220 THE PHYSIOLOGY OF REPRODUCTION 



water saturated with chloroform induced the unfertilised 

 eggs of the sea-urchin to develop membranes. Herbst l more 

 recently showed that benzol, toluol, creosote, or oil of cloves 

 produced a similar effect. Loeb 2 found that amylene and various 

 other hydrocarbons and acids also called forth membrane forma- 

 tion, and that eggs which were subjected to these methods 

 could be made to segment by subsequent treatment with hyper- 

 tonic sea-water in the way described. The substances which 

 called forth membrane formation can be divided into two 

 groups, the first consisting of hydrocarbons and certain sub- 

 stitute products, and the second being comprised of certain 

 acids. Loeb states also that the order in which the two agencies 

 are employed is of vital consequence, for if the eggs are sub- 

 jected to the membrane-forming solution after being placed in 

 the hypertonic sea- water instead of before, they develop a 

 membrane, but shortly afterwards disintegrate. As a result 

 of this series of experiments he concludes that the process of 

 membrane formation is an essential and not a secondary pheno- 

 menon. 3 He makes the further suggestion that membrane 

 formation is brought about by a kind of secretory process, due 

 to the squeezing out under pressure of a liquid substance from 

 the interior of the ovum 4 (cf. Jenkinson, p. 189). According to 

 this view the excretion of the fluid is the essential feature, while 

 the actual formation of the membrane is probably only a 

 secondary mechanical effect of the sudden secretion. 



In the case of the starfish it was found that the process of 

 artificial membrane formation was alone sufficient to induce 

 parthenogenetic development without any further treatment 

 with hypertonic sea-water. This observation is connected by 

 Loeb with the fact that starfish eggs are sometimes able to 

 develop in the absence of any external cause or agency. 



1 Herbst, "Uber die kunstliche Hervorragung von Dottermembranen," 

 &c., Biol. Centralbl., vol. xiii., 1893. 



2 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. 



3 It was found, however, that in the case of the starfish a very small 

 number of eggs could develop without first forming a membrane, and that 

 this number could be increased by transitorily treating the eggs with 

 acidulated sea-water. See below. 



4 Loeb,"Ueber die Natur der Losungen," &c.,Pfluger's Arch. , vol. ciii., 1904. 



