ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 335 



Development of Cross-striations in Heart Muscle of Chick 

 Embryo. — Margaeet Reed Lewis {Bull. Johns Hopkins Hospital, 

 1919, 30, 176-81, 1 pL). In the living cell cross-striations are present, 

 but uo fibrils. The cross-striations are very thin bands on the surface 

 of the cell. They extend across the cell and are never in the narrow 

 threads or fibrils. The fixation of the cell causes the formation of the 

 surface layer into fibrils in which the cross-striations are drawn together 

 into deeper bundles and thus become evident as sharply marked 

 structures. In places where the pull on the surface of the cell is such 

 that the latter is not coagulated into fibrils, the cross-striations remain 

 spread out as thin bands across the cell. The complete cross-striations 

 are present in the muscle of the heart of very young chick embryos 

 (10 myotomes), much earlier than was supposed by other observers. 

 The myofiljril theory is not satisfactory, at least in regard to heart 

 muscle, and this is not surprising. For the structure on which the 

 theory was based is not a part of the living heart-muscle cell, but only 

 of the dead cell. J. A. T. 



Ultra-microscopic Particles. — Albert and Mary Alexandre 

 {Introduction a la Biologie Micellaire, Paris, 1917, 38). Below the cell 

 are the micellae that compose it, ultra-microscopic spherical corpuscles. 

 The importance of the cell as a unit has been exaggerated. Syncytia are 

 common ; the germ-cells arise from cytogenous corpuscles {sic) ; there 

 are Protists without nuclei ; cells may disintegrate into micellae ; micro- 

 cocci are free and independent micellae ; crystals and minerals are built 

 up of petroblast micellae. There is no transformation, only aggregation 

 and disintegration. Nothing is born nor dies, all is assemblance and 

 dissociation. The most diverse beings are but transient associations of 

 ultra-microscopic beings, always fundamentally identical, which separate 

 and rejoin according to circumstances. Thus, we think, a fact is exag- 

 gerated into a fallacy. J. A. T. 



Enamel Org-an of Hake.— J. Thornton Carter {Quart. Journ. 

 Micr. Sci., 1918, 63, 387-400). In Gadidse, such as the hake 

 {Merluccius vulgaris), each tooth is surmounted by a pointed cap of 

 enamel which rests on a platform of dentine, whose central area extends 

 into the enamel cap, thus affording a firm support without increasing 

 the outside dimensions of the tooth over this area. The origin of the 

 tooth-germ is as in Mammals, there being an ingrowth of the deeper 

 layer of the oral epithelium and the growth of a dentine papillse which 

 becomes invested by the epithelium except at its base. The develop- 

 ment of the epithelial enamel organ is carefully traced. It consists, to 

 begin with, of two layers of cells, the one lying in apposition to the 

 dentine, consisting of columnar ameloblasts with well-defined cell out- 

 lines and the nuclei lying about the centres of the cells. Immediately 

 external, separating the ameloblasts from the surrounding connective 

 tissues, lies a layer of polygonal cells, usually two or three deep, consti- 

 tuting the external epithelium of the enamel organ. The ameloblasts 

 maintain their individuality throughout the whole period of the formation 

 of the enamel cap, and the fully developed enamel is the product of 



