Horizontal gene transfer and the evolution of cnidarian stinging cells

for detecting the crowding of texture are both at play. Disentangling the two will be an interesting challenge. One promising line, as Durgin [8] suggests, will be to look for dissociations between number and texture perception. Manuela Piazza, Stanislas Dehaene and Marco Zorzi (personal communication) have shown that dyscalculic individuals have higher Weber fraction for number discrimination than do controls. It would be interesting to study whether discrimination of texture is also affected in these individuals; and to test adaptation to both attributes. We suspect that the investigation of numerosity as a visual primitive will open a rich vein of connections between visual perception and mathematical intuition. Mathematicians often ‘see’ their solutions first and verify them later, as many testified to Hadamard [15].