394 RALPH S. LILLIE 



the influence of two conditions, each of which forms an electri- 

 cal field negative centrally and positive peripherally: (1) that 

 due directly to the increase of surface-permeability, and (2) 

 that resulting from the diffusion of electrolytes from the chemi- 

 cally active centrosomal area. The total effect will be due to 

 a summation of these two influences. According to such a 

 conception, a response similar to that of irritable cells in gen- 

 eral, resulting in definitely localized metabolic effects, is an 

 essential factor in the mitotic process. 



The above general conception of the physico-chemical nature 

 of astral radiations is in agreement with many well known facts 

 of experimental cytology. The fact that astral centers or cen- 

 trosomes become active, i.e., develop radiations, concurrently 

 with the changes of form of the cell-body, is especially note- 

 worthy, and indicates a close connection between chemical 

 activity in these regions and alterations in the surface-tension 

 of the cell. Many indications point to the conclusion that this 

 relation is at times one of effect, the primary or initiatory con- 

 dition being the surface-change, as already suggested; at other 

 times it is apparently one of cause, i.e., asters, once formed, 

 may influence the surface-tension of the cell. The origination 

 of supernumerary asters or cytasters in dividing eggs appears 

 to illustrate the former condition; these structures, when pres- 

 ent in the cytoplasm along with the division-asters, undergo 

 parallel changes with the latter;*^ i.e., at the time when the cell- 

 body changes its form both the cleavage-centrosomes and the 

 supernumerary centrosomes simultaneously develop radiations 



*' Wilson describes this sj^nchronism in the behavior of cytasters and division- 

 asters in the egg of Toxopneustes (Archiv fiir Entwicklungsmechanik, 1901, 

 vol. 12, p. 529) : "It is a noteworthy fact that the whole cycle of changes involved 

 in the division of the cytasters takes place nearly synchronously with those in 

 the division-asters (p. 554)." Cf. also Kostanecki's observations on the parthe- 

 nogenetic eggs of Mactra (Arch. f. mikr. Anat., 1908, vol. 72, p. 327). Also Conk- 

 lin's studies on Crepidula eggs (Journal of the Academy of Natural Sciences of 

 Philadelphia, 1912, vol. 15, section on Cyasters and Polyasters, p. 542). These 

 structures appear to consist of the same material as cleavage-asters, and exhibit 

 closely similar behavior; Conklin regards the cytasters as "isolated portions 

 of archiplasm .... which take the aster form during mitosis and the 

 vesicular form during resting periods;" in polyastral mitoses and similar con- 

 ditions,- "all asters within the same egg are in divisional activity at the same 

 time." 



