MUSEUM OF COMPARATIVE ZOOLOGY. 257 



FrommaN]^ ('65 and '67) was the first, according to Flemming ('78^, pp. 350, 

 351), to demonstrate on fresh objects, in addition to such as had been hardened, 

 the existence of branching filaments within the nucleus. Frommann does not, 

 however, seem to have directly stated that these filaments by anastomosing 

 completed a genuine network. I have not been abl^ to consult the original 

 papers by Frommann. 



CouRVOisiER ('6,6, pp. 24, 25) fijids in nerve cells of the sympathetic system 

 that " there emerge from the nucleolus, from the innermost centre of the cell, 

 fibres which are in part coarse and in part almost invisibly fine. These are 

 most easily recognized in clear nuclei, which they traverse in a radial direction, 

 and thus adorn with a star-like figure." They are the " Wurzelfaden" of 

 Courvoisier. 



It should be added in this connection, that subsequently Courvoisier ('68, p. 

 134) "could not establish with certainty stellar figures in the nucleus — pro- 

 cesses of the nucleolus" — in the case of the frog. Compare also pp. 142, 143 

 of the last-mentioned paper. 



ScHWALBE ('68, p. 60) has often observed a radial arrangement of the sub- 

 stance of the nucleus [ganglionic cells] with the nucleolus as centre. The 

 granules of the latter, however, do not afi'ord confirmation of Frommann's view, 

 which would make them to be the optical sections of nucleolar fibres. Vacuoles, 

 although occurring in nerve cells of Arion {loc. ciL, Fig. 15), are not to be found 

 in those of the vertebrates studied by Schwalbe (p. 63). 



Arndt ('68, pp. 473-492) recognizes no less than four kinds of " nucleolar 

 filaments " in the cells of the cerebrum, but all are, in his opinion, to be other- 

 wise explained than as structural filaments which traverse the substance of the 

 nucleus. Either they are the optical expression of fissures in the nuclear sub- 

 stance, or really lie outside the nucleus, or are due to phenomena of refraction 

 (p. 476). 



After his discovery of a hollow sphere of granules surrounding at some dis- 

 tance the nucleolus in cells from the skin of the mole's muzzle,* Eimer ('72) 

 extended his observations on the structure of the nucleus, and came to the con- 

 clusion that this '* Kornchenkreis " was a very general feature of nuclei in the 

 full vigor of life. 



The clear area which Eimer described in the first-mentioned paper as im- 

 mediately surrounding the nucleolus, he finds almost always present. That 

 portion of the nucleus, however, which lies outside this " clear area," and from 

 which it is separated by the " circle of granules," is not always dark, as reported 

 in his first article, but may present the same appearance as the " clear area." 



In his paper on the eggs of reptiles Eimer ('72«, p. 236) finds further con- 

 firmation of this peculiarity of the nucleus in the follicular epithelium. He 

 also gives figures of the division of the nucleolus (Taf. XII. Fig. 26. a) which 

 strikingly recall certain phases of the process of division in the nucleus as at 

 present understood. 



In studies on nerve cells of the sympathetic system, and on the skin of Sala- 



* Eimer, '71, p. 189, Taf. XVII. Fig. 8. 

 VOL. VI. — NO. 12. 17 



