46 MB. M. LAURIE ON THE 



of my view. Balfour* gives a very short account o£ this region, 

 and dees not say whether the stercoral pocket is formed from 

 the proctodseum or not ; and Morin gives no figures, and his 

 account is brief and inconclusive. The point at all events will 

 bear re-investigation. 



Coj^cLrrsiois". 



The ultimate summing-up of all morphological work is its 

 embodiment in a classification which shall express tlie true 

 relations of forms to each other. This I do not feel prepared to 

 do as regards the Arachnids ; but a few points may be touched 

 upon. I have elsewhere t given some reasons for dividing the 

 terrestrial forms into two subclasses similar to those suggested 

 by Pocock J, and for considering the Scorpions as more nearly 

 related to Limulus, and the rest of the Arachnids to the Eury- 

 pterids. A further argument may be found in the apparently 

 invariable presence of a coxal gland on the third appendage in 

 the latter section. The development of lung-books from branchiae 

 twice over would seem the chief difficulty in this view ; but if, as 

 I have tried to show, the first lung-books of Pedipalpi are equi- 

 valent to the pectin es of Scorpions, the same difficulty faces us if 

 we try the old hypothesis. 



The mutual relations of the forms constituting the second 

 subclass (termed by Pocock "Lipoctena") is not quite clear. That 

 the Arachnids and Pedipalpi are closely related is evidenced by 

 their possession of two pairs of respiratory organs, a stercoral 

 pocket, similar chelicerse, legs segmented in the same way, and a 

 not very different disposition of the eyes. Beyond these two the 

 different orders do not seem to show any very special relations to 

 each other, and one is met at the outset by the difficulty con- 

 cerning trachese. These are the common possession of the 

 Phalangidse, Spiders, Pseudoscorpions, and Galeodes That the 

 tracheae of Spiders have developed within the limits of that order 

 is, I think, indisputable, as the Tetrapneumones, or at all events 

 Liphistms, must be admitted as being the lower forms. But no 

 possible arrangement enables one to derive the Phalangidse, 

 Pseudoscorpions, and Galeodes from the Dipneumones without 

 violating every rule of morphological probability. It must be 



* Q. J. M. S. XX. 



t Trans. E. S. Edinb. vol. xsxvii. 



I Ann. & Mag. Nat. Hist. vol. xi. 



