94 MARY GRACE SPRINGER. 



Another fact which should be emphasized is that there was 

 very evidently a shorter length of life in cultures containing ex- 

 tract than in the controls. This lowered degree of vitality, or of 

 resistance, often manifested itself in a slower rate of movement, 

 particularly at the blastula stage. A possible explanation of this 

 effect may be found in part in the increased danger of bacterial 

 infection which the use of extract affords. The presence of the 

 crushed, and disorganized protoplasm of the extract affords a 

 splendid opportunity for the breeding of bacteria. Thus it must 

 be remembered that in considering the causes of the retardation, 

 and the malformations resulting from the use of the extract, the 

 matter of bacterial infection and more especially the effects of 

 the toxins produced by these bacteria should receive due emphasis. 

 It should be stated, however, that the experiments in which boiled 

 extract was used furnish some evidence, very slight though it may 

 be, that something other than bacterial action is involved in the re- 

 tardation and the malformation resulting from the use of the 

 extracts. 



SUMMARY. 



1. Extracts of Arbacia larvae in the 128 256-cell stage, in the 

 early and in the late blastula, gastrula, and pluteus stages, when 

 present in a sufficiently high concentration, definitely retard the 

 development of eggs of the same species. 



If these extracts are used in very low concentrations, the re- 

 tardation may well lie within the limits of experimental and ob- 

 servational error. 



2. The retardation noted is manifested slightly in the early 

 cleavage rates, and more markedly in the later stages of develop- 

 ment. 



3. Besides retarding development, these embryological extracts 

 often cause cytolysis, arrests of development, and a very noticeable 

 failure of the eggs to develop beyond the early non-motile blastula 

 stage. 



4. The very evident tendency of the eggs to stop at the blastula 

 stage suggests that possibly this stage is a stage peculiarly sus- 

 ceptible to the extract and characterized by a general lack of re- 

 sistance. 



