334 DESIGN IN NATURE 



force, and it takes an effort to realise the amazing potentialities of both. At the very threshold of animal existence, 

 so to speak, we are confronted with tiny microscopic beings which are, in the ordinary sense, structureless, but 

 which nevertheless are endowed with powers and properties which enable them to live amongst matter, to select, 

 assimilate, and incorporate certain portions of it, and to reject other portions ; to employ or set aside the forces 

 inhering in the matter ; to feed, secrete, and excrete ; to respire ; to perform the function of reproduction ; and 

 to move voluntarily in all their parts and particles to given ends, as happens in the higher animals. No nervous 

 system can be traced in the amoeba. It, however, possesses a nervous system potentially. 



The movements of the amoeba cannot be too carefully studied. In them, it appears to me, are to be found the 

 types, models, and principles of organic movement as a whole. They wonderfully resemble, as already indicated, 

 the movements of the sarcous elements of muscles, on which not only locomotion, but ahmentation, respiration, 

 circulation, urination, defsecation, and parturition in the higher animals depend. 



If an adult healthy amoeba be examined by the aid of the microscope in a good light it will be seen to move 

 wholly or in part. The manner of its movement is pecuHar. Its substance flows out in wedge-shaped portions in 

 an aggressive, centrifugal manner. It invades territory, and it envelops food by throwing itself upon or over 

 it. In the advancing, aggressive movement there is no trace of constriction or contraction of any Idnd in the 

 substance or body of the amoeba. The parts thus advanced are, as a rule, numerous ; the animal as it were 

 streaming from a central point by means of blunt pseudopods in skirmishing order. When one or more pseudopods 

 encounter a food particle they, with the captured food particle, are withdrawn into the substance and central mass 

 of the animal by retreating, centripetal movements which are the converse of the original aggressive, centrifugal 

 movements. As in the centrifugal movements there was no trace anywhere of constriction or contraction, so 

 in the centripetal movements there is no trace of elasticity. The centripetal and centrifugal movements are 

 spontaneous, rhythmic, vital movements, and are not dependent on either contraction or elasticity ; neither are 

 they due to irritability or stimulation of any kind. They are voluntary flow-and-ebb movements, and have equal 

 values. Their function is obvious. They are for the purpose of securing food. When the protoplasm of the 

 amceba flows as a mass and as a whole in a particular direction, the animal progresses and changes locality. In 

 the movements of the amcBba there is no increase or diminution of bulk ; the sarcode advancing or retiring in 

 wave-fashion, in good order, and deliberately. The amoeba may arrange its substance by an elongating movement 

 of its protoplasm, say from right to left at one time, and at another at right angles by a counter movement, in which 

 case the phenomena witnessed in the sarcous elements of muscles during relaxation and contraction are accurately 

 reproduced. In relaxing and contracting muscles the long axes of their sarcous elements are always arranged at 

 right angles to each other. 



§ 6i. Paramecium caudatum. 



The Paramecium is a minute, comparatively simple organism which inhabits fresh water and can be seen with 

 the naked eye. It is a type of the sub-kingdom Protozoa, being composed of a single cell with all its activities 

 confined thereto ; it is a representative of the Corticata, as it is limited by a cortex and has a definite shape ; it 

 belongs to the class Ciliata, cilia forming its means of propulsion. 



I append a figure of it (Fig. 69) as enlarged 60 diameters. 



The Paramecium is an advance on the amoeba, having a definite shape, a hmiting cortex, a mouth, an imperfect 

 anus, ciha for propulsion and securing food, and the power of causing the food to gyrate within its substance in a 

 given direction. It reproduces itself by a double process of fission and conjugation, whereby two separate individuals 

 complete the reproductive act. 



The body of the paramecium is soft, flexible, cylindrical and oval-shaped, with a dorsal and ventral surface. It 

 consists essentially of two parts : (a) an internal semi-fluid protoplasm in which are found a double nucleus, two con- 

 tractile vacuoles, food-vacuoles and food particles, and, at the periphery, a number of trichocysts with stings ; and 

 (b) an external hardened layer of protoplasm designated the cortex, which is covered with a thin hyaline cuticle. In 

 the cortex are found a mouth, an imperfect anus, and numerous apertures, through which protrude a large number 

 of delicate hair-like processes (ciha) and the stings from the trichocysts. The hair-like processes or cilia, which are 

 scattered all over the body and are freely movable, serve at once for propulsion and for securing food ; those near 

 the mouth producing artificial water currents in particular directions for the latter purpose. 



The possession of ciha constitutes an important departure in the locomotion of the animal, as these hair-hke 

 processes are all under control, and can be made to move in rhythmic waves in any direction required, either for the 

 production of food currents or for propulsion. The ciha perform a double function, that is, they can either propel 

 the body as a whole, or simply produce water-currents to collect and bear food to the oral aperture. The ciliary 



