566 APPENDIX I 



particles in it. (v) The anastomosed structure seen in the resting 

 nucleus by Sharp and Martens is non-characteristic. It cannot be 

 related to structures seen earlier or later (Ch II). 



Having excluded non-characteristic artefacts, we may then consider 

 the significance of different kinds of characteristic artefact. The 

 comparative method at once shows us that some correspond closely with 

 living conditions, e.g., the chromomere structure, while others are 

 definitely abnormal and peculiar to the effects of treatment on certain 

 organisms, e.g., the contraction in the prophase of meiosis. 



The artefactual nature of the spiral structure of the chromosomes 

 seen in smear preparations of metaphase, particularly of meiosis, is 

 shown by the optical homogeneity of the living chromosomes. Its 

 characteristic nature is shown by its relationship with uncoiled pre- 

 treated spirals as well as with relic spirals at the following telophase 

 and prophase. It depends, therefore, on a characteristic and artefactual 

 differentiation of the chromosome into staining and non-staining parts. 

 The products of this differentiation have been named " chromonema " 

 and " matrix " and have been given a developmental significance. 

 Such a significance they cannot have in view of their artefactual nature. 

 They depend on the different types of coagulation to which chromo- 

 somes, like milk, are subject. The matrix is the whey, which is separated 

 from the curd by fixation. It does not exist morphologically or 

 mechanically until the chromosomes are fixed, however useful its 

 distribution may be in enabling us to determine what the internal 

 structure of the chromosome may be. In its use to fill a morphological 

 and mechanical role in the living chromosomes the word matrix is 

 nothing more than a myth (D., 1935 e). 



Genetical inferences are subject to other kinds of error. They are 

 derived from observations of mitosis and meiosis. In mitosis assump- 

 tions are made which are correct except for certain exceptional cases. 



(i) It is assumed that the chromosome complement seen at one 

 division is characteristic of the individual and even of the species. The 

 exceptions to this rule (based on the theory of permanence) are so few 

 that it can be satisfactorily applied in practice unless there are a priori 

 reasons for expecting lack of constancy (as in the examination of 

 mutants or geographical races). 



(ii) It is assumed (also on the basis of the theory of permanence) that 

 differences between species in the size of their chromosomes will be 

 maintained in their hybrids and derivatives. The observations 

 described earlier (Ch. Ill) show that this conclusion is not necessarily 

 true, although experimental evidence is still confined to few and 

 exceptional cases. Since genetic properties influence chromosome size 

 and length where two related species have chromosomes of different size 

 or length but are otherwise comparable, it is rather to be assumed that 



