HISTOLOGY OF THE FROG 77 



fragment does not divide prior to the division of the cell- 

 body, so that the new daughter cells shall contain as many 

 nuclei as there were in the parent cell, but that a half of the 

 nuclei pass over to one cell, the other half to the other cell 

 formed by division. Moreover, the occurrence of truly multi- 

 nucleate leucocytes is much rarer than is commonly supposed ; 

 for, even where two or three nuclei seem to be present, close 

 inspection reveals the fact that they are united together by 

 strands of nuclear substance. In fact, the nucleus of the 

 leucocytes is rather irregular and lobate than .divided into 

 separate portions, and it is the irregular lobes folded over 

 one another which give the appearance of several nuclei. Such 

 irregular nuclei are in other respects similar to normal spherical 

 or sub-spherical nuclei ; they contain a network of the deep- 

 staining substance, chromatin, and in division behave as do 

 ordinary nuclei. 



But, as we shall see farther on, there are many unequivocal 

 instances of numerous independent nuclei being enclosed in 

 a single mass of protoplasm. Some authors regard these as 

 single cells, because the protoplasmic mass, the cell-body, is 

 single. Others hold an opposite opinion, and it is not an 

 easy matter to decide which of the two opinions is to be 

 preferred. But, as a matter of convenience, it is well to call 

 a single mass of protoplasm containing more than one nucleus 

 by a special name viz. ccenocyte. 



We have said that a cell consists of a mass of protoplasm 

 containing a nucleus. But this is not a satisfactory definition ; 

 for protoplasm is a vague general term which at the present 

 day has no very exact meaning attached to it. Protoplasm, 

 the material basis of life, was first discovered by Dujardin, who 

 called it sarcode. Dujardin stated precisely what he meant 

 by sarcode. "It is that," he said, "which other observers 

 have called a living jelly that gelatinous, diaphanous structure, 

 insoluble in water, which contracts into globular masses, 

 attaches itself to one's dissecting needles, and can be drawn out 

 in strings like mucus." Further than this, Dujardin recognised 

 that sarcode must be organised, must possess a structure. Not 

 that he was able, with the imperfect microscopes of the day, to 

 observe and describe a structure,, but he felt bound to postu- 

 late one, because of the vital activity of the substance. " Sar- 

 code is without visible organs, and without the appearance 



