42 MORPHOLOGY OF INVERTEBRATE TYPES 



tseniolas. The tceniola are longitudinal folds of the endodermal 

 lining of the polyp cavity. The four taeniolae are interradial in 

 position and subdivide the cavity of the polyp into four per- 

 radial chambers. Each taeniola has a strong band of longitudinal 

 muscle fibres which are attached to the blind end of the septal 

 funnel. The ectodermal subepithelial muscle fibres are circular. 

 Ephyra. We have seen already that the scyphostoma 

 produces about a dozen ephyrae by a process of strobilization. 

 An ephyra which has just detached itself has a flat body divided 

 into eight narrow lobes or rays, four of which are perradial and 

 four interradial. Each lobe has two end lappets (marginal 

 lappets of various authors. According to Schewiakov they be- 

 come later the sensory lobules of the rhopalia). Between the 

 two lappets is a not yet completely developed rhopalium. The 

 square mouth is situated at the end of a short manubrium. The 

 stomach is subdivided into chambers and gives off eight blind 

 canals, one for each ray. Four interradial gastric filaments are 

 present and their number grows with the growth of the ephyra. 

 The transformation into a medusa is gradual with the more 

 rapid growth of the disc between the lobes, till the star-shaped 

 body assumes the shape of a disc. 



Instructions 



i. Put a mature medusa on its back in a dissecting tray filled 

 with water and examine the specimen with naked eye. Deter- 

 mine the perradial planes by the position of the mouth-arms and 

 the interradial ones by that of the gonads. Find the openings of 

 the subgenital pits. Move the mouth-arms carefully apart with 

 two fingers till the mouth is wide open, introduce then a black 

 horse hair through the mouth into one of the perradial canals, 

 pushing the hair gently till it reaches the circular canal. Intro- 

 duce another hair through a stomach ostium into an interradial 

 canal, and a third hair into an adradial canal. Make a full page 

 drawing showing the following structures: Four mouth-arms 



