15 



united bj fine threads, and the niicleolns. T iievei* saw a resting 

 nucleus witli two nucleoli. There is nothing special to say about tlie 

 nuclear membrane and the nuclear network. With regard to the 

 latter there is here as little reason as in other cases for assuming 

 that the granules and the connecting threads are chemical Ij dilTerent. 



The nucleolus calls for special attention. Superficial observation 

 would lead to the assumption that it is an almost spherical body, 

 about which nothing special can be said. More exact observation, 

 even before the action of chromic acid, shows that sometimes two 

 small points on the nucleolus can be disiinguislicd. During t!ie action 

 of chromic acid Ihey become much more visible and are seen to l)e 

 small bodies which sometimes resemble rodiets. They are situated 

 on the periphery of the nucleolus, usually opposite one another and 

 seem often half immersed in the principal mass. According as a 

 more concentrated or weaker solution of chromic acid is used, the 

 nuclear network or the main mass of the nucleolus dissolves first. 

 In either case, however, the two small bodies show a longer resis- 

 tance. During the process of dissolution it can be seen that the two 

 small bodies are united by a thread which generally runs across 

 the nucleolus and is straight or slightly l»ent, but which may also 

 be much curved. When the nuclear network has dissolved and the 

 chromic acid has also had a strong solvent action on the main 

 mass of the nucleolus, the thread which unites the two small bodies 

 can be distinguished, and when the preparations are further stained 

 with "Brilliantblau extra griinlich", all is still more clearly and 

 more easily visible. The two corpuscles are stained dark-blue, the 

 thread, which unites them, is paler and the rest of the nucleolus is 

 light blue. After more prolonged action of the chromic acid the 

 threa^i with the two corpuscles alone is still present; after a still 

 longer action only the' latter are found and finally these also are 

 seen to have dissolved. This can all be seen with special clearness 

 after staining with "Brilliantblau extra griinlich." 



In every [ireparation that I made, the above observations were con- 

 firmed dozens of times, so that I am in no doubt that the nucleolus 

 in Zt/ipiema diffei-s in type from that of the higher plants, and resembles 

 the nucleolus of Spii'ogyra in having a [)eculiar structure. In 

 Spirogijra there are two convoluted threads or a threadwork or 

 network, in Zi/qnema cniciatum there are two short corpuscles 

 united by a thread oi- indeed a thread with two thickened ends. 



I consider the main mass of the nucleolus in Zygncma as identical 

 with the substance which occurs in Spirogijra together with the 

 threads or the thread- or network in the Jiucleolus. I have not been 



