STRUCTURE AND DEVELOPMENTAL RATE 175 



In many of the experiments the available oxygen supply was 

 further reduced by first boiling and driving the air out of the 

 sea-water into which the eggs were to be placed. The central 

 eggs of large clusters in this boiled water frequently had their 

 development stopped in various stages, while other specimens 

 progressed at an extremely slow rate. One group of such experi- 

 ments will be briefly reviewed as illustrating the general results 

 from all. 



Experiment 915. A large number of eggs, from three females, was 

 fertilized by a single male. After 3 hours they were almost all devel- 

 oping and presented the typical 4 -cell stage. About 75 of these eggs 

 were placed in ordinary sea-water and separated apart on the bottom 

 of a dish to be developed as a control., The other eggs were divided 

 into three lots. Two lots were placed in dishes containing sea-water 

 that had been boiled, and the third lot was put in ordinary sea-water. 

 The eggs in the three dishes were then moved gently around until 

 they became clustered into large groups of about 100 or more. 



After 2 days of development, the control contained well-formed 

 embryos with the optic vesicles prominently shown and with 8 to 10 

 pairs of somites present. Many eggs on the outer parts of the clusters 

 in the unboiled sea-water wxre equally as far along, while others 

 near the center of the clusters were still in segmentation stages, and still 

 others were in various degrees of arrested development. The two lots 

 in l)oiled sea-water were in closely similar conditions. 



When 8 days old, the entire experiment was carefully examined and 

 the following conditions found. The control eggs all contained normal 

 embryos except for the fact that 3 specimens were smaller than the 

 others and somewhat delayed in development. These, however, later 

 succeeded in hatching. 



The clusters in unboiled sea-water contained many dead eggs. The 

 more superficial eggs of the cluster contained in general normal embryos, 

 though some were behind the control in their degree of development. 

 Almost all of the more centrally placed eggs of the group were several 

 days slower than the control in their developmental stages. These 

 embryos were small and pale with poorly expanded chromatophores, 

 and 15 of them, or 13 per cent of the small embryos, showed gross 

 abnormalities. They possessed narrow undeveloped heads, defective 

 eyes, deformed hearts with no circulation, and other common defects, 

 while 2 of the larger better developed specimens were double-headed 

 embryos. This dish contained a few more than 200 eggs, thus only 

 about 1 per cent developed double conditions. 



The first group that had been clustered in the boiled sea-water 

 showed a somewhat better record than the preceding. Here also 

 many of the eggs had died. There were again a number of normal 

 embryos in the superficial regions of the cluster. The more centrally 



