INTRODUCTION. 



XXXI 



The otocysts or simple ears of worms and molluscs are minute and usually 

 difficult to find, as is the auditory nerve leading from them to the nerve-centres. In 

 the clam it is to be looked for in the so-called foot. In the snails, as also in cuttle-fish, 

 the auditory vesicles are placed in the head close to the brain. The ears of Crustacea 

 are sacs, formed by inpushings of the integument and filled with fluid, into which hairs 

 project, and which contain grains of sand which have worked in from the outside, or 

 concretions of lime. These are situated in the shrimps and crabs at the base of the 

 inner antenna, but in a few other Crustacea, as in Mysis, they are placed at the base 

 of the lobes of the tail. In the insects the ear is a sac covered by a tympanum, with a 

 ganglionic cell within, leading by a slender nerve-fibre to a nerve-centre, and in these 

 animals the distribution of ears is very arbitrary. In the locust they are situated at the 

 base of the abdomen ; in the green grasshoppers, or katydids, and the crickets, in the 

 fore tibisB ; and it is probable that, in the buttei'flies, the antennse are organs of hearing. 

 The vertebrate ears are two in number, and occupy a distinct permanent position in 

 the skull, however much modified the middle and outer ear become. — (Packard's 

 Zoology.) 



" Throughout the animal kingdom," says Romanes, " the powers of sight and of hear- 

 ing stand in direct ratio to the powers of locomotion ; " on the other hand, in fixed or 

 parasitic animals, the organs of hearing and sight are among the first to be aborted. 



The sense of smell is obscurely indicated by special organs in the invertebrate ani- 

 mals ; nasal organs, as such, being characteristic of the skulled vertebrates. Whether 

 organs of smell exist in any worms or not is unknown ; there are certain pits in some 

 worms which may possibly be adapted for detecting odors. In some insects, at least, 

 the organs of smell are without doubt well developed ; the antennse of the burying 

 beetles are large and knob-like, and evidently adapted for the detection of carrion. It 

 is possible that certain organs situated at the base of the wings of the flies, and on the 

 caudal appendages of the cockroach and certain flies, are of use in detecting odors. 



ANIMAL PSYCHOLOGY. 



We have seen that .animals have organs of sense, of perception, in many cases 

 nearly as highly developed as in man, and that in the Mammalia the eyes, ears, organs 

 of "smell and touch differ but slightly from those of our own species ; also that the 

 brain and nervous system of the higher mammals closely approximate to those of man. 

 We know that all animals are endowed with sufficient intelligence to meet the ordinary 

 exigencies of life, and that some insects, birds, and mammals are able, on occasion, to 

 meet extraordinary emergencies in their daily lives. These facts tend to pi-ove that 

 all animals, from the lowest to the highest, possess, besides sensations, certain faculties 

 which by general consent naturalists call mental, because they seem to be of a kind, 

 however different in degree, with the mental manifestations of man. Besides in 

 many if not most highly organized animals, sensations give rise to emotions, and 

 in the higher animals, as well as man, the latter give rise to thoughts. The study 

 of mental phenomena is the science of psychology. The study of the sensations and 

 instincts, as well as reasoning powers, of animals, is called animal psychology. The 

 materials for the study of animal psychology are derived from the observations of 

 the actions of animals ; we do not, so to speak, know what is going on in their minds ; 

 we draw our conclusions, as to whether an animal thinks or reasons, by studying our 

 own mental processes. The study of human psychology is a most difficult one : one 



