690 NOTES ON THE DEVELOPMENT OF THE ARANEINA. 



Hatschek 1 has described a special epiblastic invagination in 

 the supra-cesophageal ganglion of Bombyx, which is probably 

 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-ceso- 

 phageal ganglia. It is figured by Moseley, Phil. Trans., Vol. 

 CLXIV. pi. Ixxv, fig. 9. 



The stomodaeum 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 protodaeum (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. 

 mes], which would seem to be the commencement of it. It 

 ends blindly on the side adjoining the rectum, but is open an- 

 teriorly towards the yolk, and there can be very little doubt that 

 it owes its origin to cells derived from the yolk. On its outer 

 surface is a layer of mesoblast. 



From the condition of the mesenteron at this stage there 

 can be but little doubt that it will be formed, not on the surface, 

 but in the interior of the yolk, I failed to find any trace of an 

 anterior part of the mesenteron adjoining the stomodaeum. In 

 the posterior part of the thorax (vide fig. 20 d], there is un- 

 doubtedly no trace of the alimentary tract. 



The presence of this rudiment shews that Barrois is mis- 

 taken in supposing that the alimentary canal is formed entirely 

 from the stomodaeum and proctodaeum, which are stated by him 

 to grow towards each other, and to meet at the junction of the 

 thorax and abdomen. My own impression is that the stomo- 

 daeum and proctoda;um have reached their full extension at the 



1 " Ik-itiagc z. Entwick. d. Lepidopteren," JenaischeZeit. t Vol. xi. p. 124. 



