The Micros(;opk. 295 



clers, mjanapods, crustaceans, etc. Before Carnoy, tliis class 

 of animals had never been studied with reference to cell-division, 

 and what led him to choose this group, he tells on his first page. 

 " Large cells," he says, " of a remarkable beauty, and of an 

 incomparable perfection, young and without inclavata, with 

 gigantic nuclei, even sometimes visible to the naked eye, . . . 

 with membranes that rival those of plant cells — this alone would 

 be sufficient to fix the attention of an}^ cytologist. . . . The 

 Arthropods alone are suflicient to write cellular anatomy." 



There are many, even among our best microscopists, who 

 imagine that the study of cytology is unapproachable to any one 

 but the professionals. Let the reader be convinced at once that 

 this is a false impression, and the sooner it is dispelled from the 

 minds of amateurs, the better it will be for science. 



There are two kinds of cell-division. The first is by simple 

 fission or constri:jtion of the nucleus and protoplasm ; this has 

 been called, by Flemming, direct division ; Carnoy proposes the 

 term, akinetic-division, or simple stenosis. In this mode, there 

 are no apparent movements in the nucleus or protoplasm, and it 

 may take place by simple constriction or by means of a cell, 

 plate, similar to that observed in plants. Carnoy seems to have 

 been the first to call attention to this second mode, and this is a 

 further proof of the identity of animal and vegetable cells. 



The second kind of cell-division, is called, by Flemming, in- 

 direct; Carnoy calls it kinetic,! e., following certain movements 

 in the nucleus. This kind of cell-division is effected in the fol- 

 lowing wa)^ : When the nucleus becomes active, in its prepara- 

 tion for division, the nuclein tubule contracts and becomes 

 shorter and thicker ; next it breaks up into a number of short 

 pieces (rodlets), which are curved or undulate or rarely straight. 

 Thus far no movement has taken place either in the nucleus or 

 protoplasm. After this, the nuclein rodlets begin to move to- 

 wards the equatorial line and soon are arranged in two rows, 

 forming an equatorial crown. Now the nucleus becomes slightly 

 elongated, and at the same time the cell protoplasm enters into 

 activity — the asters are formed in it and the reticulum soon is 

 seen arranging itself in radiating lines from them. After this 

 the nuclein rodlets move towards the asters; the nuclein mem- 

 brane disappears, the nuclein forms the polar crowns and the 

 nuclear protoplasm assumes the well-known spindle-shape. At 



