1893.] Mr Bateson, On numerical Variation in Digits. Gl 



(2) On numerical Variation in Digits, in illustration of a prin- 

 ciple of Symmetry, by W. Bateson, M.A., St John's College. 



Abstract. 



An account was given of cases of Variation in number of digits 

 so occurring that the parts are symmetrical about a new axis in 

 the limb. Of these the plienomena seen in the bones of a number 

 of polydactyle Cats were chiefly important. The normal hind foot 

 of the Cat has four toes, each bearing a claw retracted by an 

 elastic ligament to a notch on the external side of the second pha- 

 lanx. This circumstance differentiates digits formed as lefts from 

 those formed as rights. As extra digits are added on the internal 

 side of the limb the symmetry changes. The limb being taken as a 

 right, the variations seen are as follows. (1) Hallux present, making 

 five digits : index is then in form intermediate heUveen right and 

 left. (2) Six digits present, internal having two phalanges : the 

 three external digits are then normal rights, the next two are lefts; 

 the internal, having a non-retractile claw, is indifferent. (3) Six 

 digits present, internal having three fully-formed phalanges and 

 retractile claw : the three externals are then normal rights, and 

 the three internals are left digits, thus forming two groups in 

 bilateral symmetry about an axis passing between the digits 

 having the relations of index and medius. Several cases of 

 " double hand " in Man form a similar progressive series, and 

 analogous facts in other animals were instanced. 



Monday, March 13, 1893. 



Prof. T. M^K. Hughes, Peesident, in the Chair. 



H. K. Anderson, M.A., Gonville and Caius College, was elected 

 a Fellow of the Society. 



The following Communications were made to the Society : — 



(1) On a compound of gold and cadmium. By C. T. 

 Heycock, M.A., King's College. 



(2) On the Spectra of electric discharges ivithout electrodes 

 through gases. By H. F. Newall, M.A., Trinity College. 



(3) Exhibition of some p)hotographs of the Solar Spectrum 

 by Mr Geo. Higgs. By R. T. Glazebrook, M.A., F.R.S., Trinity 

 College. 



(4) An experiment on the vibrations of a spiral spring. By 

 L. R. Wilberforce, M.A., Trinity College. 



