Mr. A. Tiilk on the Anatomij of Phalangium Opilio. 327 



lens behind the cornea, and thus indicating their great freedom of 

 connexion, if indeed any exist. The lateral pair of eyes are not 

 nearly so distinct and prominent as the above, and would appear 

 to be wanting altogether in certain species, as in a specimen of 

 P. quadridentatwn, I have been unable to perceive the slightest 

 traces of their existence. 



Respiratory System. — The respiratory organs of the Phalangia 

 consist of two large tracheal trunks (PI. V. tig. 33.), situated upon 

 either side of the cephalo-thoracic cavity. They commence from 

 two stigmata, which open externally between the posterior coxae 

 and under surface of the abdomen, and from thence they pass 

 inwards, forwards and slightly upwards, converging towards each 

 other at their anterior termination. In their course are several 

 slight dilatations, where large branches are given off. /From the 

 oblique position of the posterior coxae, these trunks have to 

 curve somewhat abruptly round their convexity, and owing to 

 the narrow space in which the spiracle lies, are compressed and 

 smaller in calibre at that particular point. Their different rela- 

 tions from behind forwards are as follows : — As they emerge from 

 beneath the posterior coxs they pass over a part of the ovarium, 

 which has been said on a former occasion to di]) deeply down 

 there upon either side, and are then situated for the remainder of 

 their course upon the inner extremities of the coxal joints resting 

 partly upon the muscles passing into these open cavities, while near 

 to their anterior extremities, they overlie the sides and crural 

 branches of the thoracic ganglion. These trunks are somewhat 

 remarkable for their large size and short course, and are readily 

 distinguished from other organs in dissection by their additional 

 pearly lustre.l The best mode of displaying them is to commence 

 from the dorsal surface of the animal by removing the heart and 

 all the digestive viscera, and in the female the ovarium and 

 ovisac. 



Fm'ther than their principal trunks, Straus-Durckheim *, in 

 his recent able work, states, " Je n^ai jamais pu m^assm-er de la 

 forme et de la disposition des trachees dans les Holetres." Tre- 

 viranus, however, long since described and figm'ed the respiratory 

 tubes and their branches, but as this excellent observer has done 

 so in a veiy general manner, it enables me, after much patient 

 re-investigation, to enter into more minute details. The primary 

 branches, also of considerable size, which proceed from each of 

 the main trunks, are about fom-teen in number, the majority of 

 which ramify among the \iscera of the thorax, while three only 

 upon either side are distributed to the abdomen. The first of 

 these abdominal air-tubes {at) is given off from the internal side 



* Traited'Anat. Comp., Paris 1842. 



