NiO: 2.i] YOLK-NUCLEUS AND POLAR RINGS. LT 
shade of blue from that at the poles. It shows (though in a 
less degree) the blending of the red and blue described under 
Fig. 8. 
In a somewhat later stage (Fig. 13) the membrane of the 
pronuclei is entirely gone, the chromatin is in the form of 
loops, and the archoplasm is present around the loops and in 
the cytoplasm. 
Fig. 14 represents one of the polar rings before staining 
with Lyon’s blue. The egg was killed in Hermann’s fluid, 
and the section was stained for twenty-four hours in lithium 
carmine. We see here how (in Hermann’s preparations) 
lithium carmine stains the cytoplasm, and does not stain the 
polar ring substance. This section also represents the black 
spots referred to above (Deutoplasm), which subsequently were 
completely dissolved away by soaking the sections for twenty- 
four hours in warm xylol. 
In studying the literature on the so-called yolk-nucleus I 
have found that in many cases the substance follows more or 
less closely a course of development similar to that of the 
polar ring substance of this egg. It appears first close to the 
germinal vesicle, increases in amount as the egg grows, and in 
some forms becomes distributed in granular masses near the 
periphery of the egg, while in others it appears as numerous 
clumps or granules throughout the cytoplasm. In many cases 
the figures show aggregations of the substance which strongly 
suggest polar rings. I shall, however, quote only those cases 
where the author specifically states that the substance is finally 
aggregated at one or both poles of the egg.! 
Stuhlmann’s? results from investigations of a variety of 
insects furnish the strongest evidence that the Dotterkern of 
these animals and the polar rings of Al/olobophora foetida are 
1 For the latest historical sketches of the ‘“ yolk-nucleus,” and for the literature 
on the subject, see L. F. Henneguy, “ Le corps vitellin de Balbiani dans l’oeuf des 
vertébrés,” Journ. de lanat. et de la physiol., ann. 29, 93; and H. Mertens, 
“Recherches sur la signification du corps vitellin de Balbiani dans l’ovule des 
mammiféres et des oiseaux,” Archives de Biologie, tome XIII, 1893. 
2 Franz Stuhlmann, “ Die Reifung des Arthropodeneies nach Beobachtungen 
an Insekten, Spinnen, Myriopoden und Peripatus.” Ser. d. naturf. Ges. z. Freiburg. 
i. Br., Bd. I. 1886. 
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