2 C. M. CHILD 



difference in survival time, a death gradient (Child, '15 c, 16 a), 

 and, in many cases, certain changes preceding death, such as 

 change in state of aggregation of protoplasm, swelling and separa- 

 tion of cells or change in the color of a vital stain, for example, 

 neutral red, used as an indicator, are readily observed and show 

 the same gradient as the final death-change. With somewhat 

 lower concentrations the differential susceptibility may be made 

 evident as a differential inhibition, or, in cases of acclimation 

 or recovery, as a differential acceleration of development fol- 

 lowing a primary inhibition (Child, '16 c). In this work on the 

 polychetes, disintegration and death and inhibition of develop- 

 ment have been used as a means of demonstrating the differences 

 in susceptibility. Little can be accomplished with differential 

 acclimation because larval development is far advanced before 

 any considerable degree of acclimation occurs. 



For purely practical reasons, namely, because eggs and sperm 

 could be obtained at any time and in almost any quantity desired 

 from males and females kept in the laboratory, Chaetopterus 

 pergamentaceus was used as material to a greater extent than 

 other species, but Nereis limbata and Arenicola cristata were 

 also used so far as material was available, and some work was 

 done with Hydroides dianthus. Since a considerable number of 

 eggs must be used in each experiment and a considerable range 

 of concentrations of each agent used must be tested repeatedly 

 with different stages of development, an abundance of material 

 obtainable as desired is essential for any thorough study, par- 

 ticularly of the modification of development. The material 

 available has not been sufficient for all purposes, but certain 

 definite and characteristic results which permit certain , con- 

 clusions have been obtained. 



DISINTEGRATION AND DEATH GRADIENTS 



The gradients in disintegration and other protoplasmic changes 

 and in decoloration after staining with neutral red have been 

 demonstrated by means of various agents: KNC m/lOOO-m/100, 

 alcohol 2.5 to 5 per cent, HgCl2 m/500000-m/50000, CUSO4 

 m/lOOOOO-m/20000, NaOH m/10 approximately. These agents 



