136 THE BIOLOGY OF HYDRA : 1961 



er this central configuration. It may, then, constitute one more 

 variation from the basic pattern of filament arrangement in flagella 

 and cilia. The dense granules (G) resemble closely the granules 

 considered by Slautterback and Fawcett ( 12 ) to be glycogen. 



SUMMARY 



Electron microscopy of ultrathin sections of osmium-fixed and 

 Epon-embedded intact Hydra have revealed several new aspects 

 of stenotele fine structure. The internal tubule possesses an en- 

 larged head containing dense granules which may represent a por- 

 tion of the venom. The head has an extension ending in a hook. 

 The spines are seen to posses a bulbous enlargement at their 

 attachment to the invaginated capsular wall. Invaginated capsular 

 wall material showed a 160 A periodicity, possibly supporting the 

 belief that nematocyst capsules contain protein related to the 

 collagen family of proteins. A relationship is suggested between 

 centrioles and cnidocils (because of the similarity in appearance 

 of these two structures), thus extending the centriole— cilia, flagel- 

 la relationship. 



REFERENCES 



1. Bennett, H. S. 1960. Personal communication. 



2. Bouillon, J., P. Castiaux, and G. Vandermeerssche. 1958. Structure submicro- 



scopique des cnidocils. Bull. micr. appl., 8: 61. 



3. Chapman, G. B., and L. G. Tilney. 1959. Cytological studies of the nemato- 



cysts of Hydra. I. Desmonemes, isorhizas, cnidocils, and supporting struc- 

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4. Chapman, G. B., and L. G. Tilney. 1959. Cytological studies of the nemato- 



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