A Cytological Study of the Semi-parasitic Copepod, Hersilia apodifonnis etc. 411 



forms the "nuclear cap"i), imlike mitochondria, is seemingly repelled 

 by the orieiiting force, for the cyto-plasmosomes never unite in the 

 vicinity of the positive pole. The niicleohis resulting from the fiision 

 of the two nucleoh also shows repulsion and lies opposite the positive 

 pole (Figs. 14, 15, Plate V). 



The changes taking place in the chroniatie substance in the foUowing 

 stage are the most marked and undoubtedly the most rapid of any in the 

 growth of the germ cells (Figs. 12 /, /', 14—16). The first thing to 

 attract attention in such a nucleus is the loss of the orderly polar arrange- 

 ment of the threads; and, secondly, we see three kinds of threads — 

 thick threads double along their entire length, thin threads siniilar to 

 those of the leptotene bouquet, and threads douljle along part of their 

 length, then spreading out into two thin branches in the form of a Y 

 or a T. The fact that in the only transitional stage between the lepto- 

 tene bouquet (Fig. 12 e) and the zygotene bouquet (Figs. 12 g, 17), one 

 finds Single threads, double threads, and threads partly united in the 

 same nucleus argues for a side by side pairing of the leptotene threads. 

 Neither a gradual thickening of the leptotene threads, nor any indica- 

 tion of a broadening and Splitting of the granules composing them could 

 be found. The entire evidence pointed toward a doubling through para- 

 syndesis. 



That such cells, as shown in Figures 12 /, /', 14 and 15, are transi- 

 tional stages in the union of the leptotene threads into double chromatin 

 bands of half the number is upheld by a comparison with optical sections 

 viewed from the positive pole, as Figures 13, 16, and 18. (Compare 

 lateral view, Figures 12 e, 14, and 17.) In the leptotene bouquet be- 

 tween forty-five and fifty ends were counted. Figure 18 represents a 

 similar optical section of the zygote ne bouquet, which is also characterized 

 by an orderly polar arrangement of the threads. Gross sections of these 

 threads show two deeply staining centers, and the result of couuts in 

 such nuclei varied from twenty to twenty-five, indicating that half 

 as niany loops are present as in the leptotene bouquet. If we now ex- 

 aniine a cell in the transitional period (Fig. 16), we find that the disturb- 

 ance of the polar orientation of the loops makes counting much niore 

 difficult — lengths of either Single or double threads being always in- 



1) Steuer ('03), in a study of Myiilicola, describes a disk-like body in the growth 

 of the spermatocytes, wliich he calls the "Idiozom" or -'Centrotheca". This body stains 

 deeply in iron-hämatoxylin ; but, if strongly decolorized, shows two centrioles within. 

 Whether or not this "Idiozom" is homologous to the "nuclear cap'- in Hersilia, cannot 

 be decided from Steüer's fig-iues. 



