No. I.] STUDIES ON LIMULUS. 1 33 



recently devoted some attention to the development and mor- 

 phology of the brain. 



Owen and Milne-Edwards gave a general plan of the distri- 

 bution of the larger nerves arising from the brain and ventral 

 cord, but did not agree upon the number of these nerves, and 

 left practically untouched the innervation of the heart, intes- 

 tine, and appendages. Packard and Viallanes confined their 

 investigations principally to the supra-oe^ophageal ganglion and 

 the nerves arising therefrom, and restricted the term " brain " 

 to this portion of the nervous system. 



Patten figured and described the entire circum-oesophageal col- 

 lar and ventral cord and applied the term "brain" to the whole 

 nerve ring. He furthermore divided the brain into four regions : 

 (i) the fore-brain, which comprises the cerebral lobes or supra- 

 oesophageal ganglion ; {2) the mid-brain, or cheliceral neuro- 

 mere ; (3) the hind-brain, or six thoracic neuromeres ; and (4) 

 the accessory brain, or chilarial and opercular neuromeres. In 

 the following description of the brain the nomenclature of 

 Dr. Patten will be followed. 



I. The Central Nervous System. 



The central nervous system may be divided into brain and 

 ventral cord, the former consisting of the fused ganglia of the 

 circum-oesophageal collar, and the latter of the abdominal 

 ganglia and their longitudinal connectives. 



As the primary object of this paper is to give a clear presen- 

 tation of the distribution of the peripheral nerves, the internal 

 structures of the central nervous system will not be discussed 

 further than is necessary in defining the origins of the various 

 nerves. 



a. The Brain. 



In the adult Limulus the brain (Pis. VI-VIII, and X, 

 Figs. 1-3, II, and 12) is nearly circular and fits snugly around 

 the oesophagus close to the mouth. It is included within a 

 vascular ring and is thus completely bathed in blood. At the 

 sides of the oesophagus there is a slight flexure, in a neural 



