50 THE GERM-PLASM 



for it is well known that the affinity of the chromosomes for 

 colouring matter varies markedly at dififerent periods, and this 

 indicates that slight changes, which are beyond our control, take 

 place in the constitution of this substance, and are sufficient 

 to cause its most striking reaction with regard to colouring 

 matters to disappear for a time. Chemical analysis of the 

 substance contained in the nucleus has certainly established 

 the presence of ' nuclein ' ; but although it is probable from 

 Mieschers * excellent observations on the sperm of the salmon 

 that nuclein is derived from the nuclei of the sperm-cells, it is 

 not by any means certain from what part of the nucleus it 

 originates : if one supposes that over 48 per cent, of the dried 

 sperm consists of nuclein, it is doubtful whether this is contained 

 in the small mass of chromatin which we see in the form of 

 chromosomes. 



Another recent observation may be mentioned here, which 

 proves at any rate that matter is actually transferred from the 

 chromosomes of the nucleus into the cell-body just at the time 

 when the characteristic structure of the cell-body is being 

 formed. I refer to Rtickert's observations on the remarkable 

 alteration in the size of the chromosomes of the nucleus during 

 the growth of the ovum of the dog-fish. f One of the youngest 

 ova observed in the ovary — which measured 2 mm. in diameter 

 — contained from 30 to 36 chromosomes, each of which was 

 12 microns J long, and 2 cubic microns in bulk: later on, in 

 nearly ripe eggs, the length of a chromosome reaches 100 /x, 

 and its cubic contents 7,850 cubic /a, or more accurately, since 

 it has meanwhile become doubled by division, 15,700 cubic /x. 

 Still later, just before the formation of the first polar body, 

 when the ovum is ripe and has attained its full size, the length 

 of the individual chromosome diminishes to 2 /x, and the cubic 

 contents of a double rod to 3 cubic /x. Ruckert infers from 

 these facts that the chromosomes give ofi" a great amount of 

 substance to the ovum during the gradual ripening of the latter, 

 and we can only agree with him on this point. But the ques- 

 tion arises as to how this transference of substance takes place, — 



* Miescher-Riisch, ' Statist, u. biolog. Beitrage zur Kentniss vom Leben 

 des Rheinsalm,' 1880; Schweiz. Literatursamml. z. internationalen Fisch- 

 ereianstell. in Berlin. 



t J. Ruckert, ' Anat. Anzeiger,' loth March, 1892. 



X A micron (m) is the ijj'on of a millimetre. 



