172 NOTES AND EXHIBITS. 



interested; and his kindness and courtesy in supplying collec- 

 tions, and affording information, have been of great service to 

 ornithologists. 



Discussion. — Mr. Tillyard gave a short explanation of his pro- 

 posed method for the "Study of Zoo-geographical Distribution by 

 means of Specific Contours." In this method, instead of attempt- 

 ing to subdivide the recognised zoogeographical regions into dis- 

 tinctly marked off sub-regions and lower divisions, it is proposed 

 to study the various groups of plants or animals occurring over 

 the whole region, by constructing "specific contours" by the follow- 

 ing rules. (l)The group selected must be a natural group, i.e., 

 a genus, tribe, or family which forms a homogeneous whole, and 

 not merely a group separated off for convenience of classification. 

 (2) The records available must be sufficiently numerous to give 

 the general form of the contour, but absolute accuracy is neither 

 attainable (without infinite labour) nor necessary. (3) Each 

 species of the selected group is reckoned as a unit. On the map 

 of the region under study, against each locality which has been 

 "worked," the number of units occurring there is to be put down. 

 Then contour lines, in the form of free curves, are to be drawn so 

 that all localities having an equal number of units shall be between 

 any two successive contour-lines. Clearly, the higher the number, 

 the smaller the area enclosed by the contour, and vice versd. The 

 first contour line is the outer boundary of distribution for the 

 group. The nth. or highest contour encloses an area termed the 

 "Zoo-centre" or, if elongated in form, the "Zoo-centric Axis." By 

 examination and classification of the different forms of contour 

 obtainable over any given region Z, it will be evident that there 

 are three main divisions : — 



A. Entogenic Contours with the Zoocentres lying within Z and 

 their lower contours spreading out around it. Groups of this kind 

 furnish the characteristic fauna or flora of the region. 



B. Ectogenic Contours with their Zoocentres lying quite outside 

 or near the boundary of Z., and having lower contours spreading 

 more or less into Z. Groups of this kind are outgrowths from the 



