iQ2o] CURRENT LITERATURE 89 



spirem of the somatic prophase; the doubleness is believed to be the result of 

 splitting in the last premeiotic telophase, and not to a conjugation of entire 

 chromosomes. This double univalent spirem, which is more or less conspicu- 

 ously beaded according to the fixing agent employed, is soon thrown into 

 loops and the split becomes obscured. During the succeeding stages segments 

 of the spirem (the "filaments"), although originally arranged end to end 

 before segmentation, conjoin laterally in pairs to form the bivalent chromo- 

 somes, a process which is consummated in the second contraction. It is here 

 that the conjugation of entire chromosomes occurs, whereas at the first con- 

 traction (synizesis) daughter halves of chromosomes are reassociated. As the 

 second contraction loosens, the bivalents shorten and thicken and take up 

 positions near the periphery of the nucleus (diakinesis) . Only rarely at this 

 stage can the temporarily obscured split of each component of the bivalent 

 be detected. 



As the bivalent takes its place upon the spindle, its univalent components 

 become somewhat disjoined, and each again reveals the fission which had its 

 origin in the last premeiotic telophase and was most conspicuous in the spirem 

 of the early heterotypic prophases, and which marks the line of separation for 

 the homotypic mitosis. As the univalent passes toward the pole, its halves 

 widen out along this line of fission, giving the v-form characteristic of the 

 heterotypic anaphase. During early telophase each daughter half of the split 

 univalent undergoes a new longitudinal fission; this is homologous with the 

 split occurring in the somatic telophase; after being obscured it reappears in 

 the homotypic anaphase and functions in the post-homotypic division. The 

 telophasic transformation of the chromosomes occurs as described for the 

 archesporial divisions, and during interkinesis the individual chromosomes are 



indistinguishable. 



The homotypic division is regarded as essentially a continuation of the 

 last premeiotic division, since the doubleness of the chromosomes of the 

 homotypic prophase is held to be the same as that of the last premeiotic 

 telophase; the heterotypic division is consequently an interpolated process 

 effecting numerical reduction. Although the events of the homotypic division 

 are "involved in some obscurity, " they seem to be in the main as follows. The 

 threads derived from the fission of the daughter halves of the univalent 

 chromosomes in the heterotypic telophase reassociate in pairs and form a 

 number of chromatic masses, which later take the form of loosely associated 

 daughter univalents; these arrange themselves more or less independently on 

 the spindle. During their anaphasic separation (along the line marked out 

 in the last premeiotic telophase) the fission which had its origin during the 

 close of the heterotypic mitosis, and which is to function in the post-homotypic 

 mitosis, reappears. The chromosomes at telophase take the form of double 

 beaded threads which establish the resting reticulum as in the archesporial 

 mitoses. 



