A Cytological Study of the Semi-parasitic Copepod, Hersilia apodiformis etc. 417 



plasmosomes (cpl, Fig. 45) to form a large "nuclear cap" (n.c.,Figs. 46, 

 47), and the fusion of the nucleoli {^ill, Fig. 45) to one of greater size 

 (nlL, Fig. 46). Followiiig the boiiquet stage (Fig. 47), in which the 

 doubleness of the threads is very apparent, come the stages which are 

 not present in the spermatocytes. First there is a more orderly arrange- 

 ment of the loops toward the positive pole, together with a narro-^ing 

 of the chromatin bands, and the disappearance of their light longitudinal 

 line, or conjugation plane. This is the beginning of the long period of 

 growth in the oöcyte. The chromosomes gradually lose their compactness 

 and staining power, forming indistinct, flocculent areas; the nucleolus 

 increasesin size; and the "nuclear cap" breaksup into cyto-plasmosomes 

 which are very conspicnously seen against the nuclear membrane (shown 

 on a small scale, Fig. 3, Plate IV). The chromosomes are not again 

 visible until the oöcyte has completed its growth, then they come into 

 view as strepsistene threads, such as figured by Krüger ('11) iov Ccmtho- 

 camptus (his V\gs. '6 a—h, Taf. VII). In Hersilia, the chromioles are so 

 large and the connections between them so inconspicuous that they look 

 like chains of beads. The strepsistene threads contract to form double 

 rods (Fig. 48, Plate VI), which often show an angular bend at the 

 middle (the upper pair, Fig. 48) and always have granules between them 

 which stain more deeply than the chromatin itself in iron-haematoxylin. 

 The exact nature of this substance is not at aU clear ; but it is probably 

 the same substance that exists between the components of the tetrads 

 of the metaphase plate, as can be demonstrated by staining Flemming 

 material with crystal violet and alizarin, and then decolorizing until the 

 chromosomes retain only the alizarin. A band which stains a deep violet 

 can then be seen between the chromosomes, and the points of attach- 

 ment of the spincUe fibers have the same color (Fig. 51, Plate VI). 



The stages following that shown in Figure 48, — namely, the f urther 

 condensation of the chromosomes, the disappearance of the germinal 

 vesicle, and the formation of the spindle — are hidden by the deep 

 stainability of the entire region in which they take place. This phenom- 

 enon has been described by j\L\tscheck ('10, p. 78) for Diaptomus. 

 In the equatorial plate (Fig. 49) are twelve chromosomes, eleven with a 

 "Querkerbe", which in several cases is nearer to one end, and one 

 chromosome (s.) without a "Querkerbe". Seen in lateral view (Fig. 50, 

 Plate VI), the chromosomes are in the form either of rings or of 

 parallel rods. At the right in Figure 50 is a ditetrad comparable to that 

 shown in Textfigure Eö, in which the "Querkerbe" does not divido the 

 chromosome into two equal segments. 



27'^ 



