620 CHROMATOPHORES OF CEPHALOPODS. 



under the Microscope, and transmitting a strong light through it. 

 The very early appearance of the Auditory Vesicles in the Embryo 

 Gasteropod has been already alluded-to (§ 477). — Those who have 

 the opportunity of examining young specimens of the common 

 Pecten, will find it extremely interesting to watch the action of the 

 very delicate tentacles which they have the power of putting-forth 

 from the margin of their mantle, the animal being confined in a 

 shallow Cell, or in the Zoophyte-trough; and if the observer should 

 be fortunate enough to obtain a specimen so young that the valves 

 are quite transparent, he will find the spectacle presented by the 

 Ciliary movement of the Grills, as well as the active play of the Foot 

 (of which the adult animal can make no such use), to be worthy of 

 more than a cursory glance. 



483. Chromatophores of Cephalopods. — Almost any species of 

 Cuttle-fish (Sepia) or Squid (Loligo) will afford the opportunity of 

 examining the very curious provision which their Skin contains for 

 changing its hue. This consists in the presence of numerous large 

 'Pigment-Cells,' containing colouring matter of various tints ; the 

 prevailing colour, however, being that of the fluid of the Ink-bag. 

 These Pigment-cells may present very different forms, being some- 

 times nearly globular, whilst at other times they are flattened and 

 extended into radiating prolongations ; and, by the peculiar con- 

 tractility with which they are endowed, they can pass from one to 

 the other of these conditions, so as to spread their coloured con- 

 tents over a comparatively -large surface, or to limit them within 

 a comparatively-small area. Very commonly there are different 

 layers of these Pigment-cells, their contents having different hues 

 in each layer ; and thus a great variety of coloration may be 

 given, by the alteration in the form of the cells of which one 

 or another layer is made-up. It is curious that the changes in the 

 hue of the Skin appear to be influenced, as in the case of the 

 Chameleon, by the colour of the surface with which it may be in 

 proximity. The alternate contractions and extensions of these 

 Pigment-cells or Chromatophores may be easily observed in a 

 piece of Skin detached from the living animal and viewed as a 

 transparent object; since they will continue for some time, if the 

 skin be placed in Sea-water. And they may also be well seen in 

 the Embryo Cuttle-fish, which will sometimes be found in a state 

 of sufficient advancement in the grape -like eggs of these animals 

 attached to Sea-weeds, Zoophytes, &c. — The Eggs of the small Cuttle- 

 fish termed the Sepiola, which is very common on our southern 

 coasts, are imbedded, like those of the Doris, in gelatinous masses, 

 which are attached to Sea-weeds, Zoophytes, &c. ; and their Em- 

 bryoes, when near maturity, are extremely beautiful and interesting 

 objects, being sufficiently transparent to allow the action of the 

 Heart to be distinguished, as well as to show most advantageously 

 the changes incessantly occurring in the form and hue of the 

 Chromatophores. 



