170 ON THE EXTERNAL SENSES 



the shrew and mole; in the latter of which the eye is not larger than a 

 pin's head. 



The iris, with but few exceptions, partakes of the colour of the hair, and is 

 hence perpetually varying 1 in-different species of the same genus. The pupil 

 exhibits a very considerable, though not an equal, variety in its shape. In 

 man it is circular; in the lion, tiger, and indeed all the cat-kind, it is oblong; 

 transverse in the horse and in ruminating animals; and heart-shaped in the 

 dolphin. 



In man, and the monkey tribes, the eyes are placed directly under the fore- 

 head ; in other mammals, birds, and reptiles, more or less laterally ; in some 

 fishes, as the genus pleuronectes, including the turbot and flounder tribes, 

 both eyes are placed on the same side of the head ; in the snail they are 

 situated on its horns, if the black points on the extremities 'of the horns of 

 this worm be real eyes, of which, however, there is some doubt ; in spiders 

 the eyes are distributed over different parts of the body, and in different 

 arrangements, usually eight in number, and never less than six. The eyes 

 of the sepia have lately been detected by M. Cuvier : their construction is 

 very beautiful, and nearly as complicated as that of vertebrated animals.* 

 Polypes and several other zoophytes appear sensible of the presence of light, 

 and yet have no eyes ; as the nostrils are not in every animal necessary to 

 the sense of smell, the tongue to that of taste, or the ears to that of sound. 

 A distinct organ is not always requisite for a distinct sense. In man himself 

 we have already seen this in regard to the sense of touch,, which exists both 

 locally and generally : the distinct organ of touch is the tips of the tongue 

 and of the fingers, but the feeling is also diffused, though in s subordinate and 

 less precise degree, over every part of the body. It is possible, therefore, 

 in animals that appear endowed with particular senses, without particular 

 organs for their residence, that these senses are diffused, like that of touch, 

 over the surface generally ; though there can be no doubt that, for want of 

 such appropriate organs, they must be less acute and precise than in animals 

 that possess them.f 



But who of us can say what is possible 1 who of us can say what has 

 actually been done ? After all the assiduity with which this attractive science 

 has been studied, from the time of Aristotle to that of Lucretius, or of Pliny, 

 and from these periods to the present day, after all the wonderful and im 

 portant discoveries which have been developed in it, natural history is even 

 yet but little more than in its infancy, and zoonomy is scarcely entitled to the 

 name of a science in any sense. New varieties and species, and even kinds 

 of beings, are still arising to our view among animals, among vegetables, 

 among minerals : new structures are detecting in those already known, and 

 new laws in the application of their respective powers. ' 



But the globe has been upturned from its foundation ; and with the wreck 

 of a great part of its substance has intermingled the wreck of a great part 

 of its inhabitants. It is a most extraordinary fact, that of the five or six 

 distinct layers or strata of which the solid crust of the earth is found to con- 

 sist, so far as it has ever been dug into, the lowermost, or granitic, as we ob- 

 served on a former occasion,! contains not a particle of animal or vegetable 

 materials of any kind ; the second, or transition formation, as Werner has 

 denominated it, is filled, indeed, with fossil relics of animals, but of animals 

 not one of which is to be traced in a living state in the present day ; and it is 

 not till we ascend to the third, or floetz stratification, that we meet with a 

 single organic remain of known animal structures. 



M. Cuvier has been engaged for the last fifteen years in forming a classifi- 

 cation, and establishing a museum of non-descript animal fossils, for the 

 purpose of deciding, as far as may be, the general nature and proportion of . 

 those tribes that are now lost to the world : and in the department of quad- 

 rupeds alone, his collection of unknown species amounted in the year 1810 to 

 not less than seventy-eight, some of which he has been obliged to arrange 



* Le Rgne Animale distribue d'apres son Organization, 4 tomes, 8vo. Paris, 1817. 



t Study of Med. vol. iv. p. 14, 2d edit. 1825. t Series i. Lecture vi p. 69 



