60 EVENINGS AT THE MICEOSCOl'E. 



either beneath the margin of the solid shell, or, if pro- 

 jected, projected only in the smallest degree, and en- 

 dowed with the power of retreating beneath its barrier 

 with the rapidity of thought on the least alarm. 



• There can be no donbt that these points, numerous 

 as they are, are true eyes, endowed with the faculty of 

 vision in a well-developed degree. For when their 

 structure is carefully examined by the skilful anatomist, 

 each is found to be covered with the proper sclerotic 

 tunic which becomes a perfectly transparent cornea in 

 front, and to possess a coloured iris, — perforated with 

 a well-defined pupil, and connected with a layer of pig- 

 ment which lines the sclerotic tunic, — a crvstalline lens, 

 and a vitreous humour for the due refraction of the 

 i"ays of light, and a retina in their focus, formed by an 

 expansion of the optic nerA^e, and fitted to receive the 

 picture ; the sensation of which is then conveyed by an 

 optic nerve from each eye to the common nerve-trunk, 

 which runs along the border of the mantle. Thus there 

 exists in each of these lustrous points every element 

 needful for the due performance of vision, though, prob- 

 ably, the impressions thus conveyed may be neither so 

 powerful, nor so distinct as those which are conveyed 

 by the eyes of vertebrate animals. They are, how- 

 ever, we may be sure, amply sufficient for the M^ants of 

 the pretty Scallop, and are fresh proofs of the Divine 

 wisdom and benevolence. 



We haA^e been accustomed, from childhood, to recog- 

 nise as eyes the shining black extremities of the upper 

 pair of " horns " in the Garden Snail. And though 

 some naturalists have doubted, and even denied that the 

 tentacle A\as anything more than a A-ery delicate oi-gan 

 of touch, yet it has been abundantly proved by dissec- 



