blackman: the spekmatogenesis of scolopendua. 81 



In Protozoa (Calkins, :01, p. 253) " Five types of nuclei, based upon 

 the disposition of the chromatin, can be distinguished. Of these the 

 most primitive is, (1) the solid sphere, or karyosome (Binnenkorper, 

 Rhumbler), which has neither linin reticulum nor membrane (e. g. 

 Calcituba). An advance is shown in (2) nuclei having one such kary- 

 osome surrounded by karyolymph, the whole enclosed within a mem- 

 brane (vesicular nuclei, Gruber, '84) ; while still higher types are (3) 

 nuclei with several karyosomes (two to thirteen or fourteen), with mem- 

 brane, karyolymph, and with or without a nuclear reticulum (e. g. Xocti- 

 lucd) ; (I) nuclei with a large number of smaller masses of chromatin 

 enclosed in a definite membrane with or without a linin reticulum 

 (e. g. Amoeba proteus) ; (5) nuclei consisting of granules of chromatin 

 unconfined by a nuclear membrane and spread over the entire cell (dis- 

 tributed nucleus) or aggregated about a central body (" intermediate " 

 type of Calkins, '98, e. g. Tetramitus)." 



Thus the more simple nuclei, the first type, are but single homo- 

 geneous masses of chromatin, i. e. karyosomes. Those of the second 

 type show some advance. They contain achromatin as well as chro- 

 matin and are surrounded by a definite membrane. " The chief 

 interest (p. 254) of these nuclei, however, centres in the chromatin 

 mass, the 'karyosome' of Labbe ('96), which, as in similar nuclei 

 among the Sarcodina, has been described under several names." It 

 often appears homogeneous, but is not really so. " The cortical portion 

 consists of chromatin with an exceedingly fine alveolar structure." The 

 history of this karyosome is strikingly similar to that of the isolated 

 chromatin mass in Calcituba (1st type). A higher kind of this type is 

 that found in Actinosphaerium (Hertwig, '99). In this genus "the kary- 

 osome in nuclei of ordinary vegetative forms is distinctly granular, the 

 chromatin granules being grouped in a variety of ways." Hertwig says : 

 " Das Kernnetz . . . enthalt sicher kein Chromatin. . . . Ich muss an der 

 friiher von mir gegebenen Schildernng fest halten, das alles Chromatin 

 in dem grossen Korper abgelagert ist den ich friiher ' Nucleolus ' genannt 

 habe." This " Chromatinkorper " is usually colored deeply by the 

 chromatin stains, and in the majority of cases seems to be of a granular 

 consistency, although at times it appears homogeneous. In many of 

 Hertwig's figures ('99, Taf. IT. Fig. 8, 10, et al.) it is strikingly like the 

 karyosphere of Scolopendra in appearance, while in others it differs 

 considerably. The "Chromatinkorper" consists of two substances, 

 "(l)das Chromatin, (2) das Material, welches die achtcr chromatin- 



freien Nucleoli der Gewebszellen bildet, fur welches Carnoy ('98) und 



6 



