^66 E. HAY LANKESTER. 



■which form the limbs, the primitive axis or corm being 

 reduced and of insignificant size. In the most primitive 

 stock all the post-oral appendages had gnathobasic outgrowths. 



(/) The segmentation of the body is auomomeristic in the 

 more archaic members of each class, nomomeriatic in the 

 higher members. 



(g) The two eyes of Chtetopod structure have disappeared, 

 and are replaced by the Euarthropod eyes. 



[h] The muscles in all parts of the body consist of striped 

 muscular fibre, never of nnstriped muscular tissue. 



(i) The coclomoducts are suppressed in most somites, and 

 retained only as the single pair of genital ducts (very rarely 

 more numerous), and in some also as the excretory glands 

 (one or two pairs) . 



(j) The ventral nerve-cords approach one another in the 

 mid-ventral line behind the mouth. 



{k) The nerve cells of the ventral nerve-cords are segregated 

 as paired ganglia in each somite, often united by meristic 

 dislocation into composite ganglia. 



(l) The genital ducts may be the coelomoducts of the pen- 

 ultimate or antepenultimate or adjacent somite, or of a 

 somite placed near the middle of the series, or of a somite 

 far forward in the series. 



Class 1 (of the Euarthropoda). — Diplopoda. 



The head has but one prosthomere (monoprosthoraerous), 

 and is accordingly deuterognathous. This carries short-jointed 

 antennas (in one case bii-amose) and e\'es, the structure and 

 development of which require further elucidation. Only one 

 somite following the first post-oral or mandibular segment 

 has its appendages modified as jaws. 



The somites of the body, except in Pauropus, either fuse 

 after early development and form double somites with two 

 pairs of appendages (Julus, etc.) or present legless and leg- 

 bearing somites alternating. 



