538 CELL DIVISION IN EGGS OF CREPIDULA. 



action becomes a very important factor. For this reason a weak solution acting for 

 a long time leads to the greatest possible departures from typical development (Exps. 

 808, 821, 966-968, 833, 836, etc.; figs. 195, 196, 200, 208, etc.). On the other 

 hand eggs which have been subjected to strong solutions for a short time may 

 afterwards develop quite normally; thus in Exps. 815 and 816, 978-980, 3 per 

 cent, and 4 per cent. NaCl acting for 1 hr. completely stop all development for 

 the time being, but when the eggs are afterwards put into normal sea water devel- 

 opment goes on in a typical manner; on the other hand if these solutions act 

 for 4 hrs. or longer all cleavage is permanently stopped even though the eggs be 

 put back into normal sea water. This fact is shown still more strikingly in 

 Exps. 981-987 in which 5 per cent, or 6 per cent. NaCl is allowed to act for y 2 

 to % hr. after which the eggs may develop quite typically when put back into 

 normal sea water. From these experiments it is quite evident that the injurious 

 effects of hypertonic solutions are due primarily to their influence on kinetic 

 rather than on static phenomena, and particularly upon the divisional phenomena 

 of the cell. In all my experiments eggs are much more susceptible to injury 

 during division than during rest, and when abnormalities of division are once 

 started they rarely, if ever, right themselves. It is owing to these facts that 

 relatively weak solutions acting for a long time (during which developmental 

 processes proceed in abnormal directions), lead to the most extreme forms of 

 abnormalities. 



My observations on the effects of hypertonic solutions on cell division con- 

 firm the conclusions of practically all investigators who have dealt with the 

 subject, while at the same time they contribute certain new details and inter- 

 pretations. The immediate effects of hypertonic solutions on cell division fall 

 into one or another of the following classes: (1) Suppression of yolk division 

 without suppression of protoplasmic, nuclear, or centrosomal division. (2) Sup- 

 pression of division in yolk and protoplasm, without its suppression in nucleus 

 or centrosome. (3) Suppression of all forms of division, without stopping 

 nuclear growth or killing the cells. This suppression of division in each of these 

 cases may be temporary, the division starting again when the eggs are returned 

 to normal sea water, or it may be permanent, depending upon the strength of 

 solution used and the time of its action. In addition to these effects of hyper- 

 tonic solutions on cell division the following general effects on the different parts 

 of the cell may be noted: (4) Shrinkage of plasma, nuclei, chromatin, and 

 mitotic figures. (5) Formation of cytasters and polyasters. (6) Irregularities 

 in movements of chromosomes. (7) Separation of chromatin and achromatin. 



1. Suppression of Yolk Division without Suppression of Protoplasmic, Nuclear, 

 or Centrosomal Division. 



(Figs. 159-170, 197-208, 211-216.) 

 In weak salt solutions (}4 per cent. KC1, 1 per cent. NaCl, 2 per cent. MgCl 2 ) 

 division of centrosomes and nuclei may proceed slowly, while division of yolk is 



