76 ON CLASSIFICATION. 



respects, Annelids differ widely from Arthropods. It may 

 be doubted whether any Annelid is devoid of cilia in some part 

 or other of its organization, and cilia constitute the most im- 

 portant organs of locomotion in the embryos of many. No 

 Annelid possesses a heart communicating by valvular apertures 

 with the perivisceral cavity, none have articulated limbs, and 

 none possess a head composed of even four modified somites. 



Most Annelids are provided with that peculiar system of 

 vessels termed " pseudo-hrenial ;" but, in some, that system has 

 not yet been discovered. 



In endeavouring to separate from among invertebrated 

 animals a first large group, comparable to the Vertebrata, it 

 appears to me that the resemblances between the Annelida and 

 the Arthropoda outweigh the differences ; and that the characters 

 of the nervous system and the frequently segmented body, 

 with imperfect lateral appendages, of the former, necessitate 

 their assemblage with the Arthropoda into one great division, or 

 " sub-kingdom," of Annulosa. 



But what of the Echinodermata and the Scohcida ? Should 

 both these great classes be also ranged under the Annulosa ; 

 or do they belong to different sub-kingdoms ; or, if they belong 

 to the same, should they constitute a sub-kingdom of their own ? 



I will endeavour to reply to these questions in succession. 

 Whether these two groups belong to the Annulosa or not, must 

 depend upon whether they possess any characters in common 

 with the Arthropoda and Annelida other than those which they 

 have in common with all animals. I can find none of any 

 great moment. No Echinoderm, or Scolecid, has a definitely 

 segmented body or bilaterally disposed successive pairs of 

 appendages. None of these animals lias a longitudinal chain 



of inmirlia. 



On the other hand, there is much resemblance between the 

 ciliated larvae of some Scolecids and Echinoderms, and those of 

 Annelids ; and the form of the body of many Scolecids is so 

 similar to that of one of the most familiar of Annelids, as to 

 have earned for both them and the Annelids the common title 

 of "worms." Nor must it be forgotten that, in the Annelids 

 there seem to be representatives <»[ that singular system of 



