232 THE PHYSIOLOGY OF REPRODUCTION 



development in the artificially fertilised eggs was considerably slower 

 than in the eggs fertilised by spermatozoa. Thirdly, the larvae 

 arising from osmotic parthenogenesis, as soon as they began to swim, 

 did so at the bottom of the dish in which they were placed, instead 

 of rising to the surface of the water lite normal larvae. It was 

 found also that the percentage of eggs which could be induced to 

 develop by the osmotic process was invariably very much smaller 

 than the percentage of normally fertilised eggs- which underwent 

 development. The consideration of these differences led Loeb to 

 conclude that the ^spermatozoon in normal fertilisation carried into 

 the ovum not one, but several substances or conditions, each of which 

 was responsible for a part only of the normal characteristics of the 

 process; and that, in order to imitate successfully the action of 

 the sperm, it would be necessary to combine two or more artificial 

 methods. 



When the eggs of Strongylocentrotus purpuratus were put into 

 50 cubic centimetres of sea- water to which 3 c.c. of a decinormal 

 solution of a fatty acid had been added, and were left in this water 

 for about a minute, and were then transferred to ordinary sea-water, 

 they were observed to form membranes. It was also noticed that 

 the eggs underwent internal changes characteristic of nuclear division, 

 but they were rarely seen to segment. Subsequently they began to 

 disintegrate, and after twenty-four hours were nearly all dead. If, 

 however, the ova, after they had formed a membrane, were deposited 

 in sea-water which had been rendered hypertonic by adding 15 c.c. 

 of sodium chloride solution of two and a half times the normal 

 concentration, to 100 c.c. of sea- water, all or nearly all the eggs could 

 be induced to develop. Furthermore, the rate of development was 

 practically the same as that of normally fertilised eggs, a large 

 percentage of the blastulse looked normal and rose to the surface of 

 the water, and the plutei which developed showed the usual degree 

 of vitality. 



The brothers Hertwig ^ had previously discovered that sea-water 

 saturated with chloroform induced the unfertilised eggs of the sea- 

 urchin to develop membranes. Herbst ^ more recently showed that " 

 benzol, toluol, creosote, or oil of cloves produced a similar effect. 

 Loeb 8 found that amylene and various other hydrocarbons and acids 

 also called forth membrane formation, and that eggs which were 

 subjected to these methods could be made to segment by subsequent 



1 Hertwig (O. and R.), Untersuchungen zur Morphologie mid Physiologie der 

 Zelle, Jena, 1887. 



2 Herbst, " tJber die kiinstliche Hervorragung von Dottermembranen, etc.," 

 Biol. Gentralbl., vol. xiii., 1893. 



^ Loeb, The Dynamics of Living Matter, New York, 1906. This work contains 

 further references. "On an Improved Method of Parthenogenesis," Univ. of 

 California Publications : Physiology, vol. ii., Berkeley, 1904. 



