KlG. 72. — I'orticclla. 



A, living,' -^pecinien fully expanded, showing stalk {,sf) with axial fibre {ax./), 

 peristome {per)^ disc ((/), mouth {mtk), gullet (^)^//), and contractile vacuole. 



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



C, optical section of the same, showing cuticle (c 11), cortex {cort ), medulla {ii/cd), 

 nucleus {nu), gullet {gull), several food-vacuoles. and anus {an), as well as the 

 structures shown in A. 



1)1, a half-retracted and D^ a fully-retracted specimen, sho\v-ing the ceiling of the 

 stalk and o\'erlapping of the disc by the peristome. 



E^, commencement of binary' fission ; E-, completion of thu process ; E-', the 

 barrel-shaped product of div'ision swimming freely in the direction indicated 

 by the arrow. 



F^, a specimen dividing into a niegazooid and several microzoolds (/«) ; F-, 

 division into one mega- and one micro/ooid. 



Gi, G-, two stages in conjugation showing the gradual absorption of the micro- 

 gamete (;«) into the megagamete. 



HI. multiple fission of encysted form, the nucleus dividing into numerous masses ; 

 H"-^, spore formed by multiple fission ; H^— H", development of the spore ; H^ is 

 imdergoing binarj' lission. (l*"roMi Parker'^ J->!oloi;y\: V\— H after Saville Kent. 



