242 THE AMERICAN MONTHLY [November, 



ward the throat cavity called the ^ outer end." The opposite end or 

 " inner end " is toward the dermis where the blood-vessels, connective- 

 tissue and nerves lie. The cell contains protoplasm in the centre of 

 which is a nucleus ; in the presence of these and in their chemical com- 

 position they are like cells generally or like Amceba. The outer ends 

 of these cells are furnished with a peculiar coat of" cilia." These are 

 minute hair-like bodies slightly curved and tapering. They are com- 

 posed of protoplasm and are a continuation of the protoplasm of the 

 cell body. These cilia are in living cells in constant motion, they wave 

 back and forth like the oars in a row boat, but they do not all move 

 simultaneously, some, are at any instant thrown forward and others 

 drawn back. The movement of the cilia further is a strong beat in one 

 way and a gentle recover in the opposite way, and since the thrust of 

 all the cilia is strong one way and weak the other they create a current 

 in the direction of the strong thrust. Some more facts need to be 

 noted here before we address ourselves to the task of interpreting these 

 facts in terms o1^ protoplasmic activity. The cilia are in a dai'k place, 

 yet they are constantly at work day and night. They even work for a 

 time after the heart stops beating and we say the frog is dead. Their 

 action is not dependent on any direct stimulation so far as anybody 

 knows, but they can be made to work faster or slower by application 

 of heat or cold. 



Let us now, having noted these facts, seek the interpretation of them 

 by reference to the biological principles already stated. The motion 

 of the cilia is in the first place plainly a case of the ejfercise of the 

 protoplasmic function of movement (p. 126). The cell as a whole 

 does not have power of movement like the amoeba, but retains a con- 

 stant shape and fixed outline, but the protoplasmic projection on cilia 

 contracting alternateh' on either side presents this power. This act is 

 paralleled among the low animals called infusoria, of which Vorticella 

 is a good example. Here a single cell furnished with its circle of cilia 

 around one end can bv their aid cause a current which tends constantly 

 in one direction in this case, furnishing food to the creature. But our 

 comparison of the ciliated cell with vorticella will not bear pushing too 

 far ; in Vorticella the motion of the cilia is constant so long as Vorticella 

 remains undisturbed, but directly you jar it or some little swimming 

 creature runs against it the cilia cease their action and the Vorticella 

 retracts noon its stem. It exhibits thus a certain power of reflex ac- 

 tion, and can behave in response to the circumstances which may envi- 

 ron it. The frog's ciliated cells, unlike Vorticella, have a constant cili- 

 ary motion which not even the death of the frog can immediately aflect. 

 A certain power of cell life is thus lost or virtually lost, and we may 

 sa}?^ that the cell has no power to control the ciliary motion in response 

 to external conditions. The case is something as we may imagine it 

 would be in Vorticella^, which for many generations had been in a situa- 

 tion where they never met any disturbance, hence never exercised their 

 power to contract, and finally lost the power through disuse. 



A knowledge of the ciliated cells shows another point of similarity 

 between them and elementary simple animals. The individual cells 

 have a comparatively brief existence, and yet the tissue continues and 

 ou-lasts the life of th,e frog. This is brought about by the fact that the 

 individual cells are constantly producing more cells by division, by 



