22 



LECTURE 11. 



The motions of the Polygastria have appeared to me, long watching 

 them for indications of volition, to be in general of the nature of 

 respiratory acts, not attempts to obtain food or avoid danger. Very 

 seldom can they be construed as voluntary, but seem rather to be 

 automatic ; governed by the influence of stimuli, within or without 

 the body, not felt, but reflected upon the contractile fibre ; and 

 therefore are motions which never tire. We may thus explain the 

 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 oflf 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 Amcebcea 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. 



The eye-speck {Jig. 11. c), as 

 the bright pink spot has been 

 interpreted by Ehrenberg, is 

 usually single, e. g. Ambli/ophis, 

 Euglena, Chlorogonium ; but is 

 double in Distigma : it is absent 

 in the Astasicece, which have 

 other close relations to the single- 

 celled plants. 



In many Polygastric animal- 

 cules, e. g. Vorticella, Loxodes, 

 there is a permanent cavity 

 {fig. 18. a.) in the interior of the 

 cell-like body, which opens ex- 

 ternally. This aperture, which 

 may be termed the mouth, is sometimes sessile, sometimes placed upon 



Monad of Volvox. 



