552 SUMMARY OF CURRENT RESEARCHES RELATING TO 



it, just ns much as in freely living animals, the firm suhstance increases 

 considerably at the expense of the watery ; the inorganic constituents 

 take but a very small share in this increase. At the beginning of tleve- 

 lopmeut there arc formed tissues which are very ricli in water, and this 

 richness of water steadily diminishes as development goes on. The 

 substances soluble in water are so disposed that their absolute quantity 

 increases with increasing development, while their relative quantity (as 

 compared with the other constituents) diminishes. It is just the reverse 

 with tlie constituents which are soluble in alcohol. The fatty matters 

 undergo considerable increase. The quantity of albumens and albu- 

 minoids which are insoluble in water absolutely increases as develop- 

 ment goes on, but relatively the quantity remains almost unchanged. 



Among other points dealt with by the author are the presence of 

 mucin, the quantity of haemoglobin, and the composition of the embryonic 

 feathers and of bone as compared with those of older forms. 



B. Histologry.* 



Cell-Studies. t — Herr T. Boveri believes that the course of karyo- 

 kinetic division may be generally described in the following terms : — 

 The chromatic nuclear material becomes collected together into a definite 

 number of isolated pieces of a form characteristic of the kind of cell — the 

 chromatic elements ; an achromatic filamentar figure is formed into two 

 poles, either from the substance of the nucleus or from that of the cell. 

 The chromatic elements, so far as their number, form, and size allow 

 it, are deposited in the equatorial jilane of the achromatic figure ; the 

 chromatic elements divide into two halves, one of which makes its way 

 towards either pole ; the daughter elements break up in the framework 

 of the new nuclei. 



In the ova of Ascaris lumbricoid.es the germinal vesicle has, in the 

 earliest stage, the typical structure of the resting nucleus, and we are 

 justified in supposing that the chromatic elements arise from the frame- 

 work in exactly the same way as in other cases, though the details cannot 

 be certainly made out in consequence of the small size of the object. 

 The arrangement of the elements in an equatorial plate, their transverse 

 division, and the formation of daughter-jilates are eftected in just the 

 same way as they are now known to be in other cases, and especially 

 in the ova of Arthropods. The only point of difference is the relation 

 of the daughter-elements which remain in the egg after the expulsion of 

 the first polar globule, for these remain isolated, and so are the direct 

 mother-elements of the next spindle. 



In the germinal vesicle of the ovum of Ascaris megalocephala (Carney's 

 type) two indeijendent portions of chromatin are found in the earliest 

 known stage ; though nothing is certainly known of their mode of 

 formation, it may be assumed that they are derived from a typical 

 nuclear framework. This conversion, however, of the reticulum into 

 the chromatic elements, which in other cells and in some ova {A. lumhri- 

 coides) directly precedes division, appears in most eggs to take a long 

 time. The important difference in the eggs of the type of Van Beneden 

 is that there is but one chromatic element ; this seems to be unique. 



There are many reasons for supposing that the division of the chro- 



* This section is limited to papers relating to Cells and Fibres. 

 t Jenaisch. Zeitschr. f. Naturwiss., xxi. (1887) pp. 423-515 (4 pis.). 



