216 THE PHYSIOLOGY OF REPRODUCTION 



Artificial Aids to Fertilisation 



It has been already recorded that cross-fertilisation between 

 certain species of Echinoderms can be effected by having re- 

 course to physico-chemical methods. It is not surprising, there- 

 fore, that fertihsation between individuals belonging to the same 

 species can be assisted, or caused to take place more frequently, 

 in the presence of certain substances artificially added. 



Thus, according to Roux, frog's eggs can be fertihsed more 

 readily by adding sahne solution to the water in which they 

 are deposited. Wilson says that in the case of the mollusc 

 Patella, a larger number of eggs can be fertihsed if potash 

 solution is added. "^ Dungern ^ states that the activity of 

 the spermatozoa in the sea-urchin can be increased in the 

 presence of substances extracted from the ova. Similarly it 

 is said that normal prostatic secretion has an exciting action 

 on mammahan spermatozoa (p. 236). Furthermore, Torelle 

 and Morgan ^ have shown that the immature spermatozoa 

 of starfish can be stimulated, and fertihsation can be induced, 

 by adding ether and various salt solutions to the sea-water. 



Artificial Parthenogenesis 



The fact that the ova of various kinds of organisms are 

 capable under certain circumstances of segmenting and de- 

 veloping into new individuals without the intervention of male 

 germ-cells, has been already referred to. In such animals as 

 the Aphidae this method of reproduction appears to be called 

 forth by certain conditions of temperature and moisture. In 

 other forms of life the necessary factors for the occurrence of 

 parthenogenesis are not so evident, but the fact of its existence 

 has been known from early times.* 



In many animals parthenogenesis has been observed to occur 



' For further information on this subject, with references to literature, see 

 Przibram, Enibryogeny, English Translation, Cambridge, 1908 ; and Jenkinson, 

 Experimental Embryology, Oxford, 1909. 



^ Dungern, " Neue Versuche zur Physiologie der Befruchtung," Zeitschr. 

 f. allgem. Phys., vol. i., 1902. 



' Morgan, Experimental Zoology, New York, 1907. 



' See footnote, p. 131. 



