504 ADAPTATIONS TO PHOTIC QUALITY 



pollination. Less common, but still very numerous among bird-flowers, 

 are blue-flowered species. Porsch relates the abundance of red-flowered 

 bird plants to the birds' high sensitivity to red (which has been experi- 

 mentally demonstrated for humming-birds), suggesting that the red of 

 the flower is an identification mark which the bird can pick out from a 

 great distance, and which remains maximally visible against the foliage 

 even in the auroral and crepuscular hours. He raises the question 

 whether flower-visiting birds may not have man-like or superhuman sensi- 

 tivity to blue light as well as to red — assuming that the plants have actu- 

 ally adapted their flower colors to fit the visual spectra of the birds upon 

 which they depend. Obviously, in the evaluation of avian oil-droplet 

 color mosaics and patterns of spectral responsivity, in ecological terms, 

 the surface has scarcely yet been scratched. 



Mammals — Within the mammals, color vision is by no means wide- 

 spread, as it is in fishes, reptiles, and birds. To a large degree this is sim- 

 ply an expression of the fact that strong diurnality is uncommon in mam- 

 mals. But, not even all diurnal mammals have color vision. This would 

 be particularly hard to understand if the few diurnal mammals were all 

 primitive and stood closer than other mammals to the reptilian stem. The 

 birds, for instance, clearly owe their chromatic vision to direct, unbroken 

 inheritance from reptiles — possibly avian color vision traces back through 

 the reptiles to the Stegocephali, or even back through them to the fishes 

 (Fig. 156, p. 519). 



The indications are, however, that on the road of mammalian evolu- 

 tion there was a considerable stretch of achromatic noctumality between 

 the color-seeing reptiles and the first color-seeing placental mammals. 

 Strong or strict diurnality, backed up by a cone-rich or pure-cone retina, 

 is not a primitive habit of mammals. Nor can it be said that diurnality 

 has arisen in the mammals only as one of the specializations and points- 

 of-superiority of the 'highest' forms. Though the larger ungulates and car- 

 nivores tend toward diurnality, in that they have become arhythmic from 

 nocturnal beginnings, it is only the squirrel and monkey tribes which pre- 

 sent fully diurnal members. The squirrels are rodents, which rank fairly 

 low — but even they must be given rank above us, in point of 'special- 

 ization' and 'modernity'. We, as primates, adjoin the very lowest of all 

 the orders of placental mammals, the Insectivora. All of our domestic 

 animals roost far higher in the taxonomic tree than we ourselves — a point 

 which is overlooked by some writers on comparative ophthalmology, who 



