1885.] new-york microscopical society. 163 



Amphipleura pellucida and the Diffraction Theory. 

 — The photographs of this diatom recently made by Dr. Van 

 Heurck have given rise to some discussion, and some of those 

 who do not admit the reality of the beaded appearance shown 

 by the photographs, claim to rest their view on the Abbe dif- 

 fraction theory. 



This shows that some misconception exists as to the applica- 

 tion of the theory, which does not establish, as supposed, that 

 all appearances of minute structure with high powers are wholly 

 illusory and do not correspond to any physical structure. On 

 the contrary, the images shown by the microscope are all, in fact, 

 caused by real structural peculiarities of the object observed. 

 Thus in the case of the " beads " of A. pellucida, the existence 

 of such an image proves that the diatom has not merely a peri- 

 odic differention of structure in orie direction, but that such 

 differentiation exists in two directions which cross at right angles. 



What the diffraction theory shows is that the real form and 

 structure of the beads cannot be determined by the mere inspec- 

 tion through the microscope of their images. The microscope 

 leaves wholly undecided the question whether they are eleva- 

 tions, or depressions, or simple centres of thickening in the sub- 

 stance of the valve, resulting, it may be, from the intersection of 

 two siliceous layers, the densities of which vary periodically. — 

 Jour. Roy. Mic. Soc, 1885, p. 529. 



" Omnis Nucleus e Nucleo." — It is nuclein that fertilizes. 

 Sperm-cell may unite with germ-cell, but there is no further 

 development unless the nuclei of the two cells combine. The 

 nucleus is regarded as a more highly organized substance than 

 protoplasm, and as representing a special centre of force in the 

 cell. — Dr. O. Hertwig. See Jour. Roy. Mic. Soc, 1885, pp. 

 421-423. 



Artificial Division of Infusoria. — Prof. M. Nussbaum 

 and, independently, Dr. A. Gruber have obtained some interest- 

 ing results as to the regeneration of unicellular organisms. The 

 former divided an Oxytricha into halves either longitudinally or 

 transversely and found that the two halves soon became normal 

 animals, and that the complete organisms thus formed developed 

 again by spontaneous division. If the artificial division be into 

 unequal parts, these parts grow again, except those which are 



