RESEARCHES ON KARYOKINESIS AND CELL DIVISION. 39 



was unstained and consisted of achroraatin ; the finei* net- 

 work is not to be seen in living cells. Flemming studied it 

 in well-stained preparations from the Salamander. He also 

 discovered that the " nuclear membrane " was composed of 

 minute flat plates of chromatic substance in connection with 

 the fibrils of tlie chromatic netAvork; these plates were 

 separated from each other by slight intervals, so that the 

 membrane seemed to be pierced with holes like a sieve, but 

 he was unable to decide whether the intervals between the 

 plates were really apertures or occupied by achromatic 

 substance. None of Flemming's new observations give any 

 support to Klein's statement that the intranuclear and 

 extranuciear networks are continuous one with the other. 



Filler Structure of the Nuclear Network. — In a paper 

 which has recently appeared. Dr. W. Pfitzner (ref. 'Morph. 

 Jahrbuch,' vol. vii) of the Anatomical Institute at Heidel- 

 berg, states definitely what is brought forward as an 

 opinion by Flemming, viz. : that the chromatin and achro- 

 matiu are distinct in the resting nucleus, but he makes 

 no mention of a finer as contrasted with a coarser net- 

 work. The preparations in which he determined this point 

 were sections of the epidermis of the larva of Salamandra 

 treated with a 1 per cent, solution of gold-chloride, either 

 examined without further treatment or after exposure to 

 light in a 5 per cent, solution of formic acid. In sections 

 thus prepared the meshes of the network were not stained. 

 Dr. Phtzner also declares that the nucleoli in the resting 

 nucleus are never connected with the network, but lie 

 free in its meshes, and that there is no " nuclear mem- 

 brane." The appearance which has been interpreted as due 

 to a membrane is caused by the contrast in optical proper- 

 ties between the achromatin and the surrounding cell proto- 

 plasm ; he argues that if a membrane were present it would 

 appear, on focussing the surface of the nucleus, as a flat 

 expansion, whereas in reality a network is seen in all optical 

 sections. These are points treated incidentally in this paper, 

 the object of which is to make known certain discoveries 

 in the structure of tVie chromatic fibrils made by means of 

 a -V homogeneous immersion system by Seibert and Kraft. 

 Certain of these fibrils appeared to be composed of a series 

 of granules ; and Dr. Pfitzner has come to the conclusion 

 that the chromatic fibril is not homogeneous in structure, 

 but always consists of a moniliform succession of minute 

 spherules of chromatin, held together by an unstained sub- 

 stance which is probably achromatin. He first observed 

 fibrils of this structure in ordinary preparations of the epi- 



