£04 NOTES ON SOME CANADIAN INFUSORIA. 



the form which I observed differ so very considerably from those of 

 M. sigmoides, that I think it necessary to regard it, however, as a 

 new species. M. sigmoid es is described by Claparede and Lachmann 

 as having the buccal fossa bounded by cilia much more vigoi-ous than 

 those of the rest of the body. In the digestive cavity anteriorly are 

 constantly found a number of granules, highly refractive, whose 

 signification is still problematic, and which recall very strongly those 

 found frequently in Paramecium Aurelia, and in certain Nassulm. 

 The contractile vesicle is spacious, and lodged in the posterior half of 

 the body, which is S-shaped. In the figure they represent the 

 nucleus as a morula-like structure. Engelmann 1 describes it thus : 

 "It reaches a size of only 0.15 mm., posteriorly is bent towards the 

 right not quite S-shaped, possesses at the posterior extremity some 

 long bristles and at the centre of the body a usually curved reniform 

 nucleus. Metopus possesses an adoral row of cilia of short bristles, 

 which are however in a strange manner fastened not on the upper 

 but on the lower side of the long peristome field. The upper border 

 of the peristome bears the usual cilia, as well as the whole anterior 

 half of the body." Engelmann's form accordingly differs from that 

 of Claparede and Lachmann in the possession of terminal setse, 

 which are neither mentioned by the latter authors in the text, nor 

 represented in their figure ; also in the absence of the highly refrac- 

 tive bodies, and in the shape and appearance of the nucleus. Stein, 

 again, describes this same form as occurring in three distinct shapes — 

 the normal, described above, the shortened, and the rolled up ; and 

 also describes a bunch of terminal setse and a terminal anus. He 

 criticises Claparede and Lachmann's figure somewhat harshly, point- 

 ing out the non-pourtrayal of the proper curvature of the posterior 

 portion of the body, and the incorrectness of the structure of the 

 peristome and the nucleus, and the absence of the terminal bristles. 

 He evidently does not recognize the possibility of the form observed 

 by the Swiss authors being different from that he describes. 



The form. I observed differs from these descriptions in many 

 respects, and the various differences may be discussed serially. 



(1) The twisting does not appear to be as extensive as described 

 for M. sigmoides. On examining the figures of C. and L. it appears 

 that the plane of the anterior half of the body is parallel with that 



1 Zeit. fiir Wiss. Zool. XI. 1361. 



