p2 C. M. CHILD. 



no visible characteristic stages of preparation and reconstruction 

 and no clearly visible chromosomes and spindles. The dividing 

 nucleus usually does not stain differently from any other, and 

 after division there is in many cases no demonstrative evidence 

 that the nuclei have arisen by division. Certain critical stages in 

 the division must be found, viz., those in which separation is just 

 beginning and the two parts are manifestly connected. More- 

 over, such stages must be found frequently in order to establish 

 the presumption that anything more than an abnormal or perhaps 

 a degenerative process is involved. My observations have ful- 

 filled these conditions. Thousands of cases of the critical stages 

 have been observed. Cases more or less similar to every case 

 figured in the drawings have been observed repeatedly. As re- 

 gards a possible failure to recognize mitoses when they occur it 

 should perhaps be said that perfectly distinct and characteristic 

 mitoses do occur at certain times and places and that there is no 

 chance for confusion of these with anything else : chromosomes, 

 spindle, centrosome, equatorial plate, division of the chromo- 

 somes, etc., all are visible and instantly recognizable. In fact it 

 has been possible in the germ cells of one species to establish 

 the number of chromosomes with a considerable degree of ac- 

 curacy. It is very certain that the form of division which I 

 have designated amitosis in these species cannot be interpreted as 

 mitosis indistinctly visible or of peculiar form. All drawings are 

 made from camera drawings and schematization of the actual 

 cases of division and "improvement" of the camera-drawings 

 have been avoided as far as possible. 



Many of the figures are schematic in that non-essentials are 

 omitted and simple methods of representation are employed, but 

 every case of amitosis figured is as nearly like the observed case 

 as it was possible to make it after the most careful examination. 

 No attempt has been made to represent the parenchymal sub- 

 stance in which the cells lie in the earlier stages of development, 

 and when, as is often the case, no well-marked area of cytoplasm 

 appears about the nucleus, no cell-boundaries are indicated and 

 the nucleus alone is drawn. As a matter of fact the distinction 

 between cytoplasm and parenchymal substance, at least during 

 the earlier stages, is not nearly as sharp as the figures indicate, for 



