ZOOLOCiY AND BOTANY^ MICROSCOPY, ETC. 729 



Division and Degeneration of Giant-cells of Medulla of Bone.* — 

 M. H. Demarbaix has investigated the history of myeloplaxos or giant- 

 cells of the medulla of bone. He finds tliat during life, and for a short 

 time after death, they consist of a vesicular nucleus, formed of a mem- 

 brane, achromatic filaments, chromatic bodies, and a fluid or enchylema. 

 Arnold's nuclei rich in chromatin do not exist during life ; they appear 

 a short time after death, and are the altered form of the nuclei seen 

 during life. The alteration commences with a swelling of the chromatic 

 bodies ; the colourable part soon forms, on the inner face of the nucleus, 

 a continuous layer, which thickens more and more, and ends by occupying 

 the whole cavity of the nucleus. This change is quite independent of 

 micro-organisms, and occurs some time before the similar alteration of 

 the small cells of the medulla. Degenerated nuclei oifer the same kind 

 of resistance to decolorizing agents as do nuclei in kinesis ; this appears 

 to indicate that the chromatin has undergone a modification by which it 

 becomes analogous to, if not identical with, the chromatin of karyokinetic 

 figures. The phenomena which Arnold has described under the name of 

 indirect division in the lymphatic cells of the medulla, the sjjleen, and 

 the lymphatic ganglia, are also post-mortem changes. 



Multiple kinetic division was normally observed in the myeloplaxes 

 of all the animals examined by the author, and must therefore be re- 

 garded as a physiolojT^ical process ; the statement of Coruil that there is 

 no binary division in the giant-cells is incorrect. Multiple kinetic 

 division is the only well-established mode of division, and the proofs of 

 direct division are cajDable of other interpretations, among which the 

 hypothesis of phagocytosis must be taken into consideration. 



In the normal state a certain number of cells present phenomena of 

 retrograde develojiment ; these are of two kinds ; in the first the nucleus 

 is converted into a drop of homogeneous semi-liquid substance, which 

 may further divide into a number of smaller drops, and these are some- 

 times expelled from the protoplasm ; in the second method the proto- 

 l)lasm disapjiears rapidly ; the colourable part of the nucleus forms on 

 its inner surface a refractive, continuous, and homogeneous layer. 



Comparative Study of Striated Muscle.!— Mr. W. A. Haswell comes 

 to the conclusion that there ax"e two principal types of striated muscle 

 in the Animal Kingdom — the simple and the compound — which are not 

 in any way genetically related to one another. Compound striated 

 muscular fibres are found in their most primitive, as well as in a more 

 highly developed, form in certain Polychaeta, where they occur as the 

 equivalents of bundles of simple non-striated fibres found in a cor- 

 responding situation in related forms. Each compound striated fibre is 

 derived from a bundle of simple non-striated fi.bres. In its simplest 

 form (in the pharynx of a species of Si/Uis') the comi^ound striated fibre 

 has only a single transverse network running through a zone of singly 

 refracting substance situated at about tl;e middle of the fibre, with two 

 doubly refracting zones, one on either side of it. In a slightly higher 

 stage two other transverse networks nre added, one on either sicle of the 

 middle one ; in other species of Si/llis the fibres present from half-a- 

 dozen to twenty transvt-rse networks. In Syllis coruscans, the species 

 in which the fibres are most highly developed, they have all the essential 



* La Cellule, v. (1889) pp. 27-57 (2 pis.)- 



t Quart. Joura. IMior. Sci., xxx. (1889) pp. 31-50 (2 pis.). 



