OCELLATE HYDRO-MEDUSA. 



43 



on a glass slide with a thin glass cover, in a. drop of the 

 dilute glycerine, and examine it with a magnifying power 

 of one hundred and tifty to three hundred diameters. If 

 osmic acid cannot be procured, mount in the same wny a 

 portion of a specimen which has been preserved in picric 

 acid, as already directed. 



1. Observe that the 

 tentacles (Fig. 22, K 



a, a, (i) are arranged in 

 pairs on the sides of the 

 plane of one of the ra- 

 dial cliymiferous tubes. 



The number increases 

 with age, and those near- 

 est the middle are the 

 oldest. 



FIG. 22. Sensory bulb, and 

 bunch of radial tentacles, from 

 a living specimen, magnified 

 about eighty diameters. ( Drawn 

 from nature by W. K. Brooks. ) 



a. Club-shaped tentacles. 

 a'o"ii'". Extensile tentacles. 

 /. Sensory bulb. g. Circular 

 cliymiferous tube. h. Radiat- 

 ing cliymiferous tube. 



PIG. 22. 



2. The pair nearest the median line (Fig. 22, ) are 

 somewhat different from the others. They are shorter, 

 less contractile, and are made up of an enlarged base which 

 carries an ocellus, a slender shaft, and an enlarged, club- 

 shaped terminal portion. 



3. The ocellus at the base of this tentacle is a spherical 

 accumulation of pigment granules, in the centre of which 

 is a transparent, highly refractive spherical lens. 



