338 



Proceeding-i of the Royo.l Irkh Academy. 



specialization in the secondary sexual organs may be seen in tlie four 

 types just mentioned ; tlie copulatory apparatus on the male's palp is 

 far more complex in the tivo-lunged than in the four-lunged spiders, 

 in' Anyphcena than in Dysdera, in Epeira than in Anyphaena 

 (fig. 4, a, b, c, d). Again, therefore, we are forced to the conclusion 

 that, among the Arachnida, tracheal tubes are derivable from lung- 

 books — and not lung-books from tracheal -tubes. And palaeontological 

 evidence confirms, so far as it goes, the teaching of morphology on 

 this question. For remains of Scorpions occur in the Silurian rocks, 

 of Pedipalpi and Avicularif orm Spiders in Carboniferous ; ^hile the 

 Dipneumonous Spiders, Phalangids, and Mites are not certainly known 

 until the Eocene. Therefore, without supposing that Spiders are 

 actually derivable from Pedipalpi, or these from Scoipions — each 



Fig. 4. Ventral view of the abdomen in four spiders. A, Aviculaira (nat. size) ; 

 B, Dysdera x 2 ; C, Anyphaena, x 3 ; D, Epeira, x 2 ; S^, S^, air-open- 

 ings. Also terminal portion of palps of the male in the same four 

 genera, a, Avicularia, x 2 ; b, Dysdera, x 3 ; c, Anyphaena, x 8 ; rf. 

 Epeira, x 8 ; to show increase in complexity of the copulatory organ. 



order having of course undergone specialization along its own lines 

 (the Scorpion's post-abdomen, for examjjle) — we are fully justified in 

 placing the origin of the Scorpions lower on the Arachnid stem than 

 we place the origin of the Pedipalpi, and that lower than the origin 

 of the Spiders. 



Embryological researches also support strongly the view just set 

 forth. The development of Spiders' lungs has been recently studied 

 by Simmons ('94) and Purcell ('95), and there can be no doubt from 

 their observations that the respiratory plates arise as outgrowths from 



