358 L. MURBACH. 



hut because the stalks themselves resemble very much the 

 elastic filaments found in nettling batteries. 



In the contracted condition the stalked organs seem to beset 

 the tentacles on all sides, but during expansion they are all 

 directed more or less aborally. The neraatocysts in the stalked 

 organs are developed in the bases of the tentacles, and migrate 

 outward to where the capsules of the stalked organs arise as 

 evaginations of the ectoderm (fig. 14). At such points the 

 ectoderm is already supplied with the hair-like processes which 

 later stand on the capsules. 



When somewhat expanded the stalks are thick and have a 

 wavy outline, while, expanding still more, they look not unlike 

 an unfolding zigzag line or spiral. This gives rise to the 

 granular appearance described by Allman (p. 225), and is in all 

 probability due to optical sections of the joints or spirals of the 

 unfolding stalks. 



Finally, there is a very fine smooth filament, not much thicker 

 than a nettling thread, and about as long as the diameter of 

 the medusa, bearing the quivering capsule on its end. During 

 contraction these several appearances occur in reversed order. 



The capsules (fig. 13) are thick-walled and somewhat wavy 

 in outline, as if they were made up of segments, and are pierced 

 by a number of openings for the emission of the threads from 

 the contained nematocysts. Covering at least two thirds of 

 the outer portion of each capsule are stiff" hairs capable of 

 vibrating so as to impart a peculiar quivering motion to the 

 capsule. They do not wave as cilia usually do, and so can 

 hardly be compared with them. Allman has called them 

 vibratile cilia, and Agassiz ^ does not mention or figure them. 

 The function of the vibratile cilia may be to move the capsules 

 through more space, or may also be tactile. 



As to the identity of our medusa with G em m aria gem- 

 mosa, McCrady, there can be no doubt, and that it agrees as 

 nearly with the European form as with the one figured and 

 described by Agassiz ^ may be attributed to age, sex, and con- 

 dition of expansion of parts. 



' Agassiz, A., '111. Cat. N. A. Acalepha;,' p. 184, 1865. 



