THE AXXALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



[SIXTH SERIES.] 



" ptT litora spargite museum, 



Kaiades, et circiim vitreos eonsidite fonti's: 

 PoUice virgineo teni-ro8 hie carpite flores: 

 Floribus et pictura, divse, ri'i>lete canistrum. 

 At T08, o Xyinpliae Craterides, ite sub undaa ; 

 Ite, recurrato variata corallia trunco 

 Vcllite muscosis e rupibus, et mihi conchas 

 Ferte, Deae pelagi, et pingui conchylia 8Ucco." 



N. ParlheniiGiannettasii Eel. I. 



No. 61. JANUARY 1893. 



I. — On some Points in the Morphology of the Arachnida 

 (s. s.), loith Notes on the Classification of the Group. By 

 il. I. POCOCK, of the British Museum (Natural History). 



[Plates I. & n.] 



Since it is generally admitted that the ancestor or ancestors 

 of the Arthropoda must be sought for in animals resembling 

 the Annclidan worms in the complete segmentation of the 

 body, it seems clear that a species in which the metamerism 

 is highly developed is, cctteris paribus^ more primitive than an 

 allied form in svhich it is obscurely manifested. The two 

 common decapod crustaceans, the crab and the lobster, furnish 

 a good example of the truth of this maxim, the latter animal 

 with itsgangliated nerve-chord, its long, segmented, and limb- 

 bearing abdomen, being unquestionably more nearly related to 

 the ])vimitive form or ancestor of the L)ecapoda than the crab. 

 Consequently in tracing the phylogeny of this group of crus- 

 taceans we should conclude that the Bracliyura are the descen- 

 dants of the Macrura, and that as sucli they should occupy a 

 higher branch of a genealogical tree. 



The truth of this, however, is so very obvious that the only 

 excuse to be offered for its restatement is the circumstance 

 that not all authors have boi'ne it in mind in dealing with the 



Ann. dD Mag. N. Hist. Ser. 6. VoL xi. 1 



