2 0. ISHTKAWA. 



verv little prc^topl-.i.^m. The chromatic elements are very much 

 elongated and appear as so many minute rods. Many of the cells are 

 in the state of division. 



In the growing zone (" Wachstlmmszone") the nuclei recede to 

 the state of rest, and the germ-cells grow to nearly double their size 

 after division in the first zone. 'I'his stage is, however, not so well 

 marked in this animal as in Ascaris ; we can nevertheless distinguish 

 it pretty easily by the absence in it of karyokinetic figures. 



And in the last zone we find again the active multiplicatit^n of 

 the cells. "Jede Zelle zerfallt jetzt durch zwei Theilungen, die sich 

 unmittelbar aneinander anschliessen, iri 4 Elemente, welche sich direct 

 zu den befruchtenden Samenkörpern umbilden. "^^^^ 



Fig. 1. represents a longitudinal section of a testicular sac not 

 very highly magnified, tlie lower end of the figure showing the blind 

 posterior end and the upper end the place wliere the vas deferens takes 

 its origin. The tln-ee zones here enumerated can be clearly seen 

 even bv this figure. The entire lower third of the sac represents the 

 formative zone in which are seen a few cells in division. The next 

 zone is well characterized by the peculiar appearance of the chromatic 

 elements and occupies the iniddle portic^n of the sac, while the last zone 

 or tlie zone of ripening is seen at the anterior end, well characterized 

 by the presence of many karyokinetic figures in it. 



a. The Formative Zone. — This zone occupies nearly one-third of 

 the entire testicular sac near its posterior end. The cells in this 

 part are found partly in the state of division and partly in the state 

 of the so-called " skein " stage (Kniiuelstadium), showing thus very 

 clearly that these are in active multiplication, as stated above 

 (fig. 1 k fig. 2). The chromatic elements of the nuclei in the 

 "skein" stage are found to be of \ery different thicknesses, owing 

 to tlie dilferent stages in which we observe them ; and their number 



