GENERAL CONSIDERATIONS. 



157 



importance in a comparison with the former, while in comparing 

 the Pantopoda with the Arachnida the shape of the adult receives 

 more attention. It cannot be denied that the whole appearance of 

 the Pantopoda suggests a certain similarity to the Araneae. But 

 a nearer comparison at once reveals a difficulty, inasmuch as the 

 Pantopoda possess one pair of limbs more than the adult Arachnid. 

 An attempt has been made to overcome this difficulty by considering 

 the first two pairs of limbs of the Pantopoda (Fig. 74, 1 and 2) 

 as ecpuivalent to the chelicerae and the pedipalps of the Arachnida, 

 and the third to the sixth limb of the former as equal to the 

 ambulatory limbs of the latter (Fig. 74, 3-6). The ovigerous limbs 

 (Fig. 74, 3) would thus represent the first pair of ambulatory limbs 

 of the Arachnida, and the seventh limb would be the homologue of 



Fig. 74. — Male of Nymphon hispidum seen from the ventral side. The setae are omitted (after 

 Hoek, from Lang's Text-book). 1-7, limbs ; aft, abdomen ; s, proboscis. 



the first pair of abdominal limbs. In view of the fact that in the 

 Insecta an abdominal segment is separated from the posterior part 

 of the body, and may enter into the closest relation to the thorax, 

 such a view might be defended. Those Avho adopt it consider that 

 the addition of another pair of limbs to those already specialised 

 for locomotion was determined by the withdrawal of the third limb 

 from the ambulatory series for use in the care of the brood. 

 According to this view, the four pairs of ambulatory limbs of the 

 Pantopoda would not be homologous with those of the Arachnida. 

 The last homology must, however, be regarded as possible, and in 

 that case the loss of an anterior limb in the Arachnids would have 

 to be assumed. It has already been pointed out (p. Ill) that the 

 rostrum has been conjectured to represent a pair of limbs. 



