III. 8 CHEMICAL COMPOSITION 131 



however, both male and female nuclei are able to divide, this 

 division must be normally incited, not by their union with one 

 another, but by the separate action of the cytoplasm on each, 

 a view which is fully borne out by the phenomena of artificial 

 parthenogenesis and merogony (the development of fertilized 

 enucleate egg fragments), whatever interpretation may eventually 

 be put on the ' contractility ' of the cytoplasm. 1 



Another alkaloid which exerts an injurious influence on the 

 ova of Echinoderms is atropine, the sulphate of which retards 

 and dwarfs the development of Asterias and Arbacia (Mathews). 

 Pilocarpine, on the contrary, has an accelerating effect, a result 

 attributed by Mathews to its activity as an oxidizer, while 

 atropine is regarded as a reducing agent, the property to which 

 Loeb has also assigned the value of potassium cyanide in pro- 

 longing the life of unfertilized ova. The eggs of sea-urchins, 

 when once laid, are only capable of fertilization and develop- 

 ment within a certain definite limit of time, after the expiration 

 of which they degenerate and die; after twenty-four hours, 

 for example, they are only able, when fertilized, to reach the 

 gastrula stage, and after thirty-two hours even fertilization is 

 hardly possible. By treatment with an appropriate solution of 

 potassium cyanide this limit may be considerably postponed. 

 In the most successful series of experiments the ova were first 



at 



placed in a solution of KCN in sea- water, and then 



750 



removed successively every twenty-four hours to 



1400 ^000' 



% fi 



, . In the last solution they were kept for various 

 <vOOO oOOO 



lengths of time, then removed to pure sea-water and fertilized. 

 As the table shows (Table XVII), segmentation was still possible 

 after 168 hours' sojourn in the solution, but the greatest number 

 of Plutei was obtained after only 66 hours' stay. 



It was also shown that better results could be obtained with 

 artificial parthenogenesis if the ova were first kept in the 

 cyanide solution. Loeb points out that in the higher animals 



1 Strictly speaking, only the division of the male chromosomes can be 

 regarded as being stimulated by the egg cytoplasm. What exactly it is 

 which excites the female nucleus to divide is not at all clear. 



K 2 



