44 2 ARANEINA. 



the chelicera^, like the succeeding segments, is provided with 

 ganglia ; and that the ganglia of the chelicerae are quite distinct 

 from the supra-cesophageal ganglia derived from the procephalic 

 lobes. (3) The pointed form of the caudal lobe. In Pholcus 

 (Claparede, No. 442) the caudal lobe forms a projecting structure 

 which, like the caudal lobe of the Scorpion, bends forward so as 

 to face the ventral surface of the part of the body immediately 

 in front. In most Spiders such a projecting caudal lobe is not 

 found. While the embryo still retains its dorsal flexure con- 

 siderable changes are effected in its general constitution. The 

 appendages (fig. 200 D and E) become imperfectly jointed, and 

 grow inwards so as to approach each other in the middle line. 

 Even in the stage before this, the ventral integument between 

 the rudiments of the ganglia had become very much thinner, 

 and had in this way divided the ventral plate into two halves. 

 At the present stage the two halves of the ventral plate are still 

 further separated, and there is a wide space on the ventral side 

 only covered by a delicate layer of epiblast. This is shewn in 

 surface view (fig. 200 D) and in section in fig. 203 C. 



The stomodaeum (st) is much more conspicuous, and is 

 bounded in front by a prominent upper lip, and by a less 

 marked lip behind. The upper lip becomes less conspicuous in 

 later stages, and is perhaps to be compared with the provisional 

 upper lip of Chelifer. Each procephalic lobe is now marked by 

 a deep semicircular groove. 



The next period in the development is characterised by the 

 gradual change in the flexure of the embryo from a dorsal to a 

 ventral one ; accompanied by the division of the body into an 

 abdomen and cephalo-thorax, and the gradual assumption of the 

 adult characters. 



The change in the flexure of the embryo is caused by the 

 elongation of the dorsal region, which has hitherto been hardly 

 developed. Such an elongation increases the space on the 

 dorsal surface between the procephalic and caudal regions, and 

 therefore necessarily separates the caudal and procephalic lobes ; 

 but, since the ventral plate does not become shortened in the 

 process, and the embryo cannot straighten itself in the egg-shell, 

 it necessarily becomes ventrally flexed. 



If there were but little food yolk this flexure would naturally 



