30 CCELENTERATA. 



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 hlastostyle 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 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 rup- 

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

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

 The mature egg, which lies inside the ectoderm of the manu- 

 brium, before segmentation is flattened and molded between 

 the mass of the manubrium and the 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 

 ruptures and liberates the eggs into the sub-umbrellar cavity. 

 Cleavage stages are frequently found, and planuloe, the lar- 

 val stage that is finally set free, may be found. In old gono- 

 somes, where most of the gonophores have matured their 

 sexual products and the outer end of the blastostyle has broken 

 down, especially large planulse may frequently be found. 

 These may be liberated with needles and studied with a high 

 power for ciha and the arrangement of cells. Older planulie 

 will show a streak that indicates the formation of a cavity inside. 

 Planulse of this kind placed in a watch-glass of sea-water 

 and covered to prevent evaporation will soon attach and 

 develop into hydranths. When attached the sea-water should 

 be changed twice a day. Without feeding development is not 

 continued far. 



Make drawings of qpnosomes and of a planula. 



