NOTES ON THE DEVELOPMENT OF THE ARANEINA. 689 



missures between the ganglia. My observations shew that for 

 the spider, at any rate, nothing of the kind is present. 



As shewn in the longitudinal section (PI. 32, fig. 21), the 

 ganglion of the chelicerae has now united with the supra-ceso- 

 phageal ganglion. It forms, as is shewn in fig. 20 b (ch. g.}, 

 a part of the oesophageal commissure, and there is no sub- 

 cesophageal commissure uniting the ganglia of the chelicerae, 

 but the cesophageal ring is completed below by the ganglia of 

 the pedipalpi (fig. 20 c,pd.g.}. 



The supra-cesophageal ganglia have become completely sepa- 

 rated from the epiblast. 



I have unfortunately not studied their constitution in the 

 adult, so that I cannot satisfactorily identify the parts which can 

 be made out at this stage. 



I distinguish, however, the following regions: 



(1) A central region containing the commissural part, and 

 continuous below with the ganglia of the chelicerae. 



(2) A dorsal region formed of two hemispherical lobes. 



(3) A ventral anterior region. 



The central region contains in its interior the commissural 

 portion, forming a punctiform, rounded mass in each ganglion. 

 A transverse commissure connects the two (vide fig. 20 b}. 



The dorsal hemispherical lobes are derived from the part 

 which, at the earlier stage, contained the semicircular grooves. 

 When the supra-cesophageal ganglia become separated from the 

 epidermis the cells lining these grooves become constricted off 

 with them, and form part of these ganglia. Two cavities are 

 thus formed in this part of the supra cesophageal ganglia. 

 These cavities become, for the most part, obliterated, but persist 

 at the outer side of the hemispherical lobes (figs. 20 a and 21). 



The ventral lobe of the brain is a large mass shewn in 

 longitudinal section in fig. 21. It lies immediately in front of 

 and almost in contact with the ganglia of the chelicerae. 



The two hemispherical lobes agree in position with the fungi- 

 form body (pilzhutformige Korperti), which has attracted so much 

 the attention of anatomists, in the supra-cesophageal ganglia of 

 Insects and Crustacea; but till the adult brain of Spiders has 

 been more fully studied it is not possible to state whether the 

 hemispherical lobes become fungi form bodies. 



