634 



CILIA. 



Ciliograde Medusae afford a good example. In 

 these, in place of cilia of the usual form and 

 arrangement, there are rows of broad flattened 

 organs, each of which is made up of several 

 simple filaments joined together by a common 

 base, according to Eschscholz, or according to 

 Dr. Grant by a connecting membrane in their 

 whole length. The entire organ is raised or 

 depressed at once, so that the filaments are all 

 moved simultaneously, like the eye-lashes. The 

 compound cilia in some of the Rotatoria, de- 

 scribed by Ehrenberg, are probably of the same 

 nature. 



5. Of the appearance of the cilia in motion. 

 On examining these organs with a lens of 

 ^ inch focus, when their motion is not very 

 rapid, the manner in which the individual cilia 

 move may be distinguished with tolerable cer- 

 tainty. Most commonly they have a fanning 

 or lashing motion, that is, the cilium is bent in 

 one direction and returns again to its original 

 state. The flexion takes place chiefly at the 

 base or root, but not wholly there, for the 

 rest of the organ is obviously bent and altered 

 in figure ; nay, the more elastic cilia, when 

 their motion abates in intensity, appear some- 

 times to bend only near the point, the base 

 and adjoining part remaining motionless. 



When a number of cilia are affected in suc- 

 cession with this motion, the appearance of a 

 progressive wave is produced, and as in such a 

 case they are again and again moved in the 

 same way at very short intervals, successive 

 waves proceed along them in the same direc- 

 tion, which might be compared to those pro- 

 duced by the wind in a corn-field. Such at 

 least seems to be the true explanation of the 

 undulatory motion which so often occurs, 

 although it must be confessed that the motion 

 of the cilia individually cannot be distinctly 

 seen when the undulation is most perfect. The 

 undulations succeed one another along a range 

 of cilia with great regularity, and except in 

 the Rotifera, and perhaps some other Infusoria, 

 they seem always to maintain the same direc- 

 tion in the same parts. 



Purkinje and Valentin describe the motion 

 of the individual cilia as being more frequently 

 rotatory, or, as they term it, infundibuliform ; 

 and Ehrenberg states this to be the common 

 mode in the Infusoria ; the cilium describing a 

 circle with its point, while the base is the centre 

 of motion. From my own observation, how- 

 ever, I would be inclined to infer that this 

 motion is by no means the most common. 



6. Duration of the ciliary motion after death 

 and in separated parts. The continuance of 

 the ciliary motion for some time after death, 

 and the perfect regularity with which it goes on 

 in parts separated from the rest of the body, are 

 facts which have been already repeatedly .stated, 

 and sufficiently prove that the motion is quite 

 independent of the will of the animal, and also 

 that it is not immediately influenced by the 

 circulation of the blood, even in the respiratory 

 organs. 



The time which it continues after death 

 differs in different species of animals, and also, 

 but in a much smaller degree, in different parts 



of the same animal. Its duration is influenced 

 also by the temperature of the air, and by the 

 nature of the fluid in contact with the surface. 

 In Mammalia and Birds the period varies from 

 half an hour to four hours, being longer in 

 summer than in winter; but it is still further 

 prolonged when the parts are covered with 

 blood. In the gills of Batrachian larvae I have 

 seen the motion continue six hours; but of all 

 vertebrated animals it is most enduring in the 

 Tortoise, in which animal Purkinje and Valen- 

 tin affirm they observed it fifteen days after 

 death, when putrefaction was far advanced ; 

 the irritability of the muscles remained in the 

 same animal for seven days. Among the in- 

 vertebrata the River-mussel affords an instance 

 of the great pertinacity of the motion, which 

 ceases only when putrefaction has advanced so 

 far as actually to destroy and dissolve the 

 tissues. 



7. Effects of external agents on the ciliary 

 motion. Steinbuch, Purkinje, and Valentin 

 allege that on touching the parts, or giving 

 them a gentle shock by merely striking against 

 the object plate of the microscope, the motion 

 is rendered brisker when it has become languid, 

 or is even renewed in parts where it has ceased. 

 They, however, attribute more importance to 

 this fact than it seems to deserve ; for it may be 

 doubted whether the concussion in renewing 

 the vivacity of the cilia does not act merely by 

 removing obstacles which impede their play. 



Electricity and galvanism produce no visible 

 effect. A powerful discharge from a Leyden 

 jar was made to pass through the River-mussel 

 by Purkinje and Valentin without causing any 

 change in the ciliary motion. Portions of the 

 external gills of the Tadpole were subjected by 

 myself to the same experiment and with a 

 similar result, except when the surface was 

 abraded, which occasionally happened with a 

 strong discharge. I have exposed portions of 

 the gill of the River-mussel while viewed with 

 the microscope, to the influence of a galvanic 

 battery of twenty-five pairs of three-inch square 

 plates, charged with solution of salt, without 

 being able to perceive the slightest effect on the 

 motion of the cilia. The authors above men- 

 tioned obtained a similar result, both in the 

 Mussel and the domestic Fowl. 



The effect of temperature is different in warm 

 and cold-blooded animals. In the former, ac- 

 cording to Purkinje and Valentin, the motion 

 stopped on exposure to a temperature of 43 F. 

 while it went on at 54 F. On the other hand 

 they found that in the Fresh-water Mussel it was 

 not affected at 32 F. ; and I found the same 

 to be true of the Tadpole. A portion of the 

 gills of the River-mussel, which I kept for five 

 minutes in water at 96 F. shewed no change. 



Acids, saline solutions, and other substances 

 applied to the parts, differ in their effects ac- 

 cording to the kind of animals submitted to 

 experiment. Thus, for example, fresh water 

 instantly arrests the motion in the Marine Mol- 

 lusca, and also in other marine animals in 

 which I have tried its effect, though a satu- 

 rated solution of sea-salt destroys it both in 

 salt and fresh-water species. Purkinje and 



