XX 



INTRODUCTION 



TO THE SECOND EDITION. 



The progress of Biological Science, since the first issue of 

 this Synopsis in 1874, has suggested certain very desirable 

 improvements in the disposition of the groups within their 

 respective sub-kingdoms. For example, the Hydrocorallhue 

 now occupy groups 16 and 17. Nothing has occurred to 

 diminish the expediency, in a linear arrangement, of keeping 

 the Annuloid and Annulose sub-kingdoms near together. 

 The desiderata of the collection in typical forms have been so 

 far supplied that it is hoped that students of invertebrate 

 animals, adopting any of the various recent systems of 

 arrangement, may have no difficulty in finding in the series, 

 examples of such genera and species as they may require to 

 see, or others in close affinity with them. Instances in which 

 animals separated by characters of high biological significance 

 are found included in the same group are not very numerous, 

 and are generally noticed where they occur. Future and, 

 perhaps, extensive changes in the order of the groups may be 

 required when the indications of genetic affinity are better 

 understood. But until evolution through deprivation is as 

 fully recognised as evolution through accession, systematic 

 Biology will not be free from extravagant prominence and 

 significance given to obscure forms, the results, in a 

 descending order, of parasitism, or other abnormal habits 

 of life. 



Since the first issue of the Synopsis, the kindness of the 

 Committee has enabled me to publish, at the price of one 



