164 



DEVELOPMENT OF AMPHIOXUS. 



able to determine the precise origin of the longitudinal 

 nerve discovered by him. This nerve, which lies on either 

 side at the place where the ligamentum denticulatum 

 passes into the gelatinous lamella derived from the inter- 

 ccelic membrane, gives off the branches which form the 

 "branchial plexus." Van Wijhe states that the origin of 

 the " ramus branchialis vagi " of Amphioxus is to be 

 sought in the eighth to the tenth dorsal spinal nerves. 



Fig. 91. Anterior portion of young Ammoccetes of 4 mm., to show extension 

 of brain, origin of endostyle (thyroid), relations of branchial nerves, etc. (After 



KUPFFEK.) 



/, 11, III, IV. The so-called " Hauptganglia." / and //. Trigeminus. 

 ///. Acustico-facialis. IV. Glossopharyngeus. V. Vagus. 



au. Auditory capsule, ch. Notochord. e. Endostyle (hypobranchial groove, 

 thyroid), hy. Hypophysis, in front of which is the nasal groove, n.l. Nervus 

 lateralis. n.br. Nervus branchialis. o.p. Eye. /. Pineal body (epiphysis). 

 p.m. Prasoral endodermic pouch (median portion of praemandibular cavity. 

 st. Stomodceum. /, VIII. First and eighth gill-pouches; the small circles behind 

 the gill-pouches indicate the positions of the external openings of the gill-pouches, 

 which will become perforated later. The small black spots in front of the (later 

 appearing) external openings represent the so-called ganglia prcztrematica. 



He found that the nerve curved ventralwards in front and 

 passed downwards through the interccelic membrane until 

 it reached the level of the ventral transverse muscles in 

 front of the visceral branch of the eleventh spinal nerve. 

 He was unable to follow it further in the complex nerve- 

 plexus which lies on the surface of the muscles. It is 

 probable, however, that the branchial nerve arises from 



