236 



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 

 horn ceoty pic 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 



Gr6goire 1904, '07 Lilium, Allium, Osmunda 



Berghs 1904, '05 Allium, Drosera, Hetteborus, etc. 



Rosenberg 1905, '07, '08, '09 Drosera, Composite 



Allen 19056c Lilium, Coleochcete 



J. B. Overton 1905, '09 Thalictrum, Calycanthus, Richardia 



Strasburger 1905, '07, '08, '09 Lilium, Galtonia, etc. 



Miyake 1905 Lilium, Funkia, Iris, Allium, Trades- 



cantia, Galtonia 



Tischler 1906 Ribes 



Cardiff 1906 Acer, Salomonia, Botrychium, Ginkgo 



Lagerberg 1906, '09 Adoxa 



Yamanouchi 1906, '08, '10 Polysiphonia, Nephrodium, Osmunda 



Martins Mano 1909 Funkia 



Lundegardh 1909, '14 Trollius 



Frisendahl 1912 Myricaria 



McAllister 1913 Smilacina 



Schneider 1913, '14 Thelygonium 



Weinzieher 1914 Xyris 



Sakamura 1914 Vida 



de Litardiere 1917 Poly-podium 



