THE OPALINID CILIATE INFUSORIANS. 



51 



Stevenson's description in full is as follows: • 



Nptotherus cordiformis and a Balantiditim are both common, but instead 

 of Opalina we have another organism something of tlie same class though it 

 differs in its nuclear arrangement. The largest specimens of this are about 80/t 

 by 60^, while the smallest are about 60ja by 16^. They are covered by cilia 

 of a uniform length, have no apparatus for ingestion or egestion, and the 

 nucleus usually consists of two pear-shaped bodies connected by a definite 

 narrow strand. Up to the present I have not identified tliis. It is character- 

 ized by having a definite spine at one end, especially in the smallest and middle- 

 sized forms. 



Fig. 'Za. — Protoopalixa stevensoni, X 450 diameters. (After Stevenson.) 



All of Stevenson's drawings of this form are given in the accom- 

 panying figure 26. Close relationship to P. caudata is very evident. 

 In my abundant material from Bufo regularis I was not fortunate 

 enough to find these animals. 



PROTOOPALINA INTESTINALIS (Stein). 



IIHtrudo intestinalis Bloch (1782), 

 " Flirrvnierwalzen" Leucophra, Goze (1782), 

 Bursaria intestinalis Ehrenberg (1831), 

 Opalina intestinalis Stein (1856). 



The general description of a Protoopalina, in Section 2 of this 

 paper, is based upon P. mtestinalis. To this must be added some data. 



Hosts. — Bomhina hombina (Linnaeus) \^B ovibinator igneus Lau- 

 renti] and Bonibina 'pachyfci (Bonaparte) \BonribinatOT pachyjms 

 Bonaparte], from central and southern Europe. It is also reported 

 from Discoglossus pictus Otth, Pelobates fuscus (Laurenti), Rana 

 esculenta (Linnaeus), Uperoleia viarniorata Gray, and Tnturus vul- 

 garis (Linnaeus) \Tntoii taeniatus Schneider], but it would be well 

 to scrutinize again the Opalinids from the latter six hosts to be sure 

 they are of this species. 



Measurements of a large individual. — ^Length of body 0.33 mm.; 

 width of body 0.068 mm. ; length of nucleus 0.0326 mm. ; width of 

 nucleus 0.01087 mm.; length of endospherule 0.003 mm.; width of 



