FERTILISATION 231 



Morgan ^ found that an addition of sodium chloride to sea-water 

 containing ova of sea-urchins caused these to form astrospheres, 

 while, if the ova were afterwards transferred to ordinary sea-water, 

 they sometimes proceeded to segnient. The latter process, however, 

 was not normal, since the ova that had been subjected to this 

 treatment became transformed into masses of minute granules, and, 

 instead of acquiring cilia and giving rise to embryonic individuals, 

 they underwent a process of disintegration. 



To Loeb belongs the credit of having done more than any other 

 worker to elucidate the physico-chemical aspects of the phenomena 

 of fertilisation. Loeb was the first definitely to succeed in producing 

 plutei from the unfertilised eggs of the sea-urchin. His original 

 method was to expose the eggs for about two hours to sea-water in 

 which the degree of concentration had been raised .by about forty or 

 fifty per cent. This effect could be produced by the addition of 

 sodium chloride, but it was found to be immaterial what particular 

 substance was employed to raise the concentration, so long as it was 

 one which did not act injuriously 'on the eggs. The ova were 

 afterwards restored to normal sea-water, when they began to 

 undergo segmentation and subsequently developed into normal 

 " plutei. 



Loeb was able to show, further, that the parthenogenetic develop- 

 ment of the ova in such cases was brought about by a loss of water. 

 Thus, when the concentration of the sea-water was less than forty 

 per cent., some of the ova of the sea-urchin Arlatia could be induced 

 to develop, even though they were allowed to remain in the 

 hypertonic solution. By adopting similar methods a like result 

 could be effected for the other species of sea-urchin, and also in the 

 case of the starfish Asterias forhesii ; but 'it was necessary, as a 

 general rule, to restore the ova to normal sea- water, as the 

 continuance of abnormal conditions, although it might not hinder 

 segmentation, usually arrested the further course of development.^ 



It was founfl, however, that osmotic fertilisation differed in 



several respects from fertilisation by a spermatozoon. Firstly, the 



• ova fertilised by the former method began to segment without 



developing a membrane such as is invariably formed in normal eggs 



shortly after the entrance of the spermatozoa. Secondly, the rate of 



' Morgan, " The Action of Salt Solutions on tlie Unfertilised and Fertilised 

 Ova of Arbacia, etc.," Arch. f. Entwick.-Mech., vol. ill., 1896, and vol. viii., 1899. 



2 Loeb (J.), "On the Nature of the Process of Fertilisation, etc." Amer. Jour, 

 of PhysioL, vol. iii., 1899. " On the Artificial Production of Normal Larvse from 

 the Unfertilised Eggs of the Sea-Urchin (Arbacia)," Amer. Jour, of Physiol., 

 vol. iii., 1900. "On Artificial Parthenogenesis in Sea-Urohins," Science, vol. xi., 

 1900. " Further Experiments on Artificial Parthenogenesis, eto." Amer. Jour, 

 of Physiol., vol. iv., 1900. These papers are reprinted in Loeb's Studies in 

 General Physiology, vol. ii., Chicago, 1905. 



