306 



THE MICROSCOPE. 



perfect state of development in the higher animals. Fluids 

 are collected in these vacuoles, and it is supposed they have 

 a communication, by means of some delicate vessels, with 

 the water in which the minute animal lives, so that at 

 each contraction fluids are expelled from the body, whilst 

 at each dilatation water is drawn in. When we consider 

 the very small size of these contractile organs, it is a sub- 

 ject which may well serve to excite our wonder. 



We believe, with Kiitzingand others, that the Diatomacece 

 are rightly placed by Ehrenberg among the earliest forms 

 of animal life. During an examination of the ciliary 

 motion in Desmidiacece, near the end of 

 the summer of 1854, we frequently noticed 

 in many of the more commonly-met- with 

 forms of the Diatomacece, a similar move- 

 ment of cilia. We have attentively watched 

 a diatom moving slowly across the field of 

 the microscope ; and upon meeting with an 

 obstacle to its progress, it has changed its 

 course, or pushed the obstacle aside, as if con- 

 scious of an impediment. We have again and 

 again satisfied ourselves that their motive 

 power is derived from cilia, so arranged at 

 either end, in some apparently around central 

 openings, and so completely at the will of 

 the little animals, that they are readily called 

 ^ into action as propellers, or paddles. Before 



Fig. i79.Gompho- satisfying ourselves of the presence of cilia, 

 TnTca e ua/um im we t ^ lou g nt tne motion of these little 

 creatures somewhat remarkable, steering 

 their course as they did by a power which they evi- 

 dently were able to call into action, or restrain at will ; 

 we were therefore agreeably surprised to find this motive 

 power due to cilia. The distribution of the cilia differs 

 from that observed in Desmidiacece; the ciliary motion 

 seen in which we believe to be due to physical force 

 acting independently of controlling power. On the con- 

 trary, the Diatomacecej with their cilia, may be said to act 

 in obedience to a will, for intervals of rest and motion are 

 clearly perceptible. 



From that time to the present summer we have made 



