1 88 FOOT-NOTES TO EVOLUTION. 



istics of both. Thus the hybrid presents a new type, 

 which was found to be likewise constant, and in no 

 case did it approach the likeness of either the Echinus 

 or SphcBrechinus type, so as to be mistaken for them. 

 Thus were established four preliminary essentials to 

 the experiment, viz. : 



1. The constancy of the normal Echinus larval type. 



2. The constancy of the normal SphcBrechinus larval 

 type. 



3. The constancy of the new hybrid type between 

 Echinus 5 and SphcBrechinus ? . 



4. The possibility of securing non-nucleated frag- 

 ments of SphcBrechinus eggs by shaking, which were 

 capable of fertilization, and from which dwarf larvae 

 might be reared. 



The crucial point in the experiment, as may have 

 been already anticipated, was to cross-fertilize non-nu- 

 cleated fragments of SphcBrechinus eggs with Echinus 

 sperm. The type of larva resulting would decide the 

 point in question. Here we may have a nucleus from 

 one species introduced into the non-nucleated cyto- 

 plasm of another species by a perfectly normal process 

 — i. e., by the penetration of the spermatozoan into the 

 ^%%. If the resulting larva be of the hybrid type, as 

 shown in Fig. 14, A and B, then nucleus and cytoplasm 

 both unite in determining the hereditary characteristics ; 

 if the pure SphcBrechinus type of Fig. 13, Cand D, results, 

 then the cytoplasm alone bears these influences; while, 

 finally, if the type be that of Fig. 13, A and B, to the 

 spermatozoan nucleus alone must be ascribed the heredi- 

 tary qualities. The larvae secured by Boveri were of 

 the pure Echifius or paternal type, as is well shown in 

 Fig. 14, C and D. A comparison of these figures with 

 Fig. 13, A and B, show unmistakably that this is the 

 case. No trace of the SphcBrechinus, or maternal, char- 



