Outlines of scientific anatomy : for students of biology and medicine / by Wilhelm Lubosch ; translated from the German by H.H. Woollard.

  • Wilhelm Lubosch
Date:
1928
Catalogue details

Licence: Public Domain Mark

Credit: Outlines of scientific anatomy : for students of biology and medicine / by Wilhelm Lubosch ; translated from the German by H.H. Woollard. Source: Wellcome Collection.

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    whole material reckon all the angular appearances of the chromosomes as artefacts, and regard only perfectly smooth chromosomes as representing the natural condition. The newer investigations criticize these statements. It is certain in each case that in the resting nucleus the chromioles do not remain intact and unchanged in their areas. Active metabolic processes and shifting of position occur. It is certain that they undergo in part transformation and renewal so that the chromosomes arising in the region of the resting nucleus, which in a gross view must be regarded as identical, are certainly not materially identical in respect to their finer structure. (iii) Chromosomes (“ Genomes ”) and the Formation of Species. Para. 116. Here now we must proceed with quite special care, for cautious consideration will at once make it clear that in the last resort the changeability of form, species formation, which, as we learnt above [para. 32 G] is the source of transformation, is with difficulty reconciled with the unchangeability of the chromosomes. We have numerous approaches now for the appreciation of this relation from whose perfect explanation we are still very far distant. In a descriptive view the different sizes and forms of the chromo¬ some groups of a species are very remarkable. If, for example, there are 1-4 chromosomes, then in all the body cells chromosome 1 agrees with 1 and likewise 2, 3 and 4 (the whole group is then the “ genom ”). Comparing different races of the same species one often observes differences of identical chromosomes in respect to their size and form (e.g., in the chromosome number 1). In the comparison of different species such differences are present in marked degree. They can go as far as the degeneration of a chromosome into a small fragment, even to its disappearance, so that the chromosome number within a species of a genus exhibits a typical diminution. An extensive survey on the number of chromosomes in the classes, orders, species, varieties of plants, the reader will find in Tischler ; besides numerous estimates for animals (cf. also chapter, Species, and the Maturation of the Ovum, in Lubosch, 1913). On the other hand, experiment has shown that changes in the state of the genom (increase and diminution) influence hereditarily the developing organism (giant or dwarf forms, p. 359). Also increase or diminution of a particular chromosome experimentally produced leads to changes of body size. So there arises quite certainly a relation between the genoms and the form of the organism and between the unfolding of one and the other. We can only follow those changes which are of a quantitative kind in the genoms at the moment. However, in view of the whole
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