ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 945 



Raubers observations. After this indispensable historical summary, 

 Prof. Rauber communicates the result of his own researches : — (a) In 

 a section of Tropidonotus, exactly the same as that described by Merk, 

 Rauber notes the distinct presence of mitoses in ultra-ventricular 

 regions. In the two outermost mitoses, occurring in the outermost 

 layer of cells, the planes of division are horizontal ; in those further 

 inwards, approximately so. (b) The innermost mitoses emphatically 

 predominate, and the direction of division is generally radial, 

 occasionally somewhat oblique, and rarely tangential, (o) In the 

 brain of a young tadpole, proliferation occurs not only in the layer 

 next the cavity, but in all the other layers. The growth in thickness 

 is partly independent, through the multiplication and growth of the 

 original epithelium and by the formation of new layers by tangential 

 division, and partly secondary in consequence of superficial multipli- 

 cation of the epithelial layer by radial division, (d) In the spinal 

 cord of the tadpole, as in that of Tropidonotus, mitoses occur in the 

 outer, as well as in the inner strata. The increase in thickness is 

 therefore as in the brain, both direct, and indirect, (e) Similarly with 

 tho retina, the pre-eminently proliferating layer is the external, that 

 which originally bounded the primitive eye-ventricle, and is adjacent 

 to vhe subsequent pigment layer. Mitoses occur, however, in the other 

 layers ; the direction of division is pre-eminently, but not exclusively, 

 radial, and the growth in thickness is both direct and indirect. 

 (/) In the olfactory groove, the favourite proliferating layers are the 

 mesodermal, and those next to it. Mitoses occur, however, in all the 

 strata. A continuation relative to other Vertebrates is promised. 



Indirect division in Cells of Tumours.* — M. V. Cornil has 

 observed division by threes in the cells of two tumours, both of which 

 were epitheliomatous. Sections revealed the fact that the trilobate 

 chromatic filament became completely separated into three distinct 

 plates within one nucleus. 



Import of Cytozoa.f — Prof. J. Gaule has lately developed his theory 

 of the cytozoa which are regarded by most authorities as parasites in 

 the blood. He still adheres to the reasons which seem to him to 

 disprove the simply parasitic character of these elements. 



The typical cytozoa have a somewhat complicated structure. 

 They contain an unmistakable nucleus, and their protoplasm consists of 

 two portions, on the one hand of a substance occupying the two points 

 of the cytozoon (" nigrosinophilous substance "), and, on the other, of 

 two granules lying in a clear space at each side of tho nucleus (" eosin- 

 ophilous substance "). The cytozoon thus unites the nigrosinophiluus 

 substance characteristic of amoeboid cells of the (frog) blood, and 

 the eosiuophilous substance composing the granules of the plasma. 

 These two substances occur, indeed, variably in all cells. Almost every 

 kind of cell may form a cytozoon. The cytozoa vary considerably 

 within the same individual, and very greatly in different genera, 



* Comptes Renrlus, ciii. (1S86) pp. 78-80. 



t Biol. Centralbl., vi. (1880) pp. 315-51 (Beiicht Versamml. Deutsch, 

 Naturf. Strasaburg, 1885). 



Ser. 2.— Vol. VI. 3 g 



