OOMPABATIVE ANATOMY. 





greater rosiHtauoo than if it acted alone. The water than im- 



piiitfuik' "" tlio central rod will be prevented from readily uniting 



!.' thor two; BO that the vacuum will be filled up, not 



wutor which has passed through the intorstiocH 



rods, but by fresh water which flows in from behind. In 



oilier wonls, win a the cflium acts alone, the resistance it meets 



with i < in proportion to the section of the rod itself; bat when 



it acts with iU neighbours, the resistance is little short of being 



: ionul, not to the section of the several rods, but to them 



and tlio whole space which lies between them. This speculation 



seems to bo confirmed by experiment ; for if a sheet of wire 



untouched the problem of how the cilia themselves an set in 

 motion. The cilia of the Hotatoria Mem to differ from tho*> 

 of most other animals in being under the control of the will of 

 the tHiim*! 



When a better appreciation of the action of the cfliary fringe* 

 of these animals was attained, the name Rotifer* ( VPtat-OMrbip 

 animalcules) was changed into Kotatoria, or rotary 

 Under this name they have been <rr ftm i r L H. and other 

 of their structure show them to be much more highly organised 

 than the simple Protozoa, which inhabit the same waters, feed 

 upon similar food, and are moved by a like agency. The * 



I. SCOLOPENDRA MonSITANS. II. GLOMEBJ8. III. JULUS. IV. ANTENNA AHD EYES OF JuLOT. V. UVDEK SlDS OF A DOUBLE 8EOXXBY OT 

 JULUS, SHOWING THE LEGS ON ONE SIDE. VI. NOTOMATA CENTBURA. VII. SCHEME 8HOWISO THE NATURE OP THE BOTAKY Tr-HHIlOST. 



Kefs, to Nos. in Figs. V. 1, spiracle. VI. 1, ciliated disc ; 2, gizzard ; 3, stomach ; 4, water- vascular system ; 5, ovum ; 6, forceps. 



gauze be passed rapidly enough through the water, it is resisted 

 with almost as great force as if it were not perforated. When 

 fine sand is thrown ont of a balloon in rapid descent, it appears 

 to fly violently upward, although the resistance opposed by the 

 atmosphere to each particle in relation to its weight is small 

 as compared to that offered by the balloon in proportion to its 

 weight. According 1 to this theory, then, a number of cilia are 

 depressed in concert and so create a wave, and only rise slowly 

 and separately after the wave has passed on, and so assume 

 an erect posture ready to propel a fresh wave at a considerable 

 distance from the one which preceded it. This conforms well 

 to the appearance created by the cilia both when they are used 

 to pass liquid over their surface, and when they are employed 

 as locomotive organs. This partial explanation leaves entirely 



have a definite alimentary canal, complete from end to end, and ir> 

 some this canal is of very complex structure. The animals arc 

 transparent, and admit of the examination of their internal 

 organs while alive ; and to aid in this examination, Ehrenberg 

 placed some indigo, in an extremely fine state of division, into 

 the water where they were. He had the satisfaction of seeing 

 the little opaque particles moved by the ciliary currents, , 

 swallowed, and pass through the whole length of the alimen- 

 tary canal, and thus make it more distinct. Immediately below 

 the gullet, in some (as in the Notomata of our illustration), to 

 an enlarged chamber, furnished with a tooth apparatus, which 

 from its internal position is called a gizzard. In the Notomata 

 the dental apparatus consists of two teeth, one situated on each 

 side of a central fixed tooth, and playing upon it aa the himMr 



