SENSE ORGANS. 193 



sea, the olfactory pits are particularly complex, and the 

 olfactory lobes are of enormous size, often as large or 

 even larger than the cerebrum (Fig. 124). 



Invertebrates. — That many invertebrates, especially 

 insects, have a keen sense of smell is clearly evidenced 

 by the fact of their being attracted by odors, as blow- 

 flies by putrid flesh or butterflies by the fragrance of 

 flowers. But where the organs of this sense are situated 

 is not certainly known. The reason why it is so difficult 

 to determine is that there is no instrument connected 

 with the sense by which we can know it. It is probable, 

 however, that in the case of insects it is situated in the 

 antennae. Insects are air-breathing. The breathing 

 tubes, as we shall see hereafter, penetrate every part of 

 the body, but especially pass into and to the end of all 

 branches in the antennae. In spiders, too, the organ of 

 smell, as well as of hearing, is supposed to have been 

 found in the feelers.* 



In still lower invertebrates the organs of smell have 

 not been certainly detected. 



SENSE OF TASTE AND ITS ORGAN, THE TONGUE. 



What we usually call taste is a complex sensation, a 

 mixture of several sensations. It is impossible to dis- 

 cuss the subject scientifically without analysis. There 

 is usually a mixture of three sensations belonging to as 

 many different kinds of nerves — viz., common sensation, 

 smell, and taste proper. 



Examples of mixture of gustation with common sen- 

 sation are numerous. The same batch of dough may 

 be so mixed and baked that it shall be heavy and stick 

 to the teeth in chewing, or ma}' be light and spongy. 

 The one we call disagreeable, the other agreeable, to the 



* Dahl, An. and Mag. Nat. Hist., xiv, 329, 1884. 



