48 WILLIAM PATTEN. 



The lateral stomodaeal gauglia are usually situated on the 

 posterior median margin of the autennal neuromere, or some- 

 times on the oesophageal commissures. They are always united 

 with one another by a large transverse commissure that con- 

 tains, unlike the other post-oral commissures, many ganglion- 

 cells. In the young stages of Acilius (see ' Eyes of Acilius/ 

 fig. 44) I have figured a segment of the median sympathetic 

 nerve which seems to be united with this commissure to form 

 a rudimentary ganglion, and in the fourth larval stage of the 

 lobster I have found a very distinct ganglion in the middle of 

 this commissure. No doubt this commissure is characteristic 

 of the whole group of Arthropods ; it is well known in Myria- 

 pods, Insects, and Crustacea, and I have found it in Limulus. 

 Its apparent absence in the Arachnids is probably due to the 

 crowding together of the neuromeres in the mouth region. 

 This commissure, I am convinced, also belongs to 

 the cephalic sympathetic system; but it may per- 

 haps contain fibres representing the cross-com- 

 missures of the antennal neuromere. I shall call 

 it the posterior pons stomodaei. 



Besides these nerves, most insects, as shown in the diagram- 

 matic fig. 53, are provided with a system of trunk-sympathetics 

 consisting of a chain of lateral and median sympathetic 

 ganglia ; the latter, as I have shown elsewhere, is derived from 

 the '' Mittelstrang ■"' of Hatschek, and probably terminates 

 anteriorly in the posterior pons stomodaei. 



c. The Convex Eyes and their Ganglia. — The convex 

 eyes form such an important part of the brain of Insects that it 

 is of great importance to determine exactly where they belong. 

 They are apparently so intimately associated with the fore- 

 brain that there seems little reason to doubt their derivation 

 from the cephalic lobes. But there are strong reasons for 

 supposing that they belong, not to the cephalic lobes proper, 

 but to the trunk, probably to the mid-brain neuromere. 



That they did not belong to the cephalic lobes originally is 

 indicated by the fact that in Acilius not a trace of them appears 



