CHAPTER XVI 



Nonphotic receptors in lower forms 



H A N S J O C H E M A U T R U M | Department oj ^oology, University of Miinchen, Germany 



C: H A P T E R CONTENTS 



Protozoa : Differentiation of Protoplasmic Irritability 

 Coelenterates : Cnidoblasts as Independent Effectors 

 Higher Invertebrates: Emergence of True Receptors 

 Anatomical Peculiarities 

 Comparison of ttie Senses of the Invertebrates with Those of 



Vertebrates 

 Reactions of Simple Receptors 

 Specific Types of Receptors 

 Chemoceptors 

 Proprioceptors 

 Thermoreceptors 

 Mechanoreceptors : tactile sense 

 Mechanoreceptors : vibration sense 

 Mechanoreceptors : hearing 

 Statocysts 



protozoa: differentiation of 

 protoplasmic irritability 



PROTOZOA REACT TO STIMULI: heat, cold, chemical and 

 mechanical irritation, gravity, and light influence 

 their behavior. These stimuli therefore affect the pro- 

 tozoan cells. However, it is a significant morphologi- 

 cal and physiological problem whether sensitivity to 

 these stimuli is limited to certain parts of the proto- 

 zoan cell, or whether the whole organism can be 

 stimulated. Only if the former is true can we speak of 

 receptors. 



The bodv protoplasm and its surface is not much 

 differentiated in the simpler protozoa, such as the 

 amebae. There is therefore no reason to look for 

 localized receptors. It appears, however, that the 

 protoplasm of the ameba is not irritable under certain 

 physiological conditions. The ameba does not react if 

 a narrow light beam strikes the hyalin tip of the outer 

 end of a pseudopodium (80, 82, 83). If the light beam 



strikes the endoplasm of a p.seudopodium which is 

 streaming toward the tip (and is in the sol state), the 

 streaming of this pseudopodium is stopped and new 

 pseudopodia are formed in other parts. If the light 

 beam strikes the plasmasol some distance from the 

 tip, streaming will be accelerated. Experiments with 

 ciliates, such as Paramecium, al.so showed the suscepti- 

 bility of the whole body to stimulation (61, 71, 72). 

 Thus, separated pieces of cut Paramecium respond to 

 chemical stimuli, e.g. by 0.5 to i.o per cent NaCl or 

 0.05 to 0.0 1 per cent H-iSOj, and to temperature 

 stimuli in the same way as do whole animals. There 

 is also no difference between cut parts and whole 

 animals in the response to gravity. This fact is of 

 special interest since the sensitivity to gravity depends 

 on the principle of the statocyst (68, 69): hea\ier sub- 

 stances included in the body exert a pressure on the 

 underlying protoplasm.' However, there are no fa- 

 vored locations in the body of Paramecium sensitive to 

 this pressure; it can be effective in every part and 

 may produce orientation in relation to the gravita- 

 tional field. 



In contrast to Paramecium, only the anterior part of 

 the ciliate Sptrostomum ambiguum (which can grow to 

 4.5 mm in length) is sensitive to thermal and chemical 

 stimuli according to the view of Alverdes (6) and 

 Blattner (18). Excised posterior parts swim into dilute 

 picric acid without reaction (18). However, very di- 

 lute picric acid attracts Spirosiomum and is less toxic to 

 it than to other ciliates such as Paramecium and 

 Stentor. Therefore the findings of Blattner cannot be 



' It is not known which inclusion bodies serve as statoliths 

 causing excitation by the pressure they exert under normal 

 conditions. Koehler assumes that all inclusion bodies may func- 

 tion as statoliths. They have to be only heavier than the cyto- 

 plasm (as for example the nucleus, the content of vacuoles and 

 iron particles in experiments). 



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