SERTULARTA. GONIONEMUS. 31 



SERTULARIA. 



In habits and relation of parts there is nothing fundamentally 

 different from the other forms studied. The gonosomes present 

 another modification. 



1. The male gonosome has the blastostyle pressed to one 

 side and carries a single gonophore with prominent manubrium 

 and a mass of sperm. The sperm are actually between the 

 ectoderm and endoderm of the manubrium. 



2. The female gonosome has the blastostyle pressed to one 

 side and from it originate one at a time vestigial gonophores 

 that in turn push toward the distal end of the gonangium and 

 discharge their eggs into a specially constructed brood pouch, 

 the acrocyst. By opening acrocysts with needles stages in 

 development up to planulse may be obtained. 



Make a drawing showing a female gonosome with an acrocyst. 



GONIONEMUS. 



This form, belonging to the suborder Leptomedusae, has a 

 much reduced polyp generation. It is found in considerable 

 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 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 

 more desirable than the opposite? With a needle-point prove 

 that various parts of the body are sensitive. 



