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HOWAKD AYERS 



terminalis. The smaller branch curves forward and downward 

 over the surface of the notochord and innervates the surface 

 territory about the anterior end of the buccal cavity as well as 

 the walls of the terminal pocket of the mouth and the dorsal 

 hypophysial organ which formerly occupied a surface position 

 as the preoral pit of the larva. 



The terminal territory of the Amphioxus body is thus a ter- 

 minal sensory organ. As far as known, the sensory elements are 

 isolated sensory cells distributed with some regularity of spacing 

 throughout the epithelial covering of the body in the territory 

 supplied by the terminal and septal nerves. These sensory cells 

 have not been found in other localities. They are innervated by 

 terminal twigs given off from the short fibrils which issue from 

 the groups of subepithelial ganglion cells belonging to these two 

 nerves (fig. 11). The close association of the terminal and septal 

 nerves in their peripheral distribution is reflected in the central 

 exchange of fibers (figs. 8, 9, and 10) and doubtless in their 

 physiological functions, to the extent of their being grouped to- 



ABBI^EVJATIONS 



A, place of origin of the hypophysial 

 organ 



B, last surface position of hypophysial 

 organ 



Br, brain. 



C, position of hypophysial organ in 

 adult 



G, nasal gland (Jacobson's) organ 



n, hypophysis 



HC, hypophysial canal 



h, hypophysial extension 



B..S., hypophysial sac 



h.O, lobus olfactorius 



l.t, lamina terminalis 



M, mouth 



M' , anterior buccal pouch 



AT, nose 



n, external nasal opening 



n./, nasal fold 



n.n, nasal nerve 



liC, nasal canal 



'NF, nasal fold 



A^.p, nasopalatine nerve 



0, olfactory nerve 



OL, L.O, olfactory lobe 



ON, olfactory nerve 



op, optic nerve 



P, anterior buccal pouch 



PN, prenasal sac 



SN, septalis 



Sk, cranial wall 



Sj), nasal septum 



S, hypophysial branch of septalis 



T, n. terminalis 



T.&S, n. terminalis and n. septalis 



TO, terminal organ 



TH, hypophysial branch of terminal 



nerve 

 tt, terminal nerve bundle 

 V, velum 

 V, valve 

 Vt, ventricle 



