TIG. 72. -Vorticella. 



A, living specimen fully expanded, showing stalk (st) with axial fibre (ax. /), 

 peristome (per), disc (d), mouth (milt), gullet (g#), and contractile vacuole 

 (c. vac), (x 250.) 



B, the same, bent on its stalk and with the disc turned away from the observer. 



C, optical section of the same, showing cuticle (cu), cortex (cort), medulla (med), 

 meganucleus (nil}, gullet (gull), several food vacuoles and anal spot (an), as 

 well as the other structures shown in A. 



D 1 , a half-retracted, and D 2 a fully-retracted specimen, showing the coiling of the 

 stalk and overlapping of the disc by the peristome. 



E 1 commencement of binary fission ; E-, completion of the process ; E :! , the 

 product of division swimming freely in the direction indicated by the arrow. 



F', a specimen dividing into a megazooid and several microzooids (m) ; F 4 -, 

 division into one mega- and one micro-zooid. 



G 1 , G'^, two stages in conjugation, showing the gradual absorption of the micro- 

 gamete (m) into the megagamete. 



H 1 , multiple fission of encysted form, the nucleus dividing into numerous masses ; 

 H 2 , spore formed by multiple fission; H<* H7, development of the spore H* is 

 undergoing binary fission. (From Parker's Biology: E H after Savile-Kent.) 



