442 
GEOFFREY SMITH AND EDGAR SCHUSTER. 
smooth, even surface from which the epidermal papillae have 
almost entirely disappeared (fig. 32). Thus duriug the 
months when the most active growth of the testes is taking 
place the thumb-pads remain apparently inactive and smooth. 
In August and September the epidermal papillae begin to be 
obvious, and from this time onwards until about February a 
continuous increase of the epidermal papillae and pigmentation 
occurs. During the greater part of the time when the thumb- 
pads are attaining their characteristic rough and pigmented 
appearance the testes remain inactive and unchanged — a fact 
which has been too readily overlooked by writers on the 
correlation of the primary and secondary sexual characters. 
Although the above statement with regard to the thumb is 
roughly correct, a careful examination of the thumbs under a 
dissecting microscope of a series of male frogs throughout the 
year reveals much individual variability, and brings out one 
fact which is of prime importance in the interpretation of 
certain experimental results (see Table, p. 468). It will be 
noticed from the table, which refers to male frogs caught wild 
during the year December 5th, 1910-November 7th, 1911, that 
when the thumb-pad is thrown off after the breeding season in 
March or April, the thumb does not necessarily at once become 
perfectly smooth and unpapillated. Small, though quite 
marked, colourless papillae may be retained on the pad, which 
denote the bases of the old prominent pigmented papillae 
present in the breeding season (cf. Text-figs. A and B). It 
was not until June, July and August that the majority of male 
frogs had quite or nearly smooth pads (Text-fig. C), and 
even during these months small papillae were observable in a 
certain number of specimens. During September all the 
frogs observed had begun to develop the papillae again to a 
marked extent, and from this month onward the increase in 
size of the papillae was continuous up to the breeding season. 
The disappearance of the papillae after the breeding* season 
is therefore not a sudden or complete disappearance, but 
takes place gradually and at different rates in different 
individuals during the summer months. It is perfectly true 
