292 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



This statement will become much clearer by a few illustra- 

 tions. Figs. 78-80 are (five-days-old) plutei of purpuratus 

 produced by artificial parthenogenesis. They are identical 



Fig. 78 Fig. 79 Fig. 80 



FIGS. 78-80. Five-days-old plutei of S. purpuratus, produced by artificial 

 parthenogenesis. 



with the pure breed of purpuratus. Figs. 81-83 are three plutei 

 produced by fertilizing the sea-urchin egg (purpuratus) with 

 the sperm of the starfish. They are identical with the plutei 

 produced by artificial parthenogenesis. 



Fig. 81 Fig. 82 Fig. 83 



FIGS. 81-83. Five-days-old plutei from 5. purpuratus 2 and Asterias $ 

 The plutei are identical with the parthenogenetic plutei. 



If, however, the egg of S. purpuratus is fertilized with the 

 sperm of S. franriscanus, a closely related form, a pluteus of 

 an altogether different type is produced (Figs. 84-86). The 

 skeleton has the rough appearance of the franciscanus pluteus 

 and the typical arm formation characteristic of this paternal 

 form. It is therefore obvious that heterogeneous hybridiza- 

 tion is in reality artificial parthenogenesis with this difference 



