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INTRODUCTION TO CYTOLOGY 



univalents, if not already double, rapidly develop a longitudinal split, in 

 some cases even before they are entirely free from each other. The 

 resulting halves tend to open out along this split; chromosomes being 

 drawn endwise to the poles thus take the form of simple Vs, while those 

 to which the fibers are attached at the middle appear as double Vs. After 

 reaching the poles the split chromosomes begin the reconstruction of the 

 daughter nuclei. As a rule this does not proceed very far, since the 

 homceotypic mitosis follows very quickly upon the heterotypic. Well 

 organized daughter nuclei are often formed, whereas in the animal egg 

 there may be no reconstruction whatever, the daughter chromosomes of 

 the first mitosis at once taking their places on a newly formed spindle for 

 the second mitosis. 



In the homceotypic mitosis the chromosomes, if there has been an inter- 

 vening interkinesis of any length, usually appear much longer and thin- 

 ner than in the heterotypic mitosis, and separate along the longitudinal 

 line of fission seen in the preceding anaphase. The homceotypic mitosis 

 is therefore equational in character, and differs from an ordinary somatic 

 mitosis only in the number of its chromosomes and the precocity of their 

 splitting. In each of the four nuclei resulting from the two maturation 

 mitoses there is now the haploid number of univalent chromosomes, and 

 meiosis is complete. 



The foregoing interpretation of reduction has been widely accepted 

 from the first by both botanists and zoologists. The following is a partial 

 list of works in which it has been described. 



Plants 



Lilium, Allium, Osmunda 



Allium, Drosera, Helleborus, etc. 

 '08, '09 Drosera, Compositse 



Lilium, Coleochcete 



Thalictrum, Calycanthus, Richardia 

 '08, '09 Lilium, Galtonia, etc. 



Lilium, Funkia, Iris, Allium, Trades- 

 cantia, Galtonia 



Ribes 



Acer, Salomonia, Botrychium, Ginkgo 



Adoxa 

 '10 Polysiphonia. Nephrodium, Osmunda 



Funkia 



Trollius 



Myricaria 



Smilacina 



Thelygonium 



Xyris 



Vicia 



Polypodium 



