MORPHOLOGY OF BRAIN AND SENSE ORGANS OF LIMULUS. 53 



supply the median eyes, or " Hauptaugen ; " while the others, 

 irrespective of their position on the head of the adult, are 

 supplied by the posterior ganglion, or that on the third segment 

 of the cephalic lobes (fig. 61). 



The brain-lobes of the second and third segments gradually 

 become indistinguishable. In their place, in the adult, one 

 sees a pair of deeply stained lobes (c. h., fig. 61), which are 

 probably homologous with the cerebral hemispheres of 

 Limulus. 



B. The Mid-brain, — There can be no doubt whatever that 

 the whole of the cephalic lobes of the Scorpion are homo- 

 logous with the whole of the cephalic lobes of Acilius. The 

 next neuromere, that of the chelicerse, must be homologous 

 with the antennal neuromere of insects, because both bear 

 identical relations to the stomodaeal nerves. 



In Scorpions and Limulus there are four nerves connected 

 with the oesophagus. The most important are the lateral 

 stomodseal nerves, extending from about the middle of the 

 median margin of the cheliceral neuromere inwards along the 

 sides of the oesophagus (figs. 59 — 61, I. st. n.). What I 

 formerly regarded as the pre-oral cross-commissures of the 

 cheliceral neuromere (a. p. st.) I am now convinced is merely 

 the much shortened anterior pons stomodaei of insects. It is 

 composed at first of numerous ganglion-cells surrounding a 

 cortical " punct^^ substance, and in some Spiders, according to 

 St. Remy, contains in the centre a ganglionic enlargement 

 that I regard as the remnant of a frontal ganglion. The same 

 commissure, called by St. Remy " pons stomatogastique," 

 occurs in Myriapods (fig. 62, a. p. st.). It there strongly 

 resembles the anterior pons stomodaei of Arachnids, and yet 

 shows, by the presence of a distinct median ganglion, its 

 undoubted homology with the cross-arms of the frontal ganglion 

 of Insects (compare figs. 58 — 62). 



when applied to the embryos, have entirely different meanings from those 

 when applied to the adults. This is owing to the doubling of the cerebral 

 lobes on to the back of the adult, so that the anterior border of the cephalic 

 lobes becomes the posterior border. 



