LARVAE OF ARBACIA PUNCTULATA 323 



also fundamental alteration in physical characters, — mainly 

 increased osmotic pressure in the blastocoele, resulting in infla- 

 tion and death. Fischel believed that these substances, which 

 played so important a part in regulating oxidations in artificial 

 parthenogenesis, were intrinsically harmful, but were controlled 

 by the processes set into action by membrane-formation. He 

 observed, as had the previous investigators, that, while the 

 limits of endurance for the different Echinoids employed were 

 narrow and about the same for all, yet the response to environ- 

 ment was not absolutely identical for all the species nor for all 

 the individuals of the same species. 



Hyper- and hypo-tonic solutions were emplo3^ed by Vernon 

 ('95), who diluted and concentrated the natural sea-water to 

 the limits of endurance, ranging from al^out 850 cc. diluted 

 to a liter on the one hand, to 1150 cc. concentrated to a liter 

 on the other. He found that the maximum growth was attained 

 in a solution containing 50 cc. of distilled water per liter and 

 resulted in a 15.6 per cent increase in size. 



The variations in early development produced by changes of 

 temperature have been the subject of numerous investigations. 

 One of the earliest observations recorded on this subject was 

 that of Herbst ('95). While he did not report any direct effect 

 of temperature on the developing embryos, he believed that the 

 markedly different response to experimental conditions shown 

 by the eggs of two successive years, was due to the difference in 

 temperature of the sea-water of the regions from which the eggs 

 and sperms were obtained. 



The effects of temperature and season on development were 

 made the subject of a detailed investigation by Vernon ('95). 

 He concluded that the larvae of Strongylocentrotus lividus 

 ''reach their maximum body length when impregnation is per- 

 formed at about 17°.5 to 21°. 5, whilst at temperatures above or 

 below these limits, the larvae become smaller, and that too in 

 greater proportion the more the temperature varies from the 

 favorable limits." Subjection to the altered temperature for 

 one minute during fertilization proved quite as effective as 



