aroLLuscA : their eyes. 57 



possbss. i'ou see on cacli tentacle a little wart, "^vliich 

 when YOU look at it with a lens you perceive to have 

 a round black glossy extremity. This is the eye. By 

 careful dissection under the microscope, we find it to 

 contain a beautiful transparent crystalline lens, with a 

 thick and glutinous vitreous humour adhering to it be- 

 hind, bounded by a retina or curtain to receive the op- 

 tic 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 oper- 

 cularis\ much prized for its delicate sapidity. Belong- 

 in 2: to the bivalve class of the Mollusca, the animal is 

 inclosed within two shallow shelly plates, concave in- 

 ternally, 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 clear, it lies on one side, 

 its valves being separated as we see them now, a quar- 

 ter of an inch or so apart, allowing us to discern what 

 is contained between them. 



"Well, we see first a number of slender, white-pointed 

 threads, peeping out from each valve and spreading on 

 all sides, waving hither and thither, groping, now con- 

 tracting, now expanding, with incessant but deliberate 

 motion. Tliesc are tentacles. If we trace them to 

 their origin, we find them attached to a fleshy sort of 

 veil that lines each valve to near its edge, and then ab- 

 ruptly falls at an angle towards the opposite valve, 

 where it meets a corresponding veil. These two veils 

 form the mantle. It is from each of these that the ten- 

 tacles spring ; and we discover that there are fuur rows 



