1036 



development takes place by means of the activity of the ependyma 

 and to a subordinate and limited extent by means of direct division. 

 Where (hese elements exist they sink down and gradually disappear, 

 sending off a first process, which grows and is lengthened, while 

 others are also developed, so thai gradually a multipolar cell arises. 

 "Avant d'arriver a cette diflferenciatiou, ces elements se divisent ca 

 et la par scission directe, qui, on bien se complete — et alors les 

 nouveaux elements restent en connexion avec un des prolongements 

 — on bien ne s'achève pas, et on a alors des formations gemellaires 

 de divers degré. Ces faits penvent s'observer le long de la moelle 

 épinière d'individus d'age différent et dans des preparations obtenues 

 avec des séries de sections frontales et avec las divers colorations". 

 Palauino accompanies his statement with a figure to show how the 

 epithelium-cells (ependyma) are further differentiated and move down 

 into the surrounding tissue. On the other hand it is to be regretted 

 that P. did not add a figure showing a cell engaged in direct division 

 and that he did not give a more detailed description of the amitoses 

 in the central nervous system observed by him. 



The more thoroughly I study my preparations from the central 

 nervous system of animals of various post-embryonic ages, tlie more 

 convinced am I that Paladino is right in his statements as given 

 above. In these preparations of mine I have found, in a number 

 of places, appearances that indicate, just as clearly as P.'s figure, a 

 movement of cells from the ependyma into the surrounding tissue. These 

 appearances are not, however, found continuously along the whole 

 central canal, but occur scattered here and there — this too agrees with 

 P.'s statements. On the other hand, with regard to figures of direct 

 cell division, I have observed a great many which, in my opinion, 

 are to be interpreted in this way. And as a matter of fact I have 

 obtained series of such appearances which show the different stages 

 of a direct cell division. Notches, indentations and irregularities in 

 shape occur very often in the nuclei of the nerve cells. If, howexer, 

 such appearances be examined more closely, we shall find in most 

 cases that they cannot be counted as figures of amitotic divisions- 

 Thus figures which may with a great degree of probability be 

 considered as stages of amitotic cell divisions do not occur in such 

 abundance in my preparations of the spinal cord from the above- 

 mentioned animals. Fig. 13 shows a type of these notches, whicii 

 are very common in the nuclei of ganglion-cells, but which, as far 

 as one can see, have nothing at all to do with amitotic divisions 

 of the cells. Figs. 14 and 15 are cell-plasmodia or syncytia, of which 

 one often sees examples, especially close to the ependyma. The 



