OF MICRO-ORGANISMS. 



ii 



compared, but that it is completely under the control 

 of the will of the animal, like the organs of locomotion 

 of animals much higher in point of organization. 



" The Didinium has two rows of equal, and rather 

 strong, vibratile cilia, disposed transversely around 

 the body, in the form of two belts or crowns. The 

 rest of the body of this animal is entirely stripped of 

 cilia, but its double vibratory belt suffices to enable it 

 to execute the most rapid and most varied evolutions 

 in the water. Not only does it swim forwards and 

 backwards with perfect ease, but the progression in 

 both directions is always accompanied by a rapid rota- 

 tory movement of the animal about its longitudinal axis, 

 similar to that observed in other infusoria that have a 

 cylindrical body. The two rows of cilia always act in 

 union during the locomotion, and the direction which 

 the animal gives to them, determines the direction in 

 which it wishes to move. In the movement for- 



Fig. i. Didinium na- 

 sutum (Balbiani) Fig- 

 ure representing move- 

 ment forward. The cilia 

 are all turned towards 

 the front part of the 

 body. 



Fig. 2. Didinium na- 

 sututii (Balbiani). Out- 

 line of movement back- 

 wards. The cilia are 

 all turned towards the 

 back part of the body. 



Fig. 3. Didinium na- 

 sutum (Balbiani). A 

 sketch of rotatory 

 movement in one spot. 

 The cilia of the ante- 

 rior belt are directed 

 forwards, while those 

 of the posterior belt 

 are directed backwards 



wards, all the cilia are directed toward the an- 

 terior part of the body (fig. i); when it swims 

 backwards, they are reversed (fig. 2). The in- 

 fusory thus rapidly makes its way across the field of 

 vision by jerks; from time to time it suddenly stops, 

 all the time continuing to turn around rapidly on its 



