130 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



is, however, 0.94 m, or isosmotic with sea-water. But this 

 solution acts just as hypertonically upon the sea-urchin egg as a 

 0.80 m NaCl solution, i.e., a solution whose osmotic pressure 

 is about 50 per cent higher than that of a 0.94 m cane-sugar 

 solution. 



It can be directly shown that a solution of cane sugar, 

 which is theoretically isosmotic with sea-water, is actually 

 hypertonic for the sea-urchin egg. For the eggs shrivel in such 

 a solution; they even shrink in a 7/8 m cane-sugar solution; in a 

 6/8 m solution they retain their volume and in a 5/8 m solu- 

 tion they increase in size. Eight years ago I also observed that 

 medusae (Polyorchis) shrink considerably in a pure cane-sugar 

 solution that is theoretically isosmotic with sea-water. 



It can be indirectly shown that a 3/4 m cane-sugar solution 

 is about the concentration that is isotonic for the sea-urchin 

 egg, by placing sea-urchin eggs that have been fertilized with 

 sperm in pure cane-sugar solutions of different concentrations 

 immediately after fertilization. Experiments of this description 

 showed that in a 6/8 m cane-sugar solution the first cell division 

 occurs in all the eggs of purpuratus, and indeed at almost the same 

 time as in normal sea-water; while in 5/8 and 7/8 m solutions its 

 onset is delayed and occurs in only a few eggs. In cane-sugar 

 solutions below 5/8 m and above 7/8 m as a rule not a single 

 egg divided. In 6/8 m cane-sugar solution, again, the cleavage 

 did not go beyond the four- or eight-cell stage, which is in 

 accordance with the experience in muscle. But if the eggs are 

 replaced in sea -water they develop normally. This behavior 

 of the egg in a cane-sugar solution corresponds to the behavior 

 of a medusa in the same solution : for in the latter, also, as well 

 as in the heart, the spontaneous contractions cease in a pure 

 cane-sugar solution. 1 These observations have a bearing upon 

 a controversy between Delage and the writer. Delage used in 

 his experiments on artificial parthenogenesis cane-sugar solu- 



1 Loeb, Am. Jour. Physiol, III, 384, 1900. 



