THE LOBSTER AS A TYPE OF CRUSTACEA 31 



A still more remarkable change sometimes occurs 

 when one of the eye-stalks is injured. If only the tip 

 of the eye-stalk be cut off, so that the nerve-ganglion 

 which lies in the basal part of the stalk remains 

 uninjured, it will be found that a normal eye is in 

 course of time regenerated. If, however, the whole 

 eye-stalk be amputated, and with it the optic ganglion, 

 there grows in its place, not a new eye-stalk, but a 

 segmented appendage similar to one of the flagella of 

 the antennules. This fact is considered by some 

 zoologists to indicate that the eye-stalks are, like the 

 antennules, true appendages, homologous with the 

 mouth parts and limbs, but this is a much-disputed 

 question into which we cannot enter further here. 



Lobsters vary a good deal in colour, but as a rule 

 a living Lobster is of a more or less mottled dark blue* 

 becoming nearly black on the back, and shaded off 

 into orange yellow or red on the under-side. This 

 coloration resides in the shell, and does not change 

 much after the shell has hardened. In this respect 

 the Lobster is unlike many of the smaller Crustacea 

 which have a thin and more or less transparent 

 exoskeleton, and in which the colour resides in certain 

 living cells (chromatophores) of the underlying 

 skin. Many of these Crustacea possess the power 

 of changing their colours to a remarkable degree, 

 by the expansion and contraction of the branched 

 chromatophores. 



The question which is often asked, " Why does a 



