1905.] the Development of Eggs of Plaice and Echinus. 139 



which was the greatest strength employed, had killed only 65 per cent, of the 

 10-days-old eggs. Acids, above a small concentration, had a remarkably 

 stronger effect — in one day even 10-days-old eggs being killed by 10 c.c, and 

 the two other batches by 6 c.c. 



When working with the larger quantities of alkalies, it was very difficult 

 to tell exactly when an egg was dead. In the first experiments the point 

 was taken at which the egg began to become opaque, but, as soon as the 

 percentage of alkali present exceeds a very small amount, precipitation of 

 calcium and magnesium hydrates takes place, which renders observation 

 of such a change in the transparency of the egg difficult. Loeb, in his 

 experiments on Fundulus,* finds that the precipitate itself acts injuriously 

 upon the eggs, and that, if this be filtered off, the eggs will live and 

 develop in much stronger solutions than they would otherwise do. The process 

 of filtering off the precipitate before placing the eggs in the solutions was not 

 tried in the course of these experiments, they having been carried out 

 previously to the reading of Loeb's paper. 



Hitherto, it has always been considered that the young larva, on first 

 hatching from the egg, enters upon the most critical stages in its career, 

 and is at that time most susceptible to external influences, but the experi- 

 ments here carried out appear to show a resistance steadily increasing with 

 age, and that, even after the rupture of the egg-capsule, the young larva is, at 

 all events, no more susceptible than just before that event. It may be 

 suggested that this steadily increasing resistance is due to the gradual 

 development of the epidermal cells, which would form a protection to the 

 young embryo more or less impervious to the surrounding solution. 



Tables III, IV, and V give the actual experimental data on which Table I 

 is founded, and of which it is a risumL Table VI is introduced with the 

 object of laying emphasis on the statement as to the resisting powers of the 

 older eggs. It shows the percentage of these eggs which succeeded in 

 hatching in spite of the very unnatural conditions (stagnant water, possible 

 overcrowding, etc.) in which they were placed. Incidentally may be noticed 

 the very deadly effect of "di-methyl," to which attention is now to be 

 drawn. 



II. Effect of Indicators on Pleuronectes and Echinus. 

 The effects which di-methyl-amido-azo-benzol and phenol-phthalein produce 

 upon living organisms, as illustrated by the eggs of Pleuronectes and Echinus 

 esculentus, were accidentally discovered in the course of these experiments. 

 These indicators were originally added to the contents of some of the 



* 'Arch. f. Entwickelungsmechanik,' vol. 7, p. 631. 



