6 Mr. "R. T. Pocock on the 



the ' Encyclopaedia Britannica ; ' but it is difficult to find 

 grounds to justify this classification. 



In the form of the cephalothoracic appendages, especially 

 of the second pair, there is certainly a close similarity between 

 the Scorpions and the Pseudoscorpiones ; but in the structure 

 of the abdomen the difference between the two groups is 

 very great. But the same cannot be said of the abdomen of 

 the Pedipalpi and the animals now under discussion ; for the 

 two groups resemble each other in the absence of the pectines 

 and in the presence of only two pairs of respiratory stigmata. 

 Moreover, in such a form as Gurypus litoralis the same 

 number of somites can be made out in the abdomen as are 

 seen in this region in the Pedipalpi, namely twelve. Further- 

 more, there is the same inequality in the number between the 

 tergites and sternites, the former being one in excess of the 

 latter *. From the posterior somite forwards the dorsal and 

 ventral scleritcs correspond plate for plate until the third 

 tergite and second sternite are reached. Here the corre- 

 spondence ceases, there being but a single genital sternite for 

 the tirst and second tergites, exactly as in the Pedipalpi. 

 The stigmata are situated in tlie third and fourth abdominal 

 somites, but they have taken up a more lateral position than 

 in the Pedipalpi. 



In some other forms of this group one of tlie tergites has 

 disappeared, so that the abdomen is described by systematists 

 as being furnished with only ten of these plates. Moreover 

 the sterna similarly may be reduced to nine. 



So far as the embryological history of these animals is 

 concerned, it is especially interesting to note the presence of 

 four pairs of provisional aj)pendages attached to four of the 

 anterior segments of the abdomen. In the absence of evidence 

 to the contrary it seems justifiable to conclude that these 

 appendages are the exact homologues of the four pairs seen in 

 the Araneaj, a group which we have seen to be apparently 

 nearly related to the Pedipalpi. 



The next group to be considered is the Opiliones. The 

 animals of this order agree with the Pseudoscorpiones in the 

 tracheal nature of tlieir respiratory organs and in the absence 

 of a "waist" between the cephalothorax and abdomen. This 

 last featm-c has led to very remarkable results in the forward 

 migration of the generative aperture between the coxaj of the 

 posterior limbsj in some forms even to a position just behind 



• The last somite hax uot, so far a^ I am awavL', been previously recog- 

 nized as such. It is, except in distended specimens, almost entirely con- 

 cealed inside what is appjirently the last, namely the eleventh, bnt wliich 

 is in reality the la.<;t but one. 



