. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. A Jack of All Trades 217 ing them by enormously large eyes adapted for catching the faintest glimmer of luminescence, so that when Diogenes of the Deep Sea fares forth, his lantern may not pass by unnoticed. Other deep-sea fishes, without light- producing organs, are usually entirely blind or have only very degen- erate eyes. Certain fishes, as well as amphibians and reptiles, also have integumen- tary cells of a glandular nature, called chromatophores, by
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. A Jack of All Trades 217 ing them by enormously large eyes adapted for catching the faintest glimmer of luminescence, so that when Diogenes of the Deep Sea fares forth, his lantern may not pass by unnoticed. Other deep-sea fishes, without light- producing organs, are usually entirely blind or have only very degen- erate eyes. Certain fishes, as well as amphibians and reptiles, also have integumen- tary cells of a glandular nature, called chromatophores, by means of which the color of the body may be modified to conform to the color of the environment in which the animal temporarily finds itself. It has been dem- onstrated by Parker that the operation of these color changes depends not so much on direct stimulation through the nervous system as upon certain "neurohumors" or hormones produced by ductless glands within the body. With the exception of the so-called Leydig's glands found in the larvae of some anurans, one-celled epidermal glands, so characteristic of the fish skin, do not appear in amphibians, being replaced by many-celled alveolar glands which also provide mucus. One of the functions of the skin glands of both fishes and amphibians, that does not recur as an integumental activity in higher vertebrates, is the production of irritating or poisonous substances as a means of defense against enemies. In fishes such poison glands are usually at the base of punc- turing spines or sharp fin rays, but in amphibians they are more generally dis- tributed over the body. Toads, for ex- ample, are usually left alone on account of the noxious secretions from their skin glands. The glandular rings that alter- nate with the tiny embedded scales of the blind caecilians are equipped not only with many-celled mucous glands, characteristic of amphibians, but also with peculiar giant poison glands (Fig. 148). Another function o
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