28 CCELENTERATA. 



species that differ in the number of tentacles are common at 

 Woods Hole. The inverted bell with the manubrium sticking 

 out from the convex surface of the resting specimen is char- 

 acteristic 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 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 gonangium 

 and gives rise to buds that develop into imperfect gonophores. 

 The structure of these gonophores is difficult to make out in 

 fresh material. While they are comparable to medusse, 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 rup- 

 tures and the sperm escape through the sub-umbrellar cavity. 



A female gonophore ripens usually one, sometimes two, eggs. 

 The mature egg before segmentation, which lies inside the 

 ectoderm of the manubrium, is flattened and molded between 

 the mass of the manubrium and sub-umbrellar 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 



