103 F. M. BALFOUR. 



(3) A ventral anterior region. 



The central region contains in its interior the commis- 

 sural portion, forming a punctiform rounded mass in each 

 ganglion : a transverse commissure connects the two masses 

 {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-oesophageal ganglia become sepa- 

 rated from the epidermis the cells lining these grooves 

 become constricted oif with them, and form part of these 

 ganglia. Two cavities are thus formed in this part of the 

 supra-oesophageal 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 shown in long 

 section in fig. 21. It lies immediately in front of and almost 

 in contact with the ganglia of the cheliceree. 



The two hemispherical lobes agree in position with the 

 fungiform body (pilzhutformige Korpern), which has attracted 

 so much the attention of anatomists, in the supra-oesophageal 

 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 the fungiform bodies. 



Hatschek^ has described a special epiblastic invagination 

 in the supra-oesophageal ganglion of Bombyx, which is pro- 

 bably identical with the semicircular groove of Spiders and 

 Scorpions, but in the figure he gives the groove does not 

 resemble that in the Arachnida. A similar groove is found 

 in Peripatus, and there forms, as I have found, a large part 

 of the supra-cesophageal ganglia. It is figured by Moseley, 

 ' Phil. Trans.,' vol. 164, pi. Ixxv, fig. 9. 



The stomodseum is considerably larger than in the last 

 stage, and is lined by a cuticle ; it is a blind tube, the blind 

 end of which is the suctorial pouch of the adult. To this 

 pouch are attached the vertical dorsal, and two lateral muscles 

 spoken of above. 



The proctodaeum (pr.)has also grown in length, and the two 

 Malpighian vessels which grow out from its blind extremity 

 (fig. 20 e, mp. g.) have become quite distinct. The part now 

 formed is the rectum of the adult. The proctodaeum is sur- 

 rounded by a great mass of splanchnic mesoblast. The mesen- 

 teron has as yet hardly commenced to be developed. There 

 is, however, a short tube close to the proctodaeum (fig. 20 e^ 

 me^), which would seem to be the commencement of it. It 



* *' Beitrage z. Eutwick d. Lepidopteren," ' JenaiscLe Zeit.,' vol. xi, 

 p. 124. 



