20 



LECTURE II. 



fact which Ehrenberg relates — not without an expression of surprise 

 — namely, that at whatever period of the night he examined the 

 living Infusoria he invariably found them moving as actively as 

 in the day-time ; in short, to him it seemed that these little beings 

 never slept. Nor did this appear to be merely the result of the 

 stimulus of the light required to render them and their movements 

 visible ; since when they were observed upon the sudden application 

 of light without any other cause of disturbance, they were detected 

 coursing along at their ordinary speed, and not starting off from a 

 quiescent or sleeping state. 



Evidence of muscular action in the Polygastria is afforded by the 

 contraction and change of form of the entire body. These changes 

 are so rapid, extensive and various in certain species that it is impos- 

 sible to refer their bodies to any definite shape : such form the genus 

 Proteus of Miiller, and the family AmcebcBci of Ehrenberg. No defi- 

 nite arrangement of nervous matter has yet been detected in the 

 Polygastric Infusoria ; but its presence is indicated by the coloured 

 eye-speck in certain genera: and nervous conductors of impressions 

 are no less requisite for reflex than for voluntary motions. 



Every Polygastric animalcule, like every other true animal, has 

 a distinct mouth, which is sometimes placed upon a long extensile 

 neck, as in Lachrymaria ; in many of the monads it is provided with 

 a long tentacle or a pair of tentacles (y?^. 9. a.) ; in other species it is 



armed with a curious dental ap- 

 paratus, consisting of a series of 

 long, slender and sharp teeth, ar- 

 ranged side by side, in the form 

 of a cylinder, as in Chilodon and 

 Nassula {Jig. 11. «, a). 



If you remove some of these 

 animalcules from their native in- 

 fusion to a drop of clear water, 

 and, after they have fasted a few 

 hours, add a drop of the solution 

 of pure indigo or carmine, the 

 fine particles of these colours will 

 be greedily swallowed, and will 

 soon be seen to fill successively a 

 number of pyriform or spherical 

 cavities {fig. 5. b.) in the interior 

 of the animal. In some species these assimilative cells exceed 100 in 

 number, and if, with Ehrenberg, we call them stomachs, they afford 

 a very interesting example, in these early forms of animal life, of the 

 irrelative repetition of this most essential and characteristic organ of 



Monad of Volvox. 



