23 6 



COMPARATIVE ANATOMY 



a product of the ectoplasm, but a differentiation of the walls of 

 the alveoli of the cuticular layer. They begin as a number of 

 very fine and rather widely separated fibrillae close underneath 

 the peristomial ring, and run longitudinally down the body 

 towards the stalk. At about one-third of the length of the 

 body from the hinder end the cuticular layer is thickened so 



Fig. 50. 



A, a specimen of I'orticella ntonilata viewed as a transparent object ; 

 , undulating membrane ; g, cytopharynx ; inacr, meganucleus ; 

 mz'cr, micronucleus ; r, reservoir ; c.v., contractile vacuole ; f, food 

 vacuoles ; isc, muscular fibrillae at the base ; c.f., contractile 

 filament. B, another specimen of the same species showing the 

 warty prominences characteristic of the species; and tnic g, a 

 microgamete which has just attached itself. C, a specimen partly 

 retracted to show how the peristome is unfolded over the disc. D, 

 a specimen dividing ; the meganucleus and micronucleus drawn 

 out into nbrillated spindles. , a microgamete of V. nebulifera. 

 (A to D original ; E after Claparede.) 



as to form a ring encircling this part of the body, and the 

 fibrillse appear to be attached to this ring and then to bend 

 rather suddenly inwards, traversing the thickened ectoplasm in 

 the hinder part of the body. Converging together, the fibrils 

 unite where the stalk is joined to the body and are continued 

 into it as the contractile filament. Usually the converging 



