;,i;,S si wiMAItY OF CURRENT RESEARCHES RELATING TO 



distinguished, the upper homogeneous, the lower librillated. In con- 

 nexion with the development of the air-sac in Tetrodontidae and 

 Diodontidae there is a special development of sub-cutaneous tissue, 

 (•specially ventrally, and there is an outer circular layer or muscle around 

 the body, and an internal longitudinal layer on the ventral surface. 

 The Balistidae, Diodontidse, and Tetrodontidae form a series. The 

 Molidae and Ostraciontidse are more primitive. 



C General. 



Olfactory Reactions in Amphibians.* — Jonathan Risser has made 

 many experiments with adult and larval frogs and toads. In its method 

 of obtaining food the toad seems to respond to the visual stimulus 

 entirely. This stimulus is apparently effective only when it involves 

 motion. It is not always followed by perfect reaction, for inappropriate 

 substances are often taken. Rejection of such material occurs in com- 

 pliance with mechanical or tactile stimulation. 



The gustatory function does not seem to be of any importance in 

 feeding. There is no proof that the epithelial end-plates of the mouth 

 cavity are gustatory in function. Deglutition follows almost instantly 

 on ingestion. Odours when in relation with food are not sufficiently 

 deterrent in action to compel the toad to refuse such food. At present 

 there is no evidence that odours in soil or water are effective in any 

 degree on the olfactory organ of the toad. 



In contrast with the tadpoles of the frog, the toad tadpole appears 

 to have an olfactory sense, and the nasal openings are relatively larger. 

 It is more than probable that toad tadpoles recognize certain foods and 

 their odours. Organs of taste have not been demonstrated in the mouth 

 of the tadpole. 



The Anura have receptor organs identical with those found associated 

 with the olfactory sense in the higher Vertebrates. The receptor peculiar 

 to the olfactory organ of all Vertebrates consists of a neurone whose 

 cell-body is peripheral in position. The distal portion of the neurone 

 is characterized by the protoplasmic processes projecting above the level 

 of the surrounding cells, while the proximal end is attenuated and gives 

 rise to one of the fibres of the olfactory nerve. It was formerly sup- 

 posed that such receptors responded to stimuli only when the cell 

 surfaces were dry, but the work of Aronsohn and Veress has shown that 

 in man and the higher Vertebrates the olfactory epithelium is bathed by 

 glandular secretions, and whatever stimulus reaches the receptor must 

 do so in the form of solutions. More recently, Baglioni, Parker, Sheldon 

 and Copeland have shown that the stimuli inducing certain reactions 

 in aquatic animals are identical with those noted in air-breathing 

 animals. That well-defined and characteristic motor reactions have not 

 yet been recognized in frogs and toads as results of stimuli varying in 

 quality may be due to some defect in method. 



What has been established is thus summarized. There is no evidence 

 that toads react to olfactory stimuli pertaining to soil, water, etc. The 

 character of the food is not differentiated by attendant odours to the 



* Journ. Exper. Zool., xvi. (1914) pp. 617-52 (1 fig.). 



