234 Miscellaneous. 



Lacerta muralis casrulea : a Contribution to the Darwinian Theory. 

 By Dr. Theodor Eimer. 



On the south-east coast of the Isle of Capri four large rocks may 

 be remarked with a very picturesque aspect, three of which are en- 

 tirely separated from the land, while the fourth is only joined to it 

 by a small low and narrow isthmus, which threatens also to disappear 

 under the action of the waves. The outermost of these islets is in 

 the form of a truncated pyramid with four sides, 115 metres high, and 

 terminated above by a small plateau containing about 50 square 

 metres. Its sides are nearly vertical, and, in consequence, nearly in- 

 accessible. There are only three inhabitants of Capri who venture 

 to climb it, for the purpose of gathering the eggs of sea-gulls. 



In the spring of the year 1872 M. Eimer applied to these men in 

 order to procure specimens of the animals which live on this little 

 islet, to ascertain whether the conditions of isolation had not ex- 

 ercised some influence on them. 



His prevision was verified, for his collectors brought him a lizard 

 forming a very remarkable variety of the common species {Lacerta 

 muralis) of the Isle of Capri. This variety is even so distinct from 

 the type that in the eyes of many zoologists it might be regarded as 

 a species. 



M. Eimer has made a complete study of this form, which exists 

 only on the rock in question, and to which he has given the name 

 of Lacerta muralis ccerulea ; and he compares it with the different 

 varieties of L. muralis which are met with in Capri, in the Kingdom 

 of Naples, at Genoa, and in Germany. 



It is by its colouring that the variety ccerulea is distinguished in 

 the most striking manner. The colour of the dorsal parts is some- 

 times of a uniform more or less deep blue, sometimes blue with black 

 markings. The belly, the throat, the lower jaw, and the lower sur- 

 face of the tail and limbs are of a magnificent deep sky-blue. This 

 colouring presents certain modifications depending on the season, the 

 temperature, sex, &c. Thus at certain periods of the year emerald- 

 green eye-spots make their appearance. 



The colour does not result from a deposit of blue pigment, but it is 

 due to the existence of a thick coat of black cells of connective tissue 

 which are placed under a likewise thick coat of colourless epidermis. 

 This arrangement, as is well known, produces the impression of blue. 

 By direct fight under the microscope a fragment of skin appears 

 black ; by reflected light it is seen to be blue. In the green lizards 

 there is, between the black layer and the colourless layer, a layer of 

 yellow pigment of a fatty nature, which assists in producing the im- 

 pression of green. In L. muralis ccerulea this yellow coating is ab- 

 sent or is nearly so. 



A constant peculiarity of the L. muralis of Germany is the de- 

 pressed form of the head. This character is not found in the variety 

 ccerulea, of which the head forms rather a quadrangular pyramid 

 with nearly equal sides. 



The new variety differs less from Italian individuals than from 

 those of Germany ; but it is distinguished from them nevertheless. 



