94 MEIOSIS IN DIPLOIDS AND POLYPLOIDS 



universal and takes place throughout the length where they are 

 paired and in any intercalary unpaired segments between paired 

 segments (D., 1935 a). Such a coiling must be due to a torsion in 

 the individual threads which, as will be seen, is expressed in various 

 other ways. 



Table ii 



Pristiurus (Pisces) $ ... 



Gryllus (Orthoptera) $ . . . 



Coelenterata, Annelida, Amphibia, etc., ? 

 Phanams (Coleoptera) 

 Alydus (Hemiptera) cj . . . 



Examples of a Diffuse Stage at Diplotene or Diakinesis 



Animals 



Riickert, 1892. 



Buchner, 1909. 



Jorgensen, 191 3. 



Hayden, 1925. 



Renter, 1930. Cf. Chickering, 

 1927 ; Wilson, 1928 et al. 

 Limnophilus decipiens (Trichoptera) $ and c? Klingstedt, 193 1. 

 Dasyurus (Marsupalia) ^ . . . . Roller, 1936. 



Plants 



Padina (Algae, Dictyotaceae) sporogenesis . Carter, 1927. 



Hyacinthus, ^ . . . . . . D., 1929 h. 



Tradescantia, ^ . . . . . D., 1929 c. 



Mitrastemon, ^ and $ . . . . Matsuura, 1935. 



Development is interrupted in some organisms during the 

 pachytene stage, or (especially in the eggs of Trichoptera and 

 Lepidoptera) later in the prophase, by the nucleus reverting partially 

 or entirely to a resting stage condition. This complication of 

 development, which has naturally hindered the interpretation of 

 successive stages, has been found in spermatogenesis in some 

 animals (e.g., Hemiptera, Wilson, 1912 ; cf. Chickering, 1927), 

 and in oogenesis in many more. In some species this change takes 

 the form of a swelling of the chromosomes, which continue the 

 normal course of development in their bloated condition [Pristiurus, 

 Riickert, 1892). In other species the chromosomes disappear for a 

 while and reappear again unchanged {Gryllus, Alydus, Mitrastemon). 

 In others again {Phanceus) a part of the nucleus containing the 

 chromosomes condenses to one side to form a " karyosphere," in 

 which the condensed pachytene chromosomes can be separately dis- 

 tinguished (see Table 11). These changes are inessential to meiosis ; 

 they appear to be determined by the special conditions of growth 

 of the cell and the nucleus at this stage of meiosis. They are not 



