140 BULLETIN 120, UNITED STATES NATIONAL MUSEUM. 



of Opalinids, merely a slender and a stocky form of the one species, 

 with intergrading individuals. 



Cepedea dimicUata shows the usual characteristics of the Cepedeas. 

 the body being somewhat spindle-shaped, with the anterior end not 

 much narrowed but bent to one side, while the posterior part of the 

 body tapers to a rounded point. The endospherules are usually more 

 numerous anteriorly. The very small individuals in the spring tend 

 to be more slender, especially their posterior ends, and the young 

 forms after sexual reproduction, that is, zygotes which have mul- 

 tiplied the number of their nuclei to say four or more, are generally 



Fio. 105. — Cepkdba dimidiata and its foem zblleri, X 117 diameters. Thd outeb 



SIGHT FIGUBBS RBPEESBNT THE ZBLLEKI FOEM. ALL THE INDIVIDUALS DRAWN ABB FROM 

 A SINGLB INDIVIDUAL OF RaNA BSCULBNTA. , 



extremely slender and tapering, almost as much so as a microgamete 

 mother cell. The nuclei are almost all spherical. A few will be 

 found in active mitosis. The number of macrochromosomes seems to 

 be 12. 



SLENDER FORM. 



See United States National Museum Cat. Nos. 16506 and 16507. 



Measurements of an average individual^ of the slender form^ from 

 Rana esculenta. — Length of body 0.18 mm.; width of body 0.0256 

 mm. ; diameter of nucleus 0.004 mm. to 0.0045 mm. ; length of endo- 

 spherule 0.0022 mm.; width of endospherule 0.00125 mm.; cilia line 

 interval, anterior 0.0028 mm., middle 0.003 mm., posterior 0.0033 mm. 



