd. Prehension of food. — This is effected by the adhesive 

 cells, which are situated on the extensible part of the sarco- 

 styles of many species. Von Lendenfeld gives an excellent 

 description of the capture of small crustacean zosea. From 

 his account it appears that the prey is first paralyzed by the 

 nematocysts in the tentacles of the hydranths, and then 

 secured by the adhesive parts of the adjacent sarcostyles, 

 which stick firmly to the smooth chitinous covering of the 

 crustacean. After this attachment is formed, the contraction 

 of the sarcostyle brings the victim again within the reach 

 of the tentacles, which convey it to the mouth of the hydranth. 



3rd. The removal of refuse or decomposing organic matter. — 

 This function of the sarcostyles has been suggested by several 

 writers. I have on many occasions noted that the sarcostyles 



