50 EVENINGS AT THE MICROSCOPE. 



running round like an endless band in some piece of 

 machinery ; only that the tooth points, as they run by, 

 remind one rather of a watch- wheel. For an instant this 

 appears, then the lips close again, and presently re-open, 

 and the tongue again performs its rasping. It is wonder- 

 ful to see ; perhaps not more wonderful than any other 

 of God's great works, never more great than when 

 minutely great ; but the action and the instrument, the 

 perfect way in which it works, and the effectiveness with 

 which the vegetation is cleared away before it, all strike 

 the mind with more than usual force, as exhibitions of the 

 skill of the Creator. 



As the Periwinkle moves along, mowing his sea-grass as 

 he goes, he carries before him two soft and flexible horns, 

 marked with zebra-like bands of black and white, which 

 he constantly waves about. These are organs of some 

 sense, probably of touch, and are therefore called tentacles 

 (or tryers) ; but they bear on their outer sides, near the 

 base, a pair of other organs, which are more closely 

 analogous to what we ourselves possess. You see on each 

 tentacle a little wart, which, when you look at it with 

 a lens, you perceive to have a round black glossy ex- 

 tremity. This is the eye. By careful dissection under 

 the microscope, we find it to contain a beautiful trans- 

 parent crystalline lens, with a thick and glutinous vitreous 

 humour adhering to it behind, bounded by a retina or 

 curtain to receive the optic image, and an optic nerve. 



But much more attractive you will find the eyes in this 

 little Scallop. It is a half-grown individual of what is 

 provincially known as the Squin (Pecten opercularis), 

 much prized for its delicate flavour. Belonging to the 

 bivalve class of the Mollusca, the animal is inclosed 

 within two shallow shelly plates, concave internally and 

 convex externally, which are united by a hinge, just as the 

 works of a watch are protected by the case. When the 

 little creature is at its ease, as when the water is pure and 



