THE OPALINID CILIATE INFUSOEIANS. 



19 



Fig. 6. — PnoTOOPALiNA intestinalis ; 



A MICROGAAIATE. THE ELLIPSOIDAL 

 BODY, UNSTIPPLED, IS THE NUCLEUS. 



X 1,000 DIAMETERS. (After Met- 

 calf, 1909.) 



their own breeding. Here the cysts fall to the bottom, lying there 

 probably for some days, until the eggs of the host species have devel- 

 oped into tadpoles. These tadpoles, browsing along the bottom, 

 ingest the cj'sts along with their algal food. 



Passing through the alimentary canal of the tadpole, the cysts, 

 about four hours after ingestion, hatch in the rectal region (fig. 5, 

 d^ e, /), the little Opalinids reappear- 

 ing in the same condition as that in 

 which they entered the cj'st, except 

 that, first, they have usually extruded 

 most of their ectosarc spherules (fig. 

 5, c), and, second, they often have 

 extruded from their nuclei during the 

 period of encystment some of their 

 chromatin, in the form of from one to 

 four rounded masses, which can be 

 seen for a time in the cj^toplasm, but 

 soon are absorbed (fig. 5, e and /). 

 The little Opalinids now divide sev- 

 eral times, forming ultimately gam- 

 etes of two sorts, macrogametes (fig. 

 7), closely resembling the ordinary forms, except that they are 

 usually uninucleate, and microgametes (figs. 6 and 7), which are 

 slender uninucleated individuals having a slender tapering tail 



devoid of cilia. The tail is bent 

 at the base at right angles to the 

 body, and near its naked tip is a 

 slight swelling forming a minute 

 ball that is sticky. The cilia of the 

 microgamete are sparse and un- 

 usually long for so small an indi- 

 vidual. By their rather feeble lash- 

 ing the male gametes move about 

 backwards, that is, with the pointed, 

 posterior end leading. Upon com- 

 ing in contact with a macrogamete 

 the male attaches itself first by the 

 sticky ball upon its tail. Then it 

 gradually draws into the macro- 

 gamete, becoming completely fused. 

 Its nucleus approaches and meets that of the macrogamete, both being 

 somewhat spindle-shaped (fig. 8, a) , and the two lying diagonally to- 

 gether. Soon the dividing portion of the nuclear membrane disappears 

 (fig. 8,5) and the two nuclei become completely fused (fig. 8, c) . Nere- 



FlG. 7. — PrOTOOPALIXA INTESTINALIS ; 

 COPULATION OF MICROGAMETE AND 

 MACROGAMETE. 



