446 NOTES ON PROSOBRANCHIATA, 



Both Harris and Jackson (7, 16) conclude that specific char- 

 acters make their appearance in the nepionic stage. This con- 

 clusion was, however, it is here contended, due to the misapplica- 

 tion of the terms, the stage in which they recognised these 

 specific characters being the neanic. 



That the nepionic stage, as defined above, exists throughout 

 whole orders no student of Ontogeny will deny. To cite the 

 example used later, the short stage during which the Lepidopterous 

 larva changes into the pupa cannot be regarded as embryonic, 

 neither can it be regarded as neanic, for certainly no specific 

 characters appear until the formation of the pupa, which must 

 therefore be regarded as neanic. Specific characters almost 

 invariably make their appearance in what these authors call the 

 nepionic (brephic) stage of the Gasteropoda. From an extended 

 study of Lotorium grow^th-stages, I find that it is possible to 

 identify almost any species of that genus from one-half whorl of 

 post-embryonic structure. On the other hand, it is often possible 

 to recognise a species from purely embryonic characters, e.g., 

 Triphora. But what is desired here is to point out that there 

 are whole orders in which the nepionic stage as above defined is 

 easily recognisable, whilst with the Gasteropoda, in that stage 

 which has hitherto been designated nepionic (brephic), specific 

 characters are generally recognisable. That is to say. the various 

 species of a given genus are already differentiated one from 

 another in that stage. The explanation lies in the fact that in 

 this class (Gasteropoda) the true nepionic stage is a ver}'^ transitor}'^ 

 one, and leaves, in most cases, no conchylaceous record. If this 

 be not recognised, the auxological terms will have one set of 

 meanings for Mollusca and another for other organisms. 



Cortiparison of Molluscan stages of deveJoj^mentiuith those of the 

 Lepidoptera. — That the various stages of development maybe the 

 better understood, it will be well to apply the auxological terms 

 to the Lepidoptera; organisms in which the primary divisions are 

 emphasised and easily definable, and then to homologise the 

 molluscan staj^es with them. 



