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anatomy and of the male accessory appendages of argus, 

 argyrognomon and other species for comparison, and of the 

 tibiae of these species showing how far they differed in the 

 so-called tibial spine. Commenting upon them, he said — 



" In examining the tibial spines of argus and argyrognomon 

 I found a curious reversion in oce specimen of argus from 

 Spain ; the tarsus is normally (in the $) in one piece, all the 

 joints and terminal claw being fused together without trace of 

 articulation. The first Spanish specimen I examined had the 

 tarsus, howevei-, divided into three joints. I wondered, of 

 course, whether this might be a character of the Spanish races, 

 but I failed to find another such specimen, the Spanish 

 and others absolutely agreeing. There is an ambiguity in 

 calling this a tibial spine, it is the extremity of the tibia itself. 

 What is usually called the tibial spine is a separate process 

 not present in these species. 



" The comb-like end of the clasp of P. argus presents greater 

 variation than one would quite expect, the total number of 

 teeth varying within considerable limits, and the presence or 

 absence of one or several minor or ill-developed teeth at either 

 end of the series is another point in which there is great 

 inequality in different specimens. The opposite clasps of one 

 individual differ very frequently, and a different number of 

 teeth to the comb may be found in specimens from one locality. 

 There is probably also some geographical variation, but this I 

 have not demonstrated. 



"We may conclude that considerable differences in this 

 portion of the clasp do not interfere with complete syngamy 

 in the species. The tendency to variation is obviously suffi- 

 ciently strong easily to establish a new species, if a section of 

 the present species could be segregated for no very long time. 

 We may also conclude that these special and formidable pro- 

 cesses do not correspond with any portion of the female 

 appendages similarly differentiated, else four prongs to the 

 comb would not be equally useful with five, six, seven, or eight. 



" The great difference between the genitalia of argus and 

 axgyrognomon has suggested to me the question as to whether 

 these two species are really so closely related as we suppose. 

 It is open to us to believe that they are from different portions 



