NDAIEXCLATURE OF STAGES IN ONTOGENY 971 



terms which are appHcable to the ontogenetic stages of development 

 of all non-colonial organisms, and hence deserve to be widely and 

 generally used. The ontogenetic cycle, or cycle of individual de- 

 velopment (Hyatt-20), is divided into the Embryonic and the 

 Ep-embryonic periods, and each is further subdivided into onto- 

 stages and sub-stages, as follows : 



Embryonic. { 



Ep-embryonic. { 



Onto-stage. 

 Prot-embryonic 



Mes-embryonic 



Met -embryonic 



Neo-embryonic 



Typ-embryonic 



Phyl-embryonic 



Nepionic 

 Neanic 

 Ephebic 

 Gerontic 



Onto Sub-stage. 



A na-prot-emhryonic 

 Meta-prot-embryonic 

 Para- prot-embryonic 

 Ana-mes-embryonic 

 { Meta-mes-embryonic 

 Para-mes-embryon ic 

 A na-met-ertibryonic 

 Meta-met-embryon ic 

 Para-met-em bryon ic 

 A na-neo-embryonic 

 Meta-neo-embryonic 

 Para-neo-embryonic 

 A na-typ-embryonic 

 Meta-typ-embryonic 

 Para-typ-embryonic 

 Ana-phyl-embryonic 

 Meta-phyl-embryonic 

 Para-phyl-embryonic 



Ana-nepionic 



Meta-nepionic 



Para-nepionic 



Ana-neatiic 



Meta-neanic 



Para-nea?iic 



A na-ephebic 



Meta-ephebic 



Fara-ephebic 



A na- gerontic 



Meta-gerontic 



Para-gerontic 



The sub-stages ana, meta, and para, or the early, intermediate, 

 and later sub-stages, are useful for more detailed subdivision 

 than is possible with the stages alone. The phyl-embryonic is the 

 only embryonic stage with which the palaeontologist has to deal. It 

 is the first stage in which hard parts capable of preservation are 

 generally formed. The phyl-embryonic stages of the following 

 classes of invertebrates have been definitely recognized and named : 



