OF THE ANNULOSA. 389 



the relations of affinity as above detailed, so that the cir- 

 cles of Crustacea and Arachnda shall touch at the points 

 Lcemodipoda and Phahnigidea, with the mere interven- 

 tion of the Pt/cttogonida as an osculant class, then it will 

 be perceived that the analogies which the two classes, 

 possessing a distinct circulation, bear to the contiguous 

 circles having no circulation, are reversed in order. If, 

 on the contrary, we pay attention, as in the subjoined table, 

 to the relations of analogy as well as of affinity, we have 

 the analogies between contiguous circles always observed 

 in their proper order ; biit then the Araneidea and Deca- 

 poda will be found near the osculant point of the classes 

 of Arachnda and Crustacea, while Cyamus and PJialan- 

 gium, which I perfectly agree with M. Savigny in think- 

 ing connected together by Pycnogonum, are at the oppo- 

 site although analogous points of their respective circles. 

 The only method by which at present I can explain this 

 remarkable circumstance, is by the affinity which opposite 

 points of a circle always bear to each other. As Pha- 

 /angium approaches near to Araiiea, and female Lamodi- 

 poda in some measure to Decapoda, the reader will per- 

 ceive how the Pycnogonida may form a point of union 

 for the four groups ; in other words, may be the centre of 

 that affinity which exists between an Aranea, Phalangi- 

 nm, Cyamus and Pagurus. Although I am unable to 

 come to any final deteimination on this curious and (if 

 it may be judged by the trouble it has given me) even ab- 

 struse point, yet I request the attention of entomologists 

 to the fact that one of the most singular characteristics of 

 the Pycnogonida is their possession of only one segment 

 to the abdomen ; in which they wholly diffisr from Pha- 

 langium, but agree with Aranea and Pagurus. Nay, 



