1 16 ORGANIZATION OF THE INFUSORIA. 



on the more remote objects in the microscopic field, while it may be cut 

 with the scissors to any required size or shape. 



In the investigation of the Flagellata, or indeed of any Infusoria in 

 which it is sought to arrive at an accurate knowledge of the life or develop- 

 mental history of any given type, it is desirable that the same individual 

 zooid or animalcule should be continuously examined. An important 

 mechanical obstacle that has to be overcome in the conduct of such con- 

 tinuous investigation, which may extend over many hours or days, results 

 from the rapid evaporation of the water or other fluid from beneath the 

 covering glass, combined with the necessity of keeping it constantly 

 replenished. Various mechanical appliances for accomplishing the desired 

 end have been introduced by Recklinghausen, Leuckart, and other Con- 

 tinental workers, none of these, however, being equal in efficiency to that 

 employed by Messrs. Dallinger and Drysdale, during their famous 

 " Researches into the Life-history of the Monads," figured and described in 

 the 'Monthly Microscopical Journal' for March 1874. The illustrations 

 given of this apparatus with accompanying explanations are reproduced 

 in the plate devoted to mechanical appliances at the end of the atlas to 

 this volume, and may be thus briefly described. It consists firstly of 

 a plain glass stage, about the one-tenth of an inch thick, fitted so as to 

 slide on in place of the ordinary sliding stage of the microscope. From 

 the left-hand anterior border of this stage a projecting arm is produced 

 which carries a socket for the reception of a small glass reservoir about 

 1 1 or 2 inches deep. The glass stage being too thick to work through with 

 an achromatic condenser and high powers, a circular aperture of sufficient 

 size is cut through it, and a piece of thin glass cemented on its upper 

 surface. A piece of blotting-paper is now cut coinciding in form with the 

 glass stage, but slightly smaller, and with a tongue-like projection that lies 

 along the projecting arm and dips down into the glass reservoir. A 

 circular aperture of larger size than the covering glass employed is cut 

 out of the centre of this paper, such aperture, where a ^-inch cover is 

 made use of, being preferentially the \\ of an inch. The foundation of the 

 moist chamber is now complete, and it only remains to provide the 

 bounding walls. This Messrs. Dallinger and Drysdale accomplish by 

 means of a piece of glass tubing, about i^ inch in diameter, cut to | inch 

 in length. Across one end of this tubing a thin sheet of caoutchouc is 

 next firmly stretched and securely tied, and a small hole perforated in its 

 centre. The tubing with its free edge, which should be carefully ground, is 

 now placed concentrically upon the glass stage, over the aperture in the 

 blotting-paper, and the object-glass racked down upon the perforation in 

 the caoutchouc. The caoutchouc should be sufficiently thin to offer no 

 impediment to the action of the fine adjustment, while it at the same time 

 clasps the object-glass firmly round its central perforation and in combination 

 with the lowermost or free edge resting on the blotting-paper, constitutes a 

 practically air-tight chamber. Everything is now in working action and it 



