270 EMBRYOLOGICAL INVESTIGATIONS 



2. Partly from a fertilised ovum, and partly 



from unfertilised follicle cells. Examples: 

 Salpa and Pyrosoma. 



3. From a single fertilised ovum, together 

 with a greater or less number of yolk 

 cells, which are at first independent 

 cells, but which ultimately become 

 absorbed into the ovum. Examples: 

 Fasciola, Pisidium. 



4. From a single fertilised ovum, aided by 



nutrient matter derived from the sur- 

 rounding follicle cells. Examples : Ce- 

 phalopoda, and most Vertebrates. 



5. From a single fertilised ovum, without 



the aid of follicle cells. Example: 

 Amphioxus. 



6. From an unfertilised cell, or ovum. !r- 



amples : The parthenogenetic ova of 

 Entomostraca or of Rotifera. 



7. From one or more of the blastomeres 



resulting from the segmentation of a 

 fertilised ovum. Examples: Echinus, 

 Amphioxus. 



8. From a portion, large or small, of the 



body of the parent. Examples : Hydra, 

 Sponge. 



9. By local proliferation of the cellular 



elements of the parent, forming an 

 external or internal bud. Examples : 

 Sporocyst, Hydra. 



