SOLIFUGAE. 35 



part of the body. The broad and flattened cephalo-thorax seems 

 closely pressed against the ventral surface of the abdomen. The 

 rudiments of the limbs are seen on the cephalo-thorax ; the chelicerae 

 are bent towards the rostrum (Fig. 18, .4), the latter being approxi- 

 mated to the slit-like anal aperture. 



After the embryo is hatched, the abdomen appears longer, and 

 shows a few slight constrictions, which no doubt correspond to seg- 

 ments (Fig. 18, B). It carries two rows of dorsal setae, six in each 

 row. These are the only traces of the hairy covering which is so 

 profuse in the adult. The chitinous integument of the young is thus 

 only provisional. The young probably remain for some time after 

 hatching in a pupa-like condition, resembling in this respect the 

 Araneae (p. 58), which after leaving the egg remain quiescent 

 surrounded by a cuticular envelope, which is not cast off for some 

 time. This fact explains why the limbs (now bent backwards) up to 

 this time show no traces of segmentation (Fig. 18, B, Croxeberg), 

 and are also devoid of claws. No abdominal limbs were found in the 

 young animal, nor was their presence to be expected at so late a stage. 



A very remarkable structure, not occurring in the adult,* is a pair 

 of wing-like appendages, which arise dorsally between the points of 

 insertion of the first and second pairs of limbs. These outgrowths 

 consist of a double layer of cells, invested with a cuticle, and thus 

 represent integumental folds ; no nerves or tracheae extend into 

 them, and they are also devoid of muscles. 



The significance of these wing-like appendages is not understood. Croxeberg 

 compares them to the paired appendages of the Asellus embryo (Vol. ii., p. 151), 

 which are to be regarded as vestiges of the shell, but laj-s no special stress 

 on this comparison. t 



The Solifugae are distinguished from the other Arachnida by a few 

 important features, in which they seem more nearly to approach the 

 Insecta. The most anterior pair of limbs with the segment to which 

 it belongs enters into close relation with the preceding (cephalic) 

 segments, and is marked off from the posterior (thoracic) segments, 

 so that a separate cephalic region with three pairs of limbs arises. 

 This has been compared to the head of the Insecta and the next 

 region, which now consists only of three segments, each with a pair 

 of limbs, to the thorax of the Insecta. The resemblance is increased 



* Croxebekg examined adults of the same species, and found that this 

 structure was altogether wanting in them. 



t [It is now generally agreed that these structures are embryonic sensory 

 organs, and similar to those found in Phrynus. See Bruce (Lit. on Pedipalpi, 

 26) and Laurie (App. to Lit. on Pedipalpi, No. I.).— Ed.] 



