{)2 bulletin: museum of comparative zoology. 



tangled and lack definite arrangement. This condition, which may 

 be called early leptotene (fig. 28), is followed by a later leptotene 

 (fig. 29), in w^hich the threads become oriented with one end attached 

 at one side (the polar side) of the nucleus. Soon there appear among 

 the single threads others which are double and twice the width of the 

 single ones. The proportionate number of double threads gradually 

 increases until all the threads appear double. The stage during w^hich 

 the doubling takes place (fig. 30, 31) is the zygotene stage of Gregoire 

 ('07). When all the threads have become double the pachytene stage 

 (Winniwarter, '00) has been reached (Plate 3, fig. 32-34). This term 

 continues to be applicable throughout the relatively long growth- 

 period, and until the spireme ^ breaks up into the haploid number of 

 segments, which become tetrads. The number of pachytene threads 

 seems to be much less than that of the leptotene threads. 



The stages characterized by the appearance of separate segments of 

 the spireme may be designated by the term diplotene of Winniwarter 

 ('00). This term is used for the sake of consistency with the others 

 employed, although the conditions in Phrynotettix differ somewhat 

 from those described by Winniwarter for mammals. He describes 

 the longitudinal split as disappearing in the pachytene stages, on 

 account of the threads becoming twisted, and reappearing in the diplo- 

 tene stage. In Phrynotettix the longitudinal split remains visible 

 and little or no twisting occurs. 



Soon after becoming independent, a second longitudinal split occurs 

 in the spireme segments at right angles to the first, thus forming 

 typical tetrads, each composed of four chromatids (McCIung, '00). 

 The first longitudinal split, which persists from the pachytene stage, 

 may be called the priviary split, and the one at right angles to it may 

 be called the secondary split. From the time of their formation until 

 the succeeding metaphase, the tetrads undergo a gradual shortening 

 and thickening. During this period they pass through the well- 

 known figures, X's, K's, 8's, rings and crosses (Plate 3, fig. 38). The 

 stage during which these changes occur is frequently referred to as 

 the diakinesis stage (Hacker, '95*), but it may be simpler to call it 

 the postspircine stage (Gregoire, '07), or the tetrad stage."^ 



The postspireme stages end with the establishment of the tetrad- 



' The term spireme will be used to embrace the stages included under the names leptotene, 

 zygotene, and pachytene without, however, implying anything as to the existence of a con- 

 tinuous thread. 



2 I have avoided the use of the term, prophase, in connection with the postspireme stages 

 because it might properly be applied to the whole series of stages from the preleptotene to the 

 metaphase. 



