TJie hifluence of External Factors oji Dcvclopnirnt 187 



Short embryos with open blastopores were formed in many cases. 

 The heart was weak and tubular with feeble contractions and was 

 surrounded by a swollen pericardium. One embryo when eleven 

 and one-half days old hatched in a 2V m solution, but was unable to 

 swim. In many of these embryos no heart beat could be detected 

 and the yolks were badly shrunken. In one case a one-eyed 

 embryo was noted, this is mentioned on account of the tendency of 

 magnesium salts to produce such a condition, but the eye structures 

 of this embryo were very imperfect and no lens was present, this 

 condition will be found to differ entirely from that described below 

 as caused by the action of MgCK. 



Eggs were subjected to MgCl2 solutions of the following 

 strengths to m, ^ m, i m, and \ m in distilled water, and 0.238 m, 

 0.25 m,o. 286 m, 0.33 m and 0.5 m in sea-water; a molecular solution 

 of MgCl2.6H20 being equivalent to about a 20.3 per cent solution. 

 The early development in all of these solutions is strikingly normal 

 considering the large death rate which occurs during these stages. 

 The salt seems especially toxic to the early embryo. At seventy- 

 four hours some embryos are well formed, though behind the con- 

 trol in their development, and the blood circulation is slow in some 

 while others have a quick heart action. When ten days old all are 

 weak and smaller than the control, the blood flow is slow and spas- 

 modic; in some embryos the circulation has ceased and the blood 

 is collected in the sinus and heart and appears as a red streak in 

 front of the head. Many of the livelier embryos wave their pectoral 

 fins. 



In the J m and i m distilled water solutions many embryos 

 hatch when about fifteen days old, though they swim abnormally 

 on account of their bodies being twisted. The sea-water solutions 

 cause the yolks to shrink and in these the embryos are also small 

 with sluggish circulations. Although kept alive for twenty-four 

 days none of the eggs in the sea-water solutions would hatch. 



The conditions cited above are general and occurred also in a 

 number of different salt solutions, but the condition which may 

 now be considered seems peculiarly characteristic of the Mg salt. 

 In the^m sea-water solutions one-eyed embryos occurred with sur- 

 prising regularity in 50 per cent of the eggs. This experiment 



