ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 29l 



Heredity and Variation.* — ^Y. K. Brooks points out that living 

 beings do not exhibit unity and diversity, but unity in diversity. 

 These are not two facts, but one. Inheritance or resemblance to 

 ancestors, and variation or difference from ancestors, are only imperfect 

 mental concepts — crude ideas, and not facts ; the fact is the indi- 

 viduality in kinship of living beings. But if resemblance to ancestors 

 does not exist in nature separated from individuality or difference 

 from ancestors, what becomes of the notion of a substance of inheri- 

 tance ? To- speak of such seems to Brooks a fallacy. The species is 

 no^ in chromatin, nor in germ-cells, nor in gemmules, nor in biophors, 

 nor in allelomorphs, nor in living beings : it is in that reciprocal inter- 

 action between the hving being and the natural world, of which it is a 

 part, which has been called the struggle for existence. The being of 

 the individual organism is not in itself, but in the reciprocal inter- 

 action between it and its environment. " Is it not time to have done, 

 once and for all, with the metaphysical, pre-Darwinian notion of species, 

 as something that resides in germ-cells, and is handed down by a sub- 

 stance of heredity ?" 



i>. Histolo&y. 



Origin of the Centrosome.t — J. Kunstler maintains that the 

 centrosome is the primitive cellular centre. It is due to a specialisation 

 of an ordinary plasmic spherule. " It seems to have preceded the 

 nucleus as an intracellular morphological element. Its role seems to 

 have remained essentially reproductive." Just as some cells have 

 several nuclei, so some have several centrosomes. 



Intercellular Connections of Epithelial Cells in the Intestine.^ — 

 R. Weigl finds clear evidence of intercellular bridges between epithelial 

 cells in the intestine of the newt, Proteus and Spelerpes. He finds that 

 the bridges contain prolongations of the endoplasm, and believes that 

 they may serve for the transmission of stimulus. 



Elastic Tissue.§ — Ed. Retterer has studied the elastic tissue in the 

 cervical ligament and in the aorta of the dog, cat, guinea-pig, and horse. 

 The origin of elastic structures is entirely cellular. The coalesced cells 

 have a homogeneous cytoplasm. In the cervical ligament the peripheral 

 cytoplasm forms elastic fibrils, and the number may be added to from 

 within at the expense of the clear cytoplasm around the nucleus. In the 

 aorta the cells that form the elastic fibres and lamellas are spindle-shaped 

 and disposed like epithelium. They have been described as smooth 

 muscle-cells. The peripheral cytoplasm is differentiated into elastic 

 fibrils disposed in zones or lamellas aiTanged concentrically around the 

 lumen of the vessel. As a cell is differentiated peripherally, the peri- 

 nuclear zone is reduced and the nucleus is much modified, gradually 

 showing the characters of elastin. The position of the cell-residues is 

 indicated Ijy clear spaces in the elastic lamellfe — the alleged pores of 

 fenestrated membranes. 



* Proc. Amer. Phil. Soc, xlv. (1906) pp. 70-6. 



t Comptes Rendus, cxliv. (1907) pp. 45-6. 



X Bull. Internat. Acad. Sci. Cracovie, 1906, pp. 777-91 (1 pi.). 



§ C.R. Soc. Biol. Paris, Ixii. (1907) pp. 56-8. 



