162 BRITISH APHIDES. 



resembles amber, is, though perhaps not exclusively, 

 the produce of the Mexican Rhus cop allina. Its sp. 

 gr. is 1'39. Resin amine" is easily scratched, has a sp. 

 gr. of 1'35, and is the produce of Ilymencea cowr- 

 ba/ril. This last resin is exceedingly rich in enclosed 

 insect remains ; but I have been unable as yet to dis- 

 cover amongst the many specimens kindly lent for my 

 inspection any trace of Aphides. As both these resins 

 are of tropical origin, their absence need not cause any 

 surprise. 



It is probably due to the fact that so many kinds of 

 fruit, seed, and woody fragments have been embedded 

 in amber, that such discordant views have been 

 advanced as to its origin. The resin has been referred 

 at different times to the oak, the poplar, and even to 

 the palm-tree. 



From the peculiar character of the cellular tissue 

 entangled in the masses, Prof. Goeppert refers the 

 exudation to an extinct conifer, to which he gives the 

 name Finns succinifer. This is now generally believed 

 to be the true source of amber ; although, from the fact 

 that other conifers are to be found associated with the 

 amber masses, it is not certain that the excretions have 

 but one single origin. 



There are several allied resins of different densities ; 

 and probably they represent eras of different geological 

 times. We have ambrite from New Zealand, walcho- 

 wite, copalite, schlerotinite, and damar.* 



The examination of insects enclosed in resins of such 

 high refractive power as amber and copal presents some 

 difficulty. The rounded masses often act as lenses, and 

 so scatter the light that the microscope can be rarely 

 used until the specimens have undergone some mani- 

 pulation. The most obvious and efficient mode is that 

 of slitting and polishing the masses by aid of the lapi- 

 dary's wheel. This is somewhat troublesome and 

 costly, and has the disadvantage of injuring masses 

 valued for ornament. 



* J. D. Dana, ' Manual of Mineralogy and Lithology,' 1879. 



