il2 EVENINGS AT THE MICROSCOPE. 



to bathe its organs with as hirge a quantity of the fluid 

 as it can inhale. The pellucidity of all the integu- 

 ments will be thus greatly increased. A strong lamp- 

 light being now reflected, by means of the mirror 

 through the animal on the stage of the microscope, an 

 inch or a half-inch object-glass will probably reveal 

 tlie orifices in question with much distinctness. 



" The appearance of the cinclides may be compared 

 to that which would be presented by the lids of the 

 human eye, supposing these to be reversed ; the con- 

 vexity being inwards. Each is an oval depression, 

 with a transverse slit across the middle. When closed, 

 this slit may sometimes be discerned merely as a dark 

 line — the optical expression of the contact of the two 

 edges ; but, when slightly opened, a brilliant line of 

 light allows the passage of the rays from the lamp to 

 the beholder. From this condition the lids may sepa- 

 rate in various degrees, until they are retracted to the 

 margin of the oval pit, and the whole orifice is open. 



The dimensions of the cinclides vary not only with 

 the species, and probably also with the size of the 

 individual, but with the state of the muscular con- 

 traction of the integument, as, also, I think, with the 

 pleasure of the animal. In a small specimen of S. 

 dianthus, I found the width of a cinclis, measured 

 transversely, 275^^^^ of an inch ; but that of another, in 

 the same animal, was more than twice as great, viz., 

 y^flth of an inch. This was on the thickened marginal 

 ring, or parapet, which in this species surrounds the 

 tentacles, where the cinclides are larger than else- 

 where. Watching a specimen of S. nivea under the 

 microscope, I saw a cinclis begin to open, and grad- 

 ually expand till it was almost circular in outline, and 



