PHYLUM TROCHELMINTHES 



125 



greater in later generations. With restoration to normal conditions, 

 however, it disappears within one or two generations. 



Miller (1931) has described the life history of the rotifer Lecane^ 

 which is admirably suited to a study of the alternation of partheno- 

 genetic and bisexual generations. The mictic female rotifer, capa- 

 ble of sexual reproduction, produces small eggs which if unfer- 

 tilized develop into 

 males. The fertilized 

 eggs are larger and pro- 

 duce females. The com- 

 mon type of rotifer 

 female, the amictic^ can- 

 not reproduce by am- 

 phimixis (see page 518). 

 Eggs of the amictic fe- 

 males develop by diploid 

 parthenogenesis (see 

 pages 503 and 505) and 

 produce diploid females, 

 which may be either am- 

 ictic or mictic. In Mil- 

 ler's studies, the length 

 of life of females of 

 Lecane inermis depends 

 to some extent on the Fig. 53. Female producing and male produc- 



Se verity of the process ing eggs of Lecane inermis. Left, the fertilized 

 of egg production. The (female producing) egg of the mictic female. Right,, 

 /■ , J the (female producing) egg of the amictic female. 



\ Bottom, the (male producing) egg of the mictic 



about two-tnirds as female, before the initiation of cleavage. (Courtesy- 

 many eggs as the amictic of H. M. Miller and the Biol. Bull.) 

 and have a longer life. 



Parasitisyn in Rotifers. — Some rotifers (Drilophaga) parasitize 

 worms and some (Seison) parasitize Crustacea. Others are internal 

 parasites found infesting the coelom or the intestine of worms. 



The trochosphere^ or trochophore larvae of the Rotifera, resemble 

 the free swimming larvae of certain annelids. (See page 119.) 



References on Trochelminthes 



HiCKERNELL, L. M. 1917. A Study of desiccation in the rotifer Phi- 

 lodina roseola, with special reference to cytological changes accom- 

 panying desiccation. Biol. Bull., vol. 32, no. 5, pp. 343-407. 



