The Development of Theridium. 341 



cheliceral ganglia push forward to add themselves to the brain, im- 

 mediately bounding the stomodaeum dorso-laterally and thus forming 

 the oesophageal commissures. The rostrum does not appear to pos- 

 sess separate ganglia. At the stage of reversion the neuropile is 

 developing, though still small in amount. At this stage also the 

 antero-median eyes arise as ectoblastic invaginations above the ros- 

 trum. 



Claparede described late stages of the eye development. Salensky 

 (1871) was the first to describe carefully the nervous system; he 

 found the semicircular grooves (foveae) of the cephalic lobes, found 

 the cerebral ganglia to arise by invagination of these lobes, and saw 

 eight pairs of ganglia develop in the cephalothorax from the ecto- 

 blast, but none in the abdomen. Balfour (1880) described correctly 

 the origin of the nerve ganglia from the ectoblast, in abdomen and 

 cephalothorax, found the cheliceral ganglia arise "quite independent 

 of the procephalic lobes," and observed that the greater part of the 

 latter "is destined to give rise to the supra-oesophageal ganglia." On 

 the anterior border of each procephalic lobe he distinguished a trans- 

 verse "semicircular groove." He showed that at reversion of the 

 embryo the cheliceral ganglia became part of the oesophagaeal com- 

 missures, and that the abdominal ganglia fuse together. Locy (1886) 

 confirmed Balfour's results, and added to it a full description of the 

 development of the eyes. Morin (1887) saw on the cephalic lobes 

 two semicircular grooves which close, sink below the ectoblast and 

 "join with the brain." Bruce (1887) described folds on the head 

 lobe which he called "amniotic folds" ; his figures show clearly that 

 he was describing the lateral vesicles. Schimkewitsch (1887) held 

 the cheliceral ganglia of Balfour to be the basal joint of the che- 

 licera and stated (erroneously) that none of the cephalothoracal 

 ganglia can be seen on surface views. He gave a detailed description 

 of the nervous system; twelve abdominal ganglion pairs develop in 

 PJwlcus; a separate ganglion pair for the rostrum, and in the abdo- 

 men a median ganglionic thickening besides the lateral ones. Schim- 

 kewitsch then made an extended comparison of the nervous system 

 with that of other groups. Kishinouye (1890, 1894) found the 

 semicircular gi-ooves of Balfour, called the part of the cephalic lobe 



