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HANDBOOK OF INVERTEBRATE ZOOLOGY. 



partition, which reduces the external opening of the sub- 

 umbrellar cavity to a small circle (Figs. 21 and 25, d). 

 This opening varies in size according to the degree of ex- 

 pansion or contraction of the velum. 



FIG. HI 



FIG. 21. Mnemopsis Bachei (southern variety) drawn from a living 

 specimen, magnified about ten diameters. (Drawn from nature by W. K. 

 Brooks. ) 



a. Umbrella, b. Sensory bulb. c. Velum, d. Aperture of velum. 

 c. Club-shaped tentacles. /. Manubrium. g. Oral tentacles, i. Radiat- 

 ing chymiferous tubes, k. Circular chymiferous tube. I. Reproductive 

 organs, h. Radial tentacles. 



4. The four bunches of radial tentacles (Furs. 21 and 

 25, h) which spring from the lower margin of the umbrella, 

 outside the velum. In the living medusa these tentacles 

 are very extensile, and their length may be equal to or 



