16 Alexander Pelrimkevitch , 



,,Das Nervcnsystcm bcsteht auf diesem Stadium im Ccphalothorax 

 aus Ganglien, welche in ihrem Inneren deutliche, noch nicht ver- 

 schlossenc Hohlen aufweisen, und zwar aus dem unpaaren Nacken- 

 ganglion und einer Reihe von paarigen Ganglien: zwei Paaren 

 Schcitelganglien, zvvei Paaren Augenganglien (das eine fiir die seit- 

 lichen, das andere fur die mittleren Augen) dem paarigen Cheliceren- 

 ganglion, dem paarigen Pedipalpenganglion, vier Paaren Beinganglien 

 und einem paarigen Abdominalganglion ; im Hinterleibe dagegen 

 liegen drei Paare einzelner Ganglien und eine hintere gangliose Masse, 

 welche aus mehreren Ganglien zusammengesetzt ist" (S. 705). 



With other words We have one single and five paired ganglia which 

 will make up the brain of the adult spider and furnish the nerves 

 for the prae-oral segments. The single ganglion may be compared to 

 the ganglionic mass in the prostomium of Pol^^chetes but there seems 

 to be no good reason why the paired ganglia should not be considered 

 as forming five segments. Although Schimkewitsch does not men- 

 tion any ganglion for the rostrum (upper lip) the latter has been con- 

 sidered by Montgomery to represent in Theridium "a pair of true 

 prae-oral appendages, of which the rostral sacs constitute the coelom 

 and the cerebral ganglia the neuro meres." He based his idea of the 

 segmentation of the head on the number of coelomic sacs and of paired 

 appendages and came therefore to the conclusion that spiders have 

 only two prae-oral segments, the rostral (the first) and the cheli- 

 ceral (the second). This conception seems to me to contain an error 

 since the rostrum lies behind and not in front of the chelicera. On 

 examining my own sections through young Lycosas and adult Pholcus 

 I find that the pair of nerves supplying the rostrum arises behind the 

 nerves of the chelicera and represents the last pair of nerves given 

 off by the supraoesophageal ganglionic mass or brain. At present 

 I am, however, unable to state whether these rostral nerves arise 

 merely from the lower lobes of the paired ganglion of the chelicera or 

 have their own pair of ganglia. The neuromeres of the brain are Well 

 defined in young spiders, although of course not completely separated 

 as in embryonic stages. Do they represent separate segments ? It 

 is hard to say. A typical segment is usually composed of severa' 

 meroms such as sceletal plates, myomeres, coelomic sacs, neuromeres 

 and a pair of appendages. In different regions of the body any one 

 of these meroms may be entirely eliminated or fused with a correspon- 

 ding merom of the adjoining metamere and there seems to be no good 

 reason why neuromeres should not be as important as coelomic 

 meroms. We may therefore say that, while it is certain that post-oral 

 somites have occupied a prae-oral position, there is no sufficient evi- 



