318 ME, H. M. BERNARD ON THE 



the labnmi and fused witli it, the two togetlier forming a beak. These modifications of 

 the 1st segment of the Arachnidan body (which have been again modified in the different 

 families) appear to me to be the essential characteristic of the class. 



Second Segment. — The 2nd segment carries the pedipalps, developed primarily as 

 sensory organs, as will be described in the section on the limbs. Dorsally this segment 

 is completely obscured by the cephalic lobes of the 1st segment ; indeed, nearly all that 

 remains of it is now comprised in the basal regions of the pedipalps and the cuticle 

 immediately surrounding them. 



Third Segment. — Passing to the 3rd segment, viz. that which carries the first pair of 

 ambulatory legs, we find, dorsally, portions of the tergite jirotruding from under the 

 cephalic lobes, while ventrally this segment is the smallest of the five segments com- 

 posing the under-surface of the cephalothorax. The limbs which it carries are, as 

 we shall see, in process of transformation from walking-legs with claws into a second 

 pair of sensory limbs. This segment is further interesting because the openings of the 

 coxal glands occur on it behind the coxse. 



In Phrynus and Thelyphonus we find the tendency to reduction and compression of this segment 

 carried still further; indeed, in the latter, neither the coxal joints of its limbs nor its sternum any 

 longer take part in the formation of the ventral surface. This compression of the 3rd segment is of 

 great morphological interest in connexion with the origin of the endosternite (see next page). 



Mil, 5th, and 6th Segments. — The following three segments are freely movable, a primi- 

 tive feature shared to some extent with Schlzoiwtus. Posterior to the coxae of the first 

 of these occur large stigmatic openings of the tracheal system, the significance of which 

 will be discussed in the section on Respiration. These segments carry the three posterior 

 pairs of limbs, which, in the Galeodidte, are those specialized for locomotion. 



The Abdominal Segments. — The segments themselves require but little further descrip- 

 tion. The 1st segment has a median genital aperture, covered by a pair of opercula 

 opening posteriorly and towards the median line. These ojjercitla, as will be shown 

 below, are the vestigial remains of vanished limbs. The 2nd and 3rd segments have 

 (also under opercula closely resembling those of the genital aperture) a pair of stigmatic 

 openings into tracheae. The stigmatic opercula in the genus Galeodes are armed 

 posteriorly with rows of short stout spines j)rojecting backward, " the stigmatic combs." 

 These serve, I think, princiijally to keeji the stigmatic apertures in communication with 

 the surrounding air, which would certainly be difficult when the abdomen is contracted. 

 In the genus Galeodes, the -Ith segment has a single median stigma, which, however, 

 is sometimes closed, although still connected with the tracheal system by a much 

 diminished tracheal tube. In Rhax, this median stigma has vanished altogether. 

 A study of the ventral surface leads almost irresistibly to the conclusion that the 

 three pairs of opercula on the first three segments were once followed by a complete 

 series which have vanished pi-ogressively from before backward. 



The anus opens, except in Rhax, through a terminal median slit stretching almost 

 completely across the anal papilla. 



