ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
593 
species are very difficult to distinguish from one another. The com- 
parison of poecilogonic and convergent forms explains to a certain point 
the differences which exist in the crossing of various wild species, and 
which have offered so much difficulty to the philosophers. 
When etnbryological condensation is carried very far it gives rise to 
progenesis, which still further complicates poecilogouy, as in the Axolotl 
or in Chun’s examples of Ctenophora. Finally, obligatory parthenogenesis, 
which the author has shown to be. the result of the condensation of de- 
velopment carried as far as the early phenomena of oogenesis, may be 
added to poecilogony ; examples are found (as “ heterogony ”) among 
Trematodes, Aphides, and others. 
B. Histology. 
The Animal Cell.* — Prof. J. Chatin, well known for his useful and 
easily read accounts of scientific subjects, has published a small volume 
on the structure and life of the animal cell, in which the various biolo- 
gical phenomena are successively dealt with. The concluding chapter 
gives some hints on the way in which the cell should be studied. 
Attraction Spheres and Central Bodies. f — Dr. 0. Burger attempts 
to interpret these structures. E. van Beneden believes that the attrac- 
tion sphere with its central corpuscle is a permanent organ of the cell, 
“ au meme titre quo le noyau lui-meme.” Boveri also describes the 
centrosoma as a distinct structure. Recent investigations have proved 
the occurrence of attraction spheres and centrosomata in many different 
kinds of cells, both of plants and animals. But what do these structures 
mean ? According to Burger the sphere and its centre is not an organ of 
the cell, but rather a phenomenon due to mechanical processes occurring 
within the plasma. The centre is a ball of protoplasm around which 
the microsomata are arranged in a concentric sheath ; the centre is not 
the cause, but the result of the attraction of microsomata. That the 
central corpuscle can be differentiated by staining from the rest of the 
plasma may be merely an expression of its concentrated composition. 
Herr Burger answers various objections which may be brought against 
his interpretations, and advances counter-objections against van Beneden’s 
view. 
Relation of Nucleus to Cell-substance during Mitosis.];— Dr. H. F. 
Muller has investigated in this connection the haemoglobin-containing 
blood-cells of the spleen in Triton and similar cells in Mammals. After 
the disruption of the nuclear membrane during metamorphosis sub- 
stances of the cell-plasma do as such pass into the nucleus. Herr 
Muller regards this mingling of paraplasma and nuclear sap as of 
essential importance in the process of indirect division. 
7. General. 
Influence of Fresh Water on Marine Animals.§ — Don Jose Gogorza 
y Gonzalez has studied in a more exhaustive manner than has hitherto 
been done the influence of fresh water on marine animals. After an 
* ‘La Cellule Animale,’ Paris, 1892, 8vo, vi. and 304 pp., 149 figs, 
t Anat. Anzeig., vii. (1892) pp. 222-31. 
t SB. K. Akad. Wiss. Wien, e. (1891) pp. 179-88 (1 pi.). 
§ Anales Soc. Espari. Nat. Hist., xx. (1891) pp. 221-70 (1 pi.). 
1892. 2 s 
