OBELIA, CAMPANULARIA 47 



is characteristic for this form. Notice the quick reversal 

 when the animal swims. The radial canals are easily seen, 

 but the gonads are not developed at the time of liberation. 

 The velum is very small. 



Gonionemus is a more favorable medusa to study. This 

 form is valuable for comparison. 



CAMPANULARIA 



In structure and habits this form is so much like Obelia 

 that it is not easy to distinguish the two genera without 

 studying the gonosomes. Several species are found at Woods 

 Hole, two of which (C ' ampanularia flexuosa and C. calceo- 

 lifera) are usually abundant during the summer. 



The gonosome of one species superficially looks like the 

 gonosome of Obelia, while the other has a notch on one side 

 near its extremity. In structure they are similar. 



The blastostyle runs throughout the length of the gonan- 

 gium and gives rise to buds that develop into imperfect gono- 

 phores. The structure of these gonophores is difficult to make 

 out in fresh material. While they are comparable to 

 medusae, they never become detached, and organs usually 

 present are largely aborted. 



The distinct manubrium of the male gonophore becomes 

 charged with sperm which, as they develop, press the ecto- 

 derm of the manubrium against the ectoderm of the sub- 

 umbrella. Ultimately the ectoderm of the manubrium 

 ruptures and the sperm escapes through the subumbrellar 

 cavity. 



A female gonophore ripens usually one, sometimes two, 

 eggs. The mature egg, which lies -inside the ectoderm of the 

 manubrium, before segmentation is flattened and molded be- 

 tween the mass of the manubrium and the subumbrellar 

 wall. The growth of the egg presses the manubrium to one 

 side. Such an egg appears as a brownish granular mass with 

 a distinct, clear nucleus. The ectoderm of the manubrium 

 ultimately ruptures and liberates the eggs into the subum- 



