156 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
exposure to difterent environments tlie very process producing the 
isolation brings together those of one kind, as 'svhen individuals of a 
special colour prefer to pair together. 
Degeneration of Ova.* — Prof. G. Kuge describes the degenerative 
processes in the egg-follicles of Vertebrates, especially in the unexpelled 
ovarian ova of Amphibians (^Siredon pisciformis and Salamandra 
maculosa). The death of the ovum is followed by changes in the 
surroundiug blood-vessels, and by a proliferation of the elements of 
the enveloping membranes. The dead ovum is penetrated by elements 
either belonging to the epithelium of the ejig-cell or to the blood. The 
invading cells loosen the yolk material which is then removed by the 
vessels. Finally, in the shrivelled ovum, there remains only the 
material which is not readily absorbed. The whole follicle has a 
certain unity, and is implicated in the degeneration of the egg-cell. 
Prof. Euge also gives a summary of similar processes observed by 
numerous investigators in fishes, reptiles, birds, and mammals. 
Professor Rabl’s Memoir on the Theory of the Mesoderm.-f — 
Dr. K. S. Bergh, under the title of “ Ein moderner Theoretiker und 
seine Methodik” has, as the title may lead us to suppose, a severe 
criticism on Prof. Kabl’s theory of the mesoderm. J 
j3. Histolog'y.§ 
Morphology and Physiology of Cell-nucleus. |1— Dr. E. Korschelt 
has investigated the nuclei of ovarian and of secreting cells. In dis- 
cussing the former he describes the change of form of the nuclei and 
their relations to their surroundings, taking as his chief text Dytiscus 
marginalise but also other Insects, as well as AnteAon and Simitlier. T'he 
change of position of the nuclei is described in various Insects and 
Coelenterates, and the structural changes of the nuclei of a number of 
forms are discussed. Under the same heads the nuclei of secreting cells 
are treated. 
His investigations had the object of showing that the cell-nucleus is 
not only active during the multiplication of cells, but that it also 
exhibits its influence on the cells during the performance of other 
functions. For example, the nuclei of ovarian cells send out processes 
towards the region in which the cell is taking up substance, and in 
secreting cells processes of the nuclei are directed to that part of the 
cell in which secretion is going on. From this we must conclude that 
the nucleus in one case affects the ingestive, and in the other the 
secreting activity of the cell. Moreover, the nucleus often loses its 
sharp boundary-line in such places, and its contents aj^pear to pass over 
into the cell-protoplasm ; this indicates an intimate relation between the 
substances of the cell and of the nucleus. 
The disappearance of the cell- boundary and the closer connection 
between nucleus and cell-substance effected thereby calls to mind the 
disappearance of the nuclear membrane in karyokinesis— a process 
* Morpliol. Jahrb., xv. (1889) pp. 491-554 (4 pis.). 
t Zool. Anzeig., xiii. (1890) pp. 17-24. % See this Journal, ante, p. 16. 
§ This section is limited to papers relating to Cells and Fibres 
11 Zool. Jahrb., iv. (1889) pp. 1-154 (6 pis,). 
