FERTILIZATION AFTER INITIATION OF DEVELOPMENT. 2JI 



capable of being fertilized, but on the contrary many eggs 

 that have failed to respond outwardly to the activating influ- 

 ences, by segmenting, are found to be incapable of fertilization. 

 The reaction differences of the eggs or their different physiological 

 states assert themselves by the variety of reactions given by the 

 egg after insemination; one egg will segment and produce a 

 swimming larva; another will divide a few times but finally 

 disintegrate; yet still another will remain to all appearances 

 in a normal condition, being normal in size and color, will be 

 surrounded with spermatozoon and yet does not divide; while 

 finally one will retain its full rounded appearance but give up 

 practically all its pigment content to the surrounding water, 

 but does not segment. If the eggs are given the optimum 

 exposure for cleavages, 1 insemination does not increase either 

 the percentage of swimming larvae or of cleavages. 



Professor Loeb, however, makes the claim that sea-urchin 

 eggs may undergo activation, from an exposure to hypertonic 

 sea-water, to such an extent that they segment once or twice, 

 as the case may be, but are nevertheless still capable of fertili- 

 zation. Quoting from Loeb: 2 



"When we put the unfertilized eggs of Strongylocentrotus 

 purpuratus directly into hypertonic sea-water . . . and if we 

 put them back at different intervals into normal sea-water, we 

 find that if eggs have been exposed a sufficiently long time (two 

 hours or more) to the hypertonic sea-water a number will begin 

 to segment. These eggs will often go into the two- or four-cell 

 stage, or sometimes to the eight- or sixteen-cell stage, and then 

 stop developing . . . such eggs remain after this perfectly nor- 

 mal and they have the appearance of small unfertilized eggs. 

 If we wait for sometime, say twenty-four hours, to make sure 

 that they neither develop nor disintegrate, and add sperm, each 

 one of these blastomeres forms a tightly fitting membrane. 

 They begin to develop in a perfectly normal way and into normal 

 larvae." 



Whether or not the fundamental principles of development 

 in the egg of Arbacia differ from those of 5. purpiiratns, the 



1 In this particular experiment an exposure to the stronger solution for 30 

 minutes. 



2 " Art. Par. and Pert., p. 237. 



