. The biology of the amphibia. Amphibians. 368 THE BIOLOGY OF THE AMPHIBIA eye of the growing tadpole brings about marked reduction in the midbrain (Durken 1912). The converse experiment of building up the brain by increasing a sensory area has been performed on Ambystoma. Burr (1922) transplanted the large olfactory placode of Ambystoma tigrinum on the small A. maculatum and obtained an increase in the number of cells of the cerebral hemi- sphere of the host. This increase extended to the secondary and tertiary nuclear centers. Thus, axons growing into embryonic Fig. 128.—Amphibian brains, do
. The biology of the amphibia. Amphibians. 368 THE BIOLOGY OF THE AMPHIBIA eye of the growing tadpole brings about marked reduction in the midbrain (Durken 1912). The converse experiment of building up the brain by increasing a sensory area has been performed on Ambystoma. Burr (1922) transplanted the large olfactory placode of Ambystoma tigrinum on the small A. maculatum and obtained an increase in the number of cells of the cerebral hemi- sphere of the host. This increase extended to the secondary and tertiary nuclear centers. Thus, axons growing into embryonic Fig. 128.—Amphibian brains, dorsal view. A. Adult Pipa pipa. {After Griinberg.) B. Larva of Hynobius nebulosus. (After Sumi.) C. Adult Hypo- geophis rostratus. (After Kuhlenbeck.) C, cerebellum; , eminentia medialis rhombencephali; Ep., epiphysis; F., fossa rhomboidea; H., lobus hemisphaericus; M., mesencephalon; , cranial nerves I-XI; O., nervus olfactorius; Par., paraphysis; , sulcus longitudinalis centralis; , sulcus rhinalis anterior; , sulcus transversus diencephalo- mesencephalicus; T., thalamus. brain tissue are potent factors in the further elaboration of the brain. Such experiments are very suggestive of the way the brain was built up during phylogeny. An increased growth in one center might have a corresponding effect on another. An equally important change in phylogeny was the grouping of nerves of related functions in discrete areas. Such a progressive change has only well begun in the Amphibia. In the higher vertebrates there is an attraction of most of the somatic connec- tions to the striatum and later their projection to separate centers on the pallium. Such a brain is far better adapted both for. A B c. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Noble, Gladwyn Kingsley, 1894-1940.
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Keywords: ., bookcentury1900, bookpublishernewyorkmcgr, booksubjectamphibians
