174 CHARLES R. STOCKARD 



dishes, ordinary 'finger-bowls/ containing about 60 cc. of water. 

 The thread-like processes from the egg membranes become en- 

 tangled and cause the eggs to cluster together in bunches of from 

 a few to even as many as one hundred or more. 



It is a well recognized fact that in such clusters the conditions 

 for development of the individual eggs are not equal, and the 

 egg group fails to present a uniform mode of development. The 

 common practice is to separate the eggs in a dish so that they lie 

 apart and are not clustered together. The permanent separation 

 of the eggs requires care and attention, since they may again 

 become bunched by the agitation of the water. When they are 

 properly kept apart the entire lot in a dish will develop with 

 remarkable uniformity. 



No control group of Fundulus eggs should serve as a standard 

 for development unless the individual eggs are kept completely 

 free from contact with one another. In my experience, under 

 such conditions only the most insignificant percentage of develop- 

 mental abnormalities ever occur. I am convinced that the high 

 percentage of abnormalities recorded by certain experimenters 

 among their control sets are due to a failure to properly separate 

 the eggs. The clustered condition also vitiates the results ob- 

 tained from experimental groups of eggs. 



Advantage was taken of this tendency to become entangled 

 into clusters in order to study the developmental reactions of 

 eggs with more or less access to a free oxygen supply. The eggs 

 about the outside of such a cluster are in contact with fresh sur- 

 rounding water and a sufficient amount of oxygen for normally 

 rapid development. Those specimens lying deeper and deeper 

 in the cluster are more and more removed from a freely changing 

 water supply, and, therefore, experience various degrees of a 

 stagnating environment. Such eggs not only lack a constant 

 oxygen supply, but no doubt exist in an environment containing 

 an excess of waste products, such as the CO2 given off by their 

 neighbors. The developmental perfection attained varies directly 

 with the distance from the center of the egg cluster, the further 

 removed from the center the more perfect the development. 



