OF MICRO-ORGANISMS. 



53 



it casts its trichocysts upon its victim from a distance. 

 The importance of this instance induces us to stop 

 here a moment. 



The Didinium (fig. 7), 

 J^v as regards the general 

 \\J shape of the body, may 

 '■ be compared to a dimin- 

 utive cask, rounded off at 

 one of the ends and term- 

 inated at the opposite ex- 

 tremity by an almost level 

 surface from the midst of 

 which rises a conical pro- 

 jection quite strongly 



Fig. J.— Didinium nasutmn, sa\s:c%e&.'a\3x\e,A.. This projection 

 two hundred diameters. The figure rep- . r j i - ■ 



resents ^Didinium overpowering a Pa- IS an Organ of deglutition 

 ramaciuni aurelia. The nettle-like fila- 1 1 • \ 



ments discharged by the Didinium are (SWalloWing) ; a longltU> 

 seen on all sides of the Paramecium; _ . . .... , , 



while the latter, already seized by the dinal StriatlOn IS notlCcd 

 tongue-shaped organ of the Didinium, is _ j r - 



being gradually drawn towards the buo- here formed of mmute 

 cal orifice (after Balbiani). 



sohd rods, of extreme ten- 

 uity and independent of the sides. These organs 

 are the weapons used by the Didinium in attacking 

 the live prey which constitutes its sole nourishment. 

 Not only does it attack and devour animalcula 

 almost as large as itsfelf, but frequently it even seizes 

 individuals of its' own kind. In such cases it is always 

 Infusoria, and never the Rotatoria, although the latter 

 often abound in waters which the Didinium inhabits. 

 It appears, moreover, to have a marked predilection 

 for certain species; and so it happens that the huge 

 and inoffensive Paramcecium au7-elia is almost always 

 its choice by preference among the animalcula that 

 inhabit the same liquid.* 



* The Didinium, Balbiani tells us, never attacks the Parmcrcium bursaria, 

 which is distinguishable from the P. aurelia by its green coloration. 



