NOMENCLATURE OF THE CCELOM 37 



15. A nephridium may, as may a uroduct or gonoduct, acquire 

 a secondary element by ingrowth of ectoderm at the nephridiopore, 

 its original external opening. This secondary portion must be 

 termed " NEEHRIDIODJEUM " (Goodrich), the word being formed in 

 the same way as stomodseum and ccelomodaeum. 



16. Nephridia may become "grafted" in various degrees upon 

 uroducts and gonaducts in some animals (e.g. the Polychsetous 

 Annelids), giving rise to organs of complex origin which cannot 

 be termed either " nephridia " or " coelomoducts," since they have a 

 part of each category in their composition. The composite organ 

 thus formed may be termed a " NEPHROMixiUM " or " NEPHROMix," 

 in reference to its hybrid composition. 



The object of this introductory chapter is now completed. 

 That object has been the vindication of the crelom as a morpho- 

 logical factor of primary importance in the animal series, and 

 the maintenance of the conclusion that the ccelom by its presence 

 justifies the separation of a higher grade of Enterozoa, the 

 Coelomocoala, from a lower grade the Enterocoela, in which it is 

 not differentiated as a separate cavity. 



