52 



BULLETIN 120, UNITED STATES NATIONAL MUSEUM. 



endospherule 0.001 mm.; cilia line interval, anterior 0.0023 mm., 

 middle 0.0037 mm., posterior 0.0037 mm. 



Some individuals of the intermediate forms of ProtoopaliTia 

 caudata quite closely resemble P. intestinalis in form, lacking a 

 definite spinelike process. But the posterior end of the body, even 

 in these individuals, is usually more pointed, less rounded, than in 

 P. intestinalis. Protoopdlina intestinalis in general is somevs^hat 

 more slender than P. caudata, except the form of the latter which 

 we have called attenuata and the latter have the posterior part of the 



d e f g 



Fio. 27. — Peotoopalina intestinalis^ from bombina bombina ; a, in an anaphase ob" 



MITOSIS ; 6, ANAPHASE N0CLEI FROM A DAUGHTER CELL ; C, ENTERING UPON MITOSIS ; 

 A, IN TRANSVERSE FISSION ; e, AN ORDINARY INDIVIDUAL ; f, AN INDIVIDUAU ENLARGED 

 PREPARATORY TO FISSION, THOUGH THE NUCLEI HAVE NOT YET ENTERED UPON MITOSIS ; 

 g, AN ORDINARY INDIVIDUAL FROM A DIFFERENT HOST. tt TO C MAGNIFIED 460 DIAMETERS ', 

 d TO fir MAGNIFIED 117 DIAMETERS. 



body more gradually tapering and more slender than P. intestinalis. 

 In almost all infections there will be some individuals showing some 

 nuclei in active mitosis. By counting the chromosomes in some of 

 these Avhich are in an anaphase condition the species can be deter- 

 mined confidently. P. intestinalis has eight macrophromosomes ; 

 P. caudata has six. P. intestinalis is the larger, but of course, in 

 the spring, at the time of active division, the individuals of all species 

 become small. One not very familiar with the Opalinids may find it 

 difficult to distinguish at a glance P. intestinalis from P. caudata. 

 Attention should be paid to the larger size, the somewhat more 

 slender form, the rounded posterior tip of the body, and if possible 

 to the chromosome number. 



