OF MICRO-ORGANISMS. 29 



It is impossible to believe that these organs are 

 not eyes, for they have the same structure as the eyes 

 of comparatively higher classes of animals, such as 

 certain worms, turbellaria, rotifers, lower-class crusta- 

 ceans, etc; all these organs are similarly formed of a 

 small crystalline globule enclosed in a small mass of 

 pigmentary matter. The identity of structure natur- 

 ally leads to the assumption of the identity of 

 functions. 



The eye of the Euglena is the simplest of all; it 

 is even reduced to the maximum point of simplicity, 

 as it is composed of a spot of pigment. What induces 

 us to believe that this spot is a visual organ, is the 

 presence of this pigment. In fact this pigment is 

 found in the most elementary visual organs. A second 

 argument might be advanced; the red pigment of the 

 Euglena exhibits the same re-actions as the coloring 

 matter that fills the rods of the retina in the Verte- 

 brates. From among these re-actions common to 

 both, we cite the decoloration under the influence of 

 light (Capranica). 



Whatever the case may be, one thing is certain, 

 namely that the Euglena is very sensitive to the 

 light. When they are kept in a vessel, they are in- 

 variably seen to cover the side exposed to the light. 

 M. Engelmann has observed that light acts very 

 strongly upon this small animal; it does not act 

 directly on the spot of pigment, nor, as was formerly 

 thought, on the flagellum, but on the protoplasm which 

 is located in front of the spot. The special micro- 

 spectral object-glass that M. Engelmann constructed, 

 enables us to see that the Euglens always congregate 

 in the band F to G of the spectrum. 



So far as the vegetable Micro-organisms are con- 



