648 JONATHAN RISSER 



In the series of tests there was always positive reaction in the 

 presence of the animal food when opportunity for such choice 

 was given. Organs of taste have not been demonstrated in the 

 mouth of the tadpole. 



On the other hand, the differentiation of the nasal epithelium 

 into the characteristic olfactory organs and the supporting 

 structures takes place very early and we may safely assume the 

 reactions noted to be the result of stimulation of the olfactory 

 receptors. 



3. Conclusion 



The anurans have been called microsmatic animals; such dis- 

 tinction being based on histological and anatomical comparison 

 with the animals classed as macrosmatic. 



The nasal organ of the Anura is a common respiratory and 

 olfactory organ, and in this respect conforms to the organ pos- 

 sessed by the higher vertebrates. 



A chambered nasal cavity of considerable magnitude supplied 

 extensively with olfactory epithelium and adequate connections 

 with the central nervous system, predicate functional activity of 

 the sense organ. 



The life habits and the phylogenetic position of the anurans 

 suggest that such functional activity not only be present but 

 adequately developed. The presence of receptor organs identical 

 in structure with those found in the higher vertebrates further 

 postulates that functions peculiar to these structures be identical. 



The receptor peculiar to the olfactory organ of all verte- 

 brates consists of a neurone whose cell body is peripheral in posi- 

 tion. The distal portion of the neurone is characterized by the 

 protoplasmic processes projecting above the level of the sur- 

 rounding cells, while the proximal end is attenuated and gives 

 rise to one of the fibers of the olfactory nerve. This type of 

 receptor is directly comparable structurally with neurone cells 

 found in the epidermis of many invertebrates (Parker '12). 

 Neurones such as these, found in some of the invertebrates are 

 distinct portions of the receptor-effector system and have been 

 demonstrated as extremely sensitive to chemical stimuli. That 



