No. I.] STUDIES ON LIMULUS. 93 



5. The Circulatory System. 



a. The Heart. pagb 

 Location, general appearance, and size ; functional and rudimentary 



ostia; pericardial sinus and pericardium 126 



" Alary muscles " and other supports for the heart ; branchio-cardiac 



canals 127 



Arteries arising from the heart ; aortic arches and frontal artery, aortic 



valve, lateral arteries; valves of the ostia 128 



Histology of the Heart. 



Longitudinal connective-tissue fibers, basement membrane, internal layer 



of anastomosing muscle fibers, and longitudinal nerves 129 



b. Arterial System. 



The frontal and marginal arteries; the aortic arches 129 



Vascular ring enclosing brain 130 



Ventral artery and branches anastomosing with the superior abdominal 



artery 130 



Lateral arteries, variation, and occasional occurrence of a fifth lateral 



artery 130 



The collateral arteries ; hepatic and marginal arteries ; superior abdomi- 

 nal artery 131 



C. Venous System. 



Venous-collecting sinuses 131 



Branchio-cardiac canals 131 



Pericardial sinus 131 



6. The Excretory System. 



Nephridia, or brick-red glands 132 



7- The Reproductive System. 



Modification of second pair of chelae in male ; ovaries and testes ; 

 genital papillae 132 



II. The Nervous System. 



The work of Owen, Milne-Edwards, Packard, Viallanes, and Patten 



upon the nervous system 132 



The Central Nervous System. 

 a. The Brain. 



Circum-oesophageal collar; general appearance 133 



(i) The Fore-Brain. 



General form ; nerves arising from it 134 



(2) The Mid-Brain, or Tween-Brain. 



Consists of cheliceral neuromere 134 



Elements of a typical neuromere 134 



Neural or cheliceral nerves 134 



Haemal or lateral nerves 134 



Preoral commissure and rostral nerves 135 



Stomodaeal nerves 135 



