48 PROFESSOR VAN BENEDEM. 



scribed by Ray Lankester, from whom they have received the 

 name of " autoplasts^' (6). 



In that part of the intermediate layer which extends beyond 

 the blastodisc the nuclei form a single layer and are arranged 

 with very great regularity. But if the focus of the microscope 

 is so altered as to give an optical section of the egg, it is dis- 

 covered that in the median lens and also in the peripheral welt the 

 nuclei occur in various planes and that they appear to be dis- 

 seminated without order in the protoplasm of the intermediate 

 layer. 



The simultaneous apparition of a great number of nuclei, sur- 

 rounded each from the first with a granular radiated zone, in a 

 layer which up to that moment had presented no trace of nuclear 

 elements, can only be explained by admitting an endogenous 

 generation of cells in the protoplasm. The regular grouping of 

 the granules of the protoplasm around each of the nuclei as soon 

 as they make their appearance indicates a subdivision of the 

 protoplasm into so many cell-territories. It is not to be con- 

 cluded from the fact that we cannot distinguish the limits of the 

 cells, that there is no individualisation of the elements. The 

 radial striation of the protoplasm around the nuclei proves that 

 we have not here to do merely with a genesis of nuclei, but, 

 in fact, with a formation of cells ; nuclei and cell-bodies appear 

 simultaneously. 



I was unable to follow further the development of the eggs 

 whose history I had watched from the morning onwards j the 

 following morning most of them were dead. In others the 

 blastodisc, considerably extended, covered in a great part of the 

 deutoplasmic globe, and already exhibited the first traces of the 

 embryonic rudiments in the widened portion of the marginal 

 welt. A few hours later all my embryos had ceased to live, in 

 spite of the care which I had taken to renew the water frequently 

 in the course of the day. 



But a short time before this, I had been led to study a stage 

 of development very close to that which I have just described. 

 Figures 4 and 5 represent an egg in this stage, one seen in 

 optical section (fig. 4), the other seen from the surface (fig. 5). 

 The blastodisc, a little more flattened than in the previous stage, 

 is also more extended. It is in immediate contact throughout 

 its inferior surface with the intermediate layer. There exists no 

 trace whatever either of segmentation cavity or of germinal cavity 

 (Keitnhohle). 



The disc is formed of clear and nucleated polyhedric cells. 

 The only important character in which it difi'ers from the pre- 



