98 PATTEN AND REDENBAUGH. [Vol. XVI. 



PAGE 



9. Fusion of muscles of different neuromeres accompanied by fusion of 



nerves supplying muscles 179 



10. Evidence that chilaria are not only distinct appendages, but resemble the 



abdominal rather than the thoracic appendages 179 



11. Innervation of liver, nephridia, and generative organs as yet unobserved 180 



INTRODUCTION. 



The senior author first began work on the nervous system 

 of Limulus in 1889, and after various interruptions the distribu- 

 tion of the more important nerves was worked out and recorded 

 in the shape of rough sketches and notes. Especial atten- 

 tion was given to the distribution of the haemal, cardiac, and 

 sympathetic nerves, with the hope of finding facts that might 

 point toward conditions similar to those in vertebrates. In 

 some respects these hopes were not realized, or at least 

 not in the particular ways looked for, while in others, con- 

 ditions were found that more than exceeded our expectations. 

 For example, a very careful search was made for lateral 

 line nerves similar to those in vertebrates. Various embryo- 

 logical data seemed to indicate that one might be found run- 

 ning parallel with and close to the free edge of the carapace 

 and abdomen, because in the embryos this area is early marked 

 out by a thickened band of ectoderm along which are scattered 

 a series of minute sense organs. Every attempt to find such a 

 nerve in that region both in the embryos and in the adult 

 failed. But a nerve was finally found on the neural surface 

 nearer the median line that fills some of the requirements of 

 a lateral line nerve (PI. VI, /«), for it is a purely sensory 

 cranial nerve extending at right angles to the course of the 

 other cranial and spinal nerves, nearly, if not quite, the whole 

 length of the head and trunk. It branches more freely in the 

 abdominal region and supplies the skin along its course, but the 

 exact nature of the sense organs to which its branches are dis- 

 tributed, and whether this nerve is split off originally from the 

 sensory thickening that runs round the embryo, and which 

 corresponds in position with the edge of the future carapace 

 and abdomen, could not be determined. The fact that it proba- 

 bly does not supply the line of marginal sense organs in the 



