GONIONEMUS. 31 



season. The eggs or spermatozoa, as the case may be, are de- 

 hisced from these into the water directly. 



During the breeding season specimens placed in the dark in 

 the latter part of the afternoon and left for two or three hours 

 will shed eggs and sperm. The fertilized egg undergoes cleav- 

 age, a planula is formed that finally attaches at one end and 

 develops, into the hydra stage. Eggs are normally laid about 

 8 P. M. 



6. The tentacles. Is their arrangement a radially symmetrical 

 one? How are the nematocysts arranged on them? Look for 

 adhesive organs on them. Of what use are such organs? 



Turn your specimen with the velum side toward you and 

 study the edge of the medusa with a low-power objective for 

 the sense organs. These are of two kinds : 



(a) The larger, round bodies at the bases of the tentacles 

 communicate with the circular canal (which may possibly be 

 seen along the edge of the bell). They are filled with a layer 

 of strongly pigmented endoderm cells and are probably light- 

 percipient organs. 



(b) Other small sessile and transparent outgrowths, situated 

 between the bases of the tentacles, are the so-called otocysts, 

 which are probably static organs. 



All of the tentacles are abundantly supplied with tactile, 

 sensory cells. There is a well-established circumvelar nerve 

 ring (not easily determined in living material) derived from the 

 ectoderm, also scattering nerve cells beneath the ectoderm in 

 connection with the muscular tissue. Ex-umbrellar and sub- 

 umbrellar layers of muscle fibers are also present. 



Make a drawing from the side, slightly tipped, to show the 

 velum, and another as seen from the oral surface. 



Brooks: Life History of Hydromedusse. Mem. Bost. Soc. Nat. Hist., 3, 



1886. 

 Murbach: The Static Function in Gonionemus. Am. Jour. Physiol., 10, 



1903. 

 Perkins: The Development of Gonionema murbachii. Proc. Acad. Nat. 



Sci., Phila., 1902. 



Yerkes: A Study of the Reaction Time of the Medusa Gonionema murba- 

 . chii to Photic Stimuli. Am. Jour. Physiol., 9, 1903. 



