MORPHOLOGY OF BRAIN AND SENSE ORGANS OF LIMULUS. 47 



B. The cephalic, sympathetic, or the stomodseal 

 nerves are very important landmarks in this region. The 

 anterior stomodseal, or "frontal " ganglion and its nerve arise 

 as a solid linear outgrowth from the median anterior wall of 

 the stomodseum. Its outer or proximal end is united by two 

 cross-arms with the lateral stomodEcal ganglia situated either 

 on the median border of the antennary neuromere, or on the 

 oesophageal commissures (PI. 5, fig. 57). This cross-commis- 

 sure I shall call the anterior pons stomodsei (a. p. st.). 

 In the later stages it is usually shaped like an elongated V, 

 owing to the fact that the frontal ganglion, which is situated 

 at the apex of the V, is carried a long distance inward by the 

 growth of the oesophagus. From the lateral stomodseal ganglia 

 the lateral stomodseal nerves extend inwards, one on either 

 side of the oesophagus (fig. 57, 1, n.). Their exact point of union 

 with the brain I have not been able to determine, because in the 

 forms that I have studied these nerves are either absent or im- 

 perfectly developed. However, from all I can gather about them 

 from the works of others, they must arise very near this point ; 

 moreover that is their point of origin in Scorpions and Limulus. 



The lateral and median stomodseal nerves expand at inter- 

 vals into ganglia united with one another by commissural 

 strands. These ganglia and strands are specially well developed 

 in lulus, as shown by Newport (fig. 62). 



The lab rum, which in Acilius I have shown to be un- 

 questionably a paired organ, arising from the very anterior 

 margin of the cephalic lobes, is innervated, strangely 

 enough, from the roots of the anterior pons stomo- 

 dasi, a condition which seems to prevail throughout the 

 Myriapods, Insects, Arachnids, and probably the Crustacea. 

 Moreover there appears to be present in a sufficient number 

 of cases to make it typical for the whole group of Insects a 

 small unpaired nerve directed outward and backward from the 

 frontal ganglion toward the labrum (tig. 53). It is obvious 

 that the innervation of the labrum is different from that of 

 any other Arthropod appendage, and I believe it has special 

 significance, as I shall presently indicate. 



