344 ABSTRACTS OF PAPERS. [VOL. II. 



ones of Demoor on the division of plant cells in vacua, or in 

 an atmosphere of CO 2 , and to those of Loeb and Norman on 

 Arbacia eggs in sea water concentrated by the addition of a 

 small percentage of chloride of sodium or magnesium. If the 

 strength of the ether solution be now somewhat reduced, by 

 evaporation or by the addition of sea water, the asters reap- 

 pear, though not attaining full development, and progressive 

 nuclear division may occur without cytoplasmic cleavage. In 

 this case the egg may give rise to a syncytium, containing 

 from four to sixty-four or more nuclei, which migrate towards 

 the periphery so as to take up nearly the same position as 

 they would have had in a segmented blastula. This phenomenon 

 strikingly recalls that which normally occurs in the cleavage of 

 many arthropod and some coelenterate eggs. At each nuclear 

 division an attempt is made at a corresponding cytoplasmic 

 division, but this is usually unsuccessful ; or, in case division 

 occurs, the cells subsequently fuse together to repeat the 

 attempt at the next nuclear division. This, again, is closely 

 similar to the ineffective early attempts at cleavage in such 

 eggs as those of Renilla. If the eggs be replaced in sea water 

 when the process is not too far advanced (4-32 nuclei), cleavage 

 may occur of a multiple type almost exactly like that occurring 

 in Renilla, and a normal blastula may arise ; but the cleavage 

 is often irregular or incomplete. 



These observations support the conclusion indicated in the 

 preceding paper, that the astral rays are not fixed and per- 

 manent structures, but an expression of a form of cytoplasmic 

 activity, partly in the nature of protoplasmic currents, that 

 may be inhibited by temporary paralysis of the cytoplasm. 

 They indicate also that the astral rays are connected with 

 cytoplasmic rather than with nuclear division, and support the 

 interpretation, offered by the author many years ago, of the 

 variations of cleavage observed in Renilla. 



B. 



If Toxopneustcs eggs be placed in 2.5/0 ether solution one 

 minute after fertilization, formation of the sperm-aster is com- 

 pletely suppressed. The sperm nucleus, however, slowly moves 



