16 
Balantidium blattarum n. sp. 
Scheier (Arb. d. St Petersburger naturf. Gesellsch. xxvm. No. 4) defines the 
two genera in the following manner: Balantidium: body egg-shaped or 
cylindrical; contractile vacuoles numerous; macronucleus oval or horseshoe- 
shaped. Balantidiopsis: body broadly oval; contractile vacuole single, 
posterior; macronucleus spherical. 
This year I described two new species of Balantidium and Balantidiojpsis 
(Bull. Carmichael Med. College, No. 2) to which I appended synopses of the 
known species of both the genera. But the recognition of a large number of 
species of both the genera has made all the distinguishing characters fail one 
after another, viz. the number of contractile vacuoles, the form of the macro¬ 
nucleus and the nature of the habitat. Lastly, the discovery of species with 
oval transverse section of the body breaks the last distinction between the 
two genera. Under these circumstances it seems necessary to reunite the two 
genera into Balantidium, as already suggested by Bezzenberger (Arch. f. 
Protistenk. m. 154-156). 
As regards habitat, the already known species of Balantidium have been 
found in the gastric cavity of Hydra (B. hydrae, Entz, Arch.f. Protistenk. 1912, 
xxvii.) and medusa, and in the intestinal canal of the mollusc and of many 
vertebrates, specially the amphibians. The present species seems to be the 
first described from the intestinal tract of an arthropod. 
