GONIONEMUS. 29 



derivation of the medusa as an outpocketing of the wall of the 

 hydranth is evident. 



Make drawings of sections of male and female reproductive 

 organs (medusa buds). 



For comparison, study Pennaria, Margelis, Hydractinia, 

 Clava, and Eudendrium. 



Hargitt: The Early Development of Penneria tiarella. Arch f. Entwick- 



lungsmech.^ 18, 1904. 



Pearse: Reactions of Tubularia crocea. Am. Nat., 40, 1906. 

 Torrey: Biological Studies on Corymorpha. I. Jour. Exp. Zool., 1, 1904; 



II. Univ. Calif. Pub. Zool., 3, 1907. 



GONIONEMUS. 



As has been seen, the medusae buds are usually produced from 

 the walls of a specialized hydranth (Leptomedusae) or from the 

 manubrium wall of an ordinary hydranth (Anthomedusae). A 

 series of these buds in various stages would show the formation 

 of the umbrella-shaped individual with the growth of the marginal 

 tentacles around the edge. The life-history of this form is not 

 known, but from its structure we are led to believe that it 

 belongs to the suborder Leptomedusse. It is found in con- 

 siderable numbers throughout the summer in the border of eel- 

 grass in the Eel Pond at Woods Hole, where it may be obtained 

 with a dip-net. It is more satisfactory to study than the medusa 

 of Obelia, as it is much larger and its movements and organs 

 are more easily observed. In plan of structure the two are 

 quite similar. 



Put a living specimen in a flat-sided jar containing sea-water, 

 or in a finger-bowl, with a black tile beneath, and notice: 



1. Its method of locomotion. To the contraction of what 

 part of the bell is movement due ? How large is the jet of water 

 that is delivered from the bell ? Why is the jet made narrow ? 

 Does the jet necessarily leave at the center or may it be thrown 

 from one side ? Should it be thrown from one side, what would 

 be the result ? 



2. Its position in the water when quiet. Why is this position 



