423 



The nervous cord, as in the Acarina, is formed long before the 

 other internal systems of organs ; the development of the dorsal 

 vessel some time after succeeding that of the nervous cord, while 

 the alimentary canal is not formed until some time after the larva 

 is hatched. 



The next stage observed, and one of exceeding interest, was 

 studied in longitudinal sections of the larval Limulus. If we 

 make a longitudinal section of the young king crab when a 

 little over an inch long, the disposition of the cephalothoracic 

 portion of the cord is exactly as in the full-grown individuals. 

 The nervous ganglia are then united into a continuous nervous 

 collar surrounding the oesophagus, no ganglionic enlargements 

 being observed, the collar in fact consisting entirely of ganglia, 

 the commissures being obsolete ; in front of the oesophagus and 

 in the same plane as the oesophageal collar lies the supraoesopha- 

 geal-ganglion, or so-called brain ; not as usual in the normal Crus- 

 tacea, raised above the mouth into the roof of the head. On the 

 contrary, the oesophagus passes behind the brain and through the 

 collar at a right angle to the plane of the oesophageal collar and 

 '^liii taken collectively. Now a section of the larva before 

 moulting shows a most important and interesting difference us re- 

 gards the ganglia which supply nerves to the appendages of the 

 , '»'l»lia]"tliora\. These are entirely separate, the spaces between 

 them, where they are connected by commissures, being as wide as 

 the ganglia themselves are thick. Five ganglia were observed 

 corresponding to five anterior pairs of members. It is probably 

 not until after the first moult at least that the adult form of the. 

 nervous cord is attained. 



Some interesting questions in the morphology of Limulus arise 



of Limulus differs remarkably from that of the normal cnistacea, 

 i.e., the Decapods, in sending off no antennal nerves, but only 

 two pairs of optic nerves, there being in fact in Limulus no anten- 



system only resembles that of Limulus in the thoracic and cepha- 



