404 E. E. JUST. 



ments. It should be pointed out that the hypertonic sea-water 

 used in these experiments never gave membranes. Insemination 

 in normal sea-water of eggs that have had treatment with hyper- 

 tonic sea-water may give 100 per cent, membranes. 



We thus see that the egg of Arbacia that has such treatment 

 with hypertonic sea-water that mitosis starts up is capable of 

 responding to insemination during any phase of mitosis except the 

 terminal. So far as I have been able to determine, insemination 

 resulting in sperm penetration and perfect membrane separation is 

 as easy to obtain in the anaphase as in the normal resting stage. 

 The plutei from these eggs are as viable as normal plutei. 



With the onset of the cortical changes preceding first cleavage, 

 these eggs fail to respond to insemination. So far I have not 

 studied the effect of inseminating these eggs after first cleavage. 

 According to Loeb, however, the blastomeres of the egg of the 

 California sea-urchin induced to cleave through exposure to hyper- 

 tonic sea-water separate membranes on insemination. Moore, on 

 the other hand, was unable to obtain membranes after inseminating 

 isolated blastomeres of Arbacia eggs induced to cleave by exposure 

 to hypertonic sea-water. 



I have in my work encountered eggs that simulate first cleavage ; 

 in such eggs one of the " pseudo-blastomeres " on insemination 

 will form a membrane, cleave, and swim. The other member of 

 the pair never shows any trace of development. Such eggs seem- 

 ingly composed of two blastomeres may be easily produced in 

 large numbers. 



If eggs that have had an exposure to hypertonic sea-water be 

 shaken gently or squirted through a pipette into normal sea-water, 

 they appear as eggs in the two-cell stage. These pseudo-blasto- 

 meres may be equal in size or of all degrees of inequality in size. 



Such eggs on insemination form membranes around one com- 

 ponent only, regardless of its size. Thus one may get a large or 

 small cleaving egg within a membrane and subsequently a swim- 

 ming form, attached to an inert mass of cytoplasm without the 

 vestige of membrane. The explanation of this condition is simple. 



The hypertonic sea-water so alters the cortex of the egg that it 

 breaks when the egg is shaken and allows an outflow of endoplasm. 

 It is this endoplasm free of cortical material that fails to respond 



