434 PSEUDOSCORPIONID^E. 



nerve cords are distinctly differentiated and ganglionated. In 

 the embryonic state there is one ganglion for each segment. 

 The ganglion in the first segment (that bearing the chelicerae) is 

 very small, but is undoubtedly post-oral. 



At this stage, by a growth in which all the three germinal 

 layers have a share, the yolk is completely closed in by the 

 blastoderm. It is a remarkable fact with only few parallels, and 

 those amongst the Arthropoda, that the blastopore, or point 

 where the embryonic membranes meet in closing in the yolk, is 

 situated on the dorsal surface of the embryo. 



The general relations of the embryo at about this stage are 

 shewn in fig. 195, where the embryo enclosed in its double 

 cellular membrane is seen in a side view. This embryo is about 

 the same age as that seen from the ventral surface in fig. 196 A. 



The general nature of the further changes may easily be 

 gathered from an inspection of fig. 196 B and C, but a few 

 points may be noted. 



An upper lip or labrum is formed as an unpaired organ in 

 the line between the procephalic lobes. The pedipalpi become 

 chelate before becoming jointed, and the chelicerae also early 

 acquire their characteristic form. Rudimentary appendages 

 appear on the six segments behind the ambulatory legs, five of 

 which are distinctly shewn in fig. 195 ; they persist only on the 

 second segment, where they appear to form the comb-like 

 organs or pectines. The last abdominal segment, i.e. that next 

 the tail, is without provisional appendages. The embryonic tail 

 is divided into six segments including the telson (fig. 196 C, ab}. 

 The lungs (st) are formed by paired invaginations, the walls of 

 which subsequently become plicated, on the four last segments 

 which bear rudimentary limbs, and simultaneously with the 

 disappearance of the rudimentary limbs. 



Pseudoscorpionidae. The development of Chelifer has been in- 

 vestigated by Metschnikoff (436), and although (except that it is provided 

 with tracheae instead of pulmonary sacks) it might be supposed to be closely 

 related to Scorpio, yet in its development is strikingly different. 



The eggs after being laid are carried by the female attached to the first 

 segment of the abdomen. The segmentation (vide p. 93) is intermediate 

 between the types of complete and superficial segmentation. The ovum, 

 mainly formed of food-yolk, divides into two, four, and eight equal segments 



