GERM CELLS IN ASCARIS INCURVA 65 



finer threads are also occasionally observed. In some speci- 

 mens the pachyteme threads resemble somewhat the condition 

 found in oogenesis (page 68) but this occurs more often in 

 material in which the fixation is manifestly inferior. The pachy- 

 tene stages do not show a conspicuously looped bouquet stage 

 but this is due to the fact that the looped threads extend to 

 the nuclear wall where their course cannot be followed. Later 

 the rigidity is relaxed (fig. 12), threads become somewhat loos- 

 ened from the plasmasome and in cross section they show a 

 quadripartite structure, the sections approximating a square 

 and showing a tendency for the chromatin to mass at the cor- 

 ners. The threads next become longitudinally cleft — the parts 

 separating and twisting upon each other thus forming a diplo- 

 tene nucleus (fig. 13). The double threads sometimes show a 

 second longitudinal cleft. The nucleus then enters a long 

 continued, lightly staining 'diffuse' stage (fig. 14) in which the 

 structure of the threads may only occasionally be observed. 

 Linin threads bearing chromatin irregularly distributed tra- 

 verse the nucleus, lie on the inner surface of the nuclear wall 

 or upon the plasmasome. 



Throughout the growth period the plasmasome increases 

 in size (figure 13 shows a portion only) and the chromatin threads 

 interlace upon its surface. It often stains deeply with haema- 

 toxylin but after osmic fixation moderate extraction shows a 

 yellowish tinge. When saffranin and light green are used 

 the saffranin stained threads may be seen upon the surface of 

 the green plasmasome and after Auerbach's acid fuchsin and 

 methyl green mixture, the plasmasome is red, and chromosomes 

 green. During the later stages the threads become relaxed 

 from the plasmasome and it fragments, the parts becoming 

 spherical like drops of some non miscible fluid (fig. 15). 



4- The pro-phases. During the early prophases threads re- 

 appear and are paired, twisted and show a progressive massing 

 of the chromatin at paired loci upon the parallel threads as 

 they condense to form the chromosomes (fig. 15). The material 

 is not favorable for a detailed study of the formation of the 

 chromosomes; tetrads appear to form by a second cleft appear- 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 21, NO. 1 



