METRIDIUM. 41 



sense organs. Use these as landmarks to determine the rela- 

 tion of parts to the adult. Are there any outgrowths from the 

 stomach? Do the sense organs have any relation to branches 

 from the stomach? Can you find gastric filaments? 



From the shape of the mouth determine which of the lobes 

 are per-radial and which inter-radial. What part of the adult 

 is represented by the notches between the lobes? 



Study a somewhat older ephyra and find the starting of the 

 ad-radial canals and the beginning of the formation of ad- 

 radial cushions. Examine a series of older stages and find how 

 the ad-radial cushions expand, how the canals branch, and how 

 the circular canal is formed. 



Make drawings of the stages. 



By way of comparison, examine demonstrations of Cyanea, 

 Dactylometra, Lucernarixi, or other forms belonging to this group. 



Hargitt: Variations among Scyphomedusae. Jour. Exp. Zool., 11, 1905. 



Hargitt, C. W. and G. T.: Studies in the Development of Scyphomedusse. 

 Jour. Morph., 21, 1910. 



Mayer: Rhythmical Pulsation in Scyphomedusae. Carnegie Inst, of Wash- 

 ington, 1906. 



ACTINOZOA. 



METRIDIUM. (Sea-Anemone.) 



Specimens are quite common on piles, as well as on rocky 

 bottoms, and may be easily observed by means of a glass- 

 bottomed pail. Most of the observations can be made much 

 better on specimens in aquaria, but it is desirable to see their 

 natural surroundings. 



Specimens for laboratory study should be placed in aquaria, 

 and left undisturbed until they are fully expanded. In experi- 

 menting be very careful not to overstimulate. 



1. Notice the shape and attachment of expanded, living 

 specimens in an aquarium, or in a deep finger-bowl. The free 

 end, called the disk or ^peristome, is fringed with tentacles, and 

 the elongated mouth is located in the middle of this area. At 

 one or both angles of the mouth the lips are thickened into 

 what is called a siphojioglyph. 



