AURELIA. 39 



This stage is frequently called the strobila, but there is no 

 definite dividing line between scyphistoma and strobila. The 

 number of discs formed by a strobila seems to be dependent 

 upon conditions, probably largely food supply. 



Before the discs are ready to be detached as ephyrce the 

 tentacles disappear. Ephyra? are detached one at a time from 

 the free end as they mature. 



Up to this point students will be able to determine only part 

 of the points mentioned unless an abundance of material and 

 sections are provided. The remaining points are easily de- 

 termined. 



Examine a free ephyra. If it is alive, watch it swim. Find 

 the mouth, stomach, marginal lobes, marginal lappets, and 

 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, Liicernarw, 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 Scyphomedusae. 

 Jour. Morph., 21,. 1910. 



Mayer: Rhythmical Pulsation in Scyphomedusse. Carnegie Inst. of Wash- 

 ington, 1906. 



