274 Dynamic Theory. 



From the first existence of the simplest organism it is liable to be as- 

 sailed by those forces to the action of which we are to trace the differ- 

 entiation of the functions of sense and their organs. Among the first 

 of these are contact, or touch, and molecular heat, or body warmth. 

 Contact being the most aggressive and forcible form of stimulus, it de- 

 velops the first organs of sense that show themselves in the simple an- 

 imal. The sense of touch is first distributed, in a greater or less degree, 

 to the whole skin or ectoderm of the animal, since it is all more or less 

 exposed to the stimulus of external contact. The infusoria continually 

 batter themselves against the sides of their environment, and against 

 each other, by the stimulation of which process, first, an ectosarc is dif- 

 ferentiated on the outside of their protoplasm, and, second, vibratile 

 cilia become set off from that. Next, the vibratile cilia especially, and 

 the ectosarc generally, may be presumed to be rendered more and more 

 sensitive through the molecular excitement. This appears to produce 

 results in the order Flagellata, which are possessed of one or two 

 flagella or long bristles. When we ascend to the Hydra, or fresh water 

 Polyp, the sensitiveness of the tentacles ( into which the cilia may be 

 said to have now grown ) is well pronounced. They draw in at the first 

 alarm. Smell and taste must be regarded as subdivisions of the tactile 

 sense. They are chemical sensations made by the contact of finely 

 comminuted particles on a part of the mucous epithelium, or invagin- 

 ated ectoderm. These senses are both of comparatively late origin. 

 But in the lower vertebrates the olfactory ganglia are relatively very 

 large. The sense is also extremely delicate in most of the mammals 

 and in the birds. In the mammals, however, the relative importance 

 of the olfactory lobes decreases as the hemispheres and the optic lobes 

 gain greater importance. 



Taste, also developed in connection with touch, is still later than smell. 

 Among the birds there is little or none of it, and many genera of mam- 

 mals possess but a faint development of it, while it is not known that 

 the sense is developed at all among the invertebrates. Yet the intimacy 

 existing between taste and smell is such that it is difficult to say with 

 certainty where one ends and the other begins, and it is safe to affirm 

 that one may make up for the partial deficiency of the other. ( We 

 will have to revert to these -matters further on. ) 



From the experiments and observations cited in former chapters, we 

 are at liberty to conclude that such Protozoa as Monera, Amoebae, &c. , 

 consist merely of a union of two vegetable elements or principles. One 

 is the active protoplasm of the plant liberated from the plant cell, and the 

 other is the co-operative fungus or diastase which in the plant appears 

 to be inseparable from the protoplasm, and which is equally necessary 

 to assist in the digestion of starchy food in the animal. The protoplasm 



