8 4 



CELL-DIVISION 



A no less remarkable mode of spindle-formation, which is in a cer- 

 tain way intermediate between the cormophyte-type and the usual 

 animal type is described by Mead ('97, '98, i) in the first maturation- 

 division of CJicetopterus. Here the completed amphiaster is of quite 

 typical form, and the centrosomes persist for the following mitosis ; 

 yet Mead is convinced that the amphiaster is synthetically formed by 

 the union of two separate asters and centrosomes (Fig. 150) which 



Fig. 34. Division of pollen-mother-cells in the lily as described by GuiONARD. 

 A. Anaphase of the first division, showing the twelve daughter-chromosomes on each side, the 

 interzonal fibres stretching between them, and the centrosomes, already double, at the spindle- 

 poles. B. Later stage, showing the cell-plate at the equator of the spindle and the daughter- 

 spiremes (dispireme-stage of Flemming). 6". Division completed; double centrosomes in the 

 resting cell. D. Ensuing division in progress ; the upper cell at the close of the prophases, the 

 chromosomes and centrosomes still undivided; lower cell in the late anaphase, cell-plate not yet 

 formed. 



have no genetic connection, arising independently de novo in the 

 cytoplasm. 1 Improbable as such a conclusion may seem on a priori 

 grounds, it is supported by very strong evidence, 2 and, taken together 



and nearly parallel fibres, each of which terminates in a deeply staining granule. Nearly 

 similar spindles have been described by Strasburger ('80) in Spirogyra, and in the embryo- 

 sac of Monotropa. It is not impossible that such spindles may represent a type intermediate 

 between the " cormoptyte " and " thallophyte " types of Muttier. 



1 Cf. p. 306. 



2 I have had the privilege of examining some of Mead's beautiful preparations. 



