48 COELENTERATA 



brellar cavity. Cleavage stages are frequently found, and 

 planulae, the larval stage that is finally set free, may be 

 found. In old gonosomes, where most of the gonophores have 

 matured their sexual products and the outer end of the blas- 

 tostyle has broken down, especially large planulae may fre- 

 quently be found. These may be liberated with needles and 

 studied with a high power for cilia and the arrangement of 

 cells. Older planulae will show a streak that indicates the 

 formation of a cavity inside. 



Planulae of this kind placed in a watch glass of sea water 

 and covered to prevent evaporation will soon attach and de- 

 velop into hydranths. When attached the sea water should 

 be changed twice a day. Without feeding, development is not 

 continued far. 



Make drawings of gonosomes and of a planula. 



SERTULARIA 



In habits and relation of parts there is nothing funda- 

 mentally different from the other forms studied. The gon- 

 osomes present another modification. 



1. The male gonosome has the blastostyle pressed to one 

 side and carries a single gonophore with prominent manu- 

 brium and a mass of sperm. The sperm are actually be- 

 tween the ectoderm and endoderm of the manubrium. 



2. The female gonosome has the blastostyle pressed to one 

 side and from it originates, one at a time, vestigial gono- 

 phores that in turn push toward the distal end of the gonan- 

 gium and discharge their eggs into a specially constructed 

 brood pouch, the acrocyst. By opening acrocysts with 

 needles stages in development up to planulae may be ob- 

 tained. 



Make a drawing showing a female gonosome with an acro- 

 cyst. 



GONIONEMUS 



This form, belonging to the suborder Leptomedusae, has 

 a much reduced polyp generation. It is found in considerable 



