SECT. XII RELATION OF APUS TO CRUSTACEA 175 



carnivorous Annelid, and, secondly, that the living 

 Crustacea, excepting Limulus and (?) the Ostracoda, 

 may be easily deduced from the Apodida,\ 



If these points can be established, they necessarily 

 involve a rearrangement of the present system of 

 classification. The discovery that an animal, which 

 has hitherto been considered as a very specialised 

 form of a special group, is in reality one of the 

 simplest and most original forms of all the groups, 

 supplies at once the starting-point for the classifi- 

 cation of the Crustacea which has hitherto been 

 wanting. It is at present impossible to find points of 

 connection, sufficient for a natural system of classifi- 

 cation, between many of the different groups. We 

 shall now find that the acceptance of our Annelid 

 ancestor of Apus as the original form enables us, for 

 the first time, to sketch, at least In outline, a natural 

 order, not only embracing the Entomostraca and 

 Malacostraca, but also Limulus, the Eurypterld^, 

 and the Trilobites. This new classification we shall 

 attempt, that Is, if we are justified In calling that 

 " new " which is In reality only a further development 

 of views expressed many years back by the older 

 zoologists, and notably by Burmeister. 



Although we have set ourselves this double task, it 

 Is clearly impossible, In a small work like this, to go 

 Into many details, especially in our comparison of the 

 Apodldae with the many living Crustacean forms. It 

 will, w^e think, be granted, that a successful grouping 

 of the Apodidee with the Xiphosurldai, the Trilobites, 

 and other early forms as common derivatives from a 



