ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



177 



the lots are arranged in the order a, b, c, in which a and c are the geo- 

 graphical extremes, they are found to be the biological extremes also. 

 iy "Where the environmental conditions of the isolated form units 

 are similar, the differences met with are easily accounted for on the 

 assumption of mutations which are preserved. Where, on the other 

 hand, the environmental conditions are dissimilar, it is obvious that 

 they must produce a change either through their " direct and definite " 

 action or possibly by selection. To deny that environment may act 

 directly to produce profound, eventually specific changes is to deny the 

 evidence of some of the best experimental work in evolution, and this 

 experimental work has also proved the inheritance of these environ- 

 mentally induced changes. The mutation theory errs, then, in stating 

 only a half truth. Through mutation, and also through the direct 

 action of environment, specific changes may be produced." 



Origin of Fine Pearls.* — L. Boutan maintains that there is no real 

 distinction between nacreous pearls formed external to the mantle like 

 the shell, and fine pearls, said to be formed within the tissues of the 

 mantle. Experiments have convinced him that in all cases the pearl, 

 which is provoked by the presence of a parasitic fluke, as has been pre- 

 viously shown, has an epithelial origin, and represents a secretion of the 

 external epithelium of the mantle. When it becomes possible by artificial 

 trepanning of the shell to imitate precisely the penetration of the fluke, 

 the production of true pearls will be Avithin human control. 



Arthropoda. 



Classification of Arthropoda.| — A. S. Packard discusses in an in- 

 teresting paper the affinities and evolution of the Arthropods, which he 

 regards as forming a polyphyletic group. His general conclusions may 



be inferred from the scheme which he suggests. 



Insecta 

 Arachnida Sjmjhyla 



Crustacea 



MeroBtomata Diplopoda Chilopoda 



Trilobita 



Pauropoil 



Malacopoda 



Palteopoda 



Protagnostus 

 (Protaspis) 



Annelida 



II 

 Pancarida 



III 



Merupoda 



IV 



1 'rotracheata 



V 



Entomoptera 



Annelida 



or 



Troehosphaera 



Annelida 



Annelida 



* Cornptes Rendus, oxxxvii. (1908) pp. 1078-5. 



t Proe. Amer. Phil. Soc., xlii. (1903) pp. 142-G1 (1 fig.). 



