OCELLATE HYDRO-5IEDUSA. 



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 fifty to three hundred diameters. If 

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

 portion of a specimen which has been preserved in picric 

 acid, as already directed. 



1. Observe that the 

 tentacles (Fig. 22, K 



a, ff, «) are arranged in 

 pairs on the sides of the 

 plane of one of the ra- 

 dial chymiferous 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'a"a"'. Extensile tentacles. 

 /. Sensory bulb. g. Circular 

 chy-miferous tube. h. Radiat- 

 ing chymiferous tube. 



Pig. 22. 



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



B 



