Vestigial Stigmata in the Arachnida. 



151 



sepiaris). There is great difference in the degree of distinct- 

 ness even among specimens of one and the same species. 

 The two figured were chosen at random ; others even more 

 distinct could doubtless be found. 



Fig. 1. 



Fia-. 2. 



Fisr. 3. 



ir 

 in 



VJT 



vm 



■J 



Fig. 1. — Abdomen of Thelyphonus manillanus, C. Koch, showing the 



stigmatic scars; the functional lung-books are marked by 



dotted lines. 

 Fig. 2. — Typopeltis Stimpsonii, Wood, showing the stigmatic scars along 



the posterior edges of definite areas. 

 Fig. 3. — Prionurus aiwtralis, Linn., showing the stigmata along the 



posterior edges of sharply defined areas. 



While the anterior and outer (lateral) edges of the areas 

 seem marked off more by change in the character of the 

 surface of the chitin, the inner and posterior edges, especially 

 the latter, are scar-like — often very pronounced scars 

 indeed. It will be seen from tig. 1 that these areas repeat 

 segmentally the positions (and the scars the apertures) of the 

 lung-books in the second and third segments. Any doubt as 

 to this seems to me to be set at rest by a comparison with 

 Scorpio, in which we have almost exactly similar areas with 

 stigmatic apertures along their posterior margins. Fig. 3 was 

 drawn from the scorpion which happened accidentally to be 

 nearest me on the table. Any scorpion will show similar 

 areas more or less distinctly. 



No one, I believe, doubts the homologies of the lung-books 

 of Scorpio and Thelyphonus. The areas with these scars on 

 segments V and VI of Thelyphonus must correspond with the 

 areas with their stigmata on segments V and VI of Scorpio. 

 If this reasoning is correct, Thelyphonus originally possessed 

 at least seven pairs of lung-books, five pairs of which have 

 now vanished. 



Counting the genital opercula, we have therefore in Thely- 

 phonus vestiges of eight pairs of abdominal limbs on the 

 first eight segments. 



