Walter Frank Raphael Weldon. XXXll 
_ characteristics of plants and animals,” and became transformed into an 
Evolution (Plants and Animals) Committee and Weldon and the biometric 
members ultimately withdrew from it. 
During the eight years of his London professoriate Weldon’s development 
was great; he became step by step a sound mathematician, and gained largely 
in his power of clear and luminous exposition. His laboratory was always 
full of enthusiastic workers, and over forty memoirs were published by his 
students. His removal from the London field of work, while an incalculable 
loss to his colleagues, was not without its compensation to his nearest friends. 
They knew that the life of the last few years had been one of great tension, 
that Weldon’s time had been too much encroached upon by committee work, 
that the separation between the locus of his teaching and of his research work 
was very undesirable; that even the social life of London involved too much 
expense of energy. He was a child of the’ open air and the breezes, and it 
was hoped that he might have more of them, if not in lowland Oxford, at 
least on the hills around. There was space and air too for the experimental 
work that had been so cramped in Gower Street. The Daphnia studies, which 
had oceupied so much energy under unfavourable conditions in London, were 
at once resumed on broader lines in the ponds and ditches round Oxford. 
With a basket of bottles attached to his cycle handle, and a fishing creel, 
filled with more bottles, on his back, the Linacre Professor might be met 
even as far as the Chiltern Hills, collecting not only Daphnia, but samples of 
the water in which they lived. His University College work had shown him 
how widely Daphnia are modified by their chemical and physical environment, 
and how this modification is largely due to selection. There exist elaborate 
drawings of the Daphnia from the Oxfordshire ponds, indicating their 
differentiation into local races, with notes on the peculiarity of their habitat 
and the chemical constitution of the water. 
A study of Kobelt’s “Studien zur Zoogeographie,” 1897-9, led him later to 
take up the same problem with regard to land-snails. What is the meaning 
of the slight but perfectly sensible differences in type to be found in shells 
from adjacent valleys or even from different heights of the same mountain ? 
Weldon attacked the problem in his usual manner; he spent two Christmas 
vacations collecting Sicilian snails of the same species, from habitats extend- 
ing over a wide area, the local environments were described, and the snails 
were often photographed with their immediate surroundings. Innumerable 
shells were brought back to Oxford, and the Professor delighted to discourse 
on the significant differences in local type, and yet the gradual change of type 
to type from one spot to another. No rapidly made measurement on the 
outside of the shell would satisfy him; the shell must be carefully ground 
down through the axis, and the measurements must be made on the section 
thus exposed. Perhaps four or five snail shells could be ground and measured 
in a day, and at the time of his death not more than a few hundred of the 
Sicilian thousands had even been ground. 
But these attempts to get to the kernel of selection in its action on local 
VOL. LXXX.—B. ad 
