564 E. BAY LANKESTER. 



attemptiug' to characterise tliem iu such, away as will indicate 

 their probable affinities and genetic history. 



Sob-phylum ARTHROPODA.— The characters of the sub- 

 phylum, and those of the associated sub-phyla Chtetopoda and 

 Rotifera, have been given above_, as Avell as the general 

 characters of the phylum Appendiculata which comprises 

 these great sub-phyla. 



Grade A. — Hyparthropoda. 



Hypothetical forms. 

 Grade B.— Protarthropoda. 



(a) The integument is covered by a delicate soft cuticle 

 (not firm or plated) which allows the body and its appendages 

 great range of extension and contraction. 



(6) The paired claws on the ends of the parapodia and the 

 fang-like modifications of these on the first post-oral append- 

 dages (mandibles) are the only hard chitinous portions of the 

 integument. 



(c) The head is deuteroguatlious_, — that is to say, there is 

 only one prosthomere, and accordingly the first and only pair 

 of hemignaths is developed by adaptation of the appendages 

 of the second somite. 



(d) The appendages of the third somite (second post-oral) 

 are clawless oral papilla3. 



(e) The rest of the somites carry equi-formal simple append- 

 ageS; consisting of a corm or axis tipped with two chitinous 

 claws and devoid of rami. 



(/) The segmentation of the body is anomeristic, there 

 being no fixed number of somites characterising all the forms 

 included. 



((/) The pair of eyes situated on the prosthomere are not of 

 the Euarthropod type, but resemble those of Chsetopods (hence 

 Nereid-ophthalmous) . 



(/<-) The muscles of the body-wall and gut do not consist of 

 transversely striped muscular fibre, but of the unstriped tissue 

 observed also in Cluutopoda. 



(i) A pair of cuulomoducts is developed in every somite, 



