PLATE 4. 



All figures, except 15a, from methylene-blue preparations. 



Figure 15. Branchiostoma lanceolatum. The fan-like branches of an 

 ascending visceral ramus of a dorsal nerve, viewed from the 

 interior. The visceral ramus reaches the internal surface of 

 the side muscles at a. The branches at c and d anastomose 

 with tho.se of adjoining ascending visceral rami. The branch 

 at e bends toward the exterior. The branches at h are bent 

 away from the muscle, i. e. toward the median plane of the 

 animal. X 93. 



Figure 15a. Diagram of part of a cross section of an Amphioxus, to show the 

 course of a dorsal nerve and its branches. 



Figure 16. B. lanceolatum. View of the inner (median, or atrial) face of 

 the lateral muscles of right side (lower half of figure), and of 

 outer (atrial) surface of the branchial wall (/>. u'.), cut ventrally 

 and turned up (the upper half of figure). To show branches 

 of an ascending visceral ramus passing to the pharynx. Por- 

 tions of the ligamentum denticulatum are marked I. d. The 

 plexus formed by the fan-like branches of an ascending vis- 

 ceral ramus is also shown. X S4. 



Figure 17. B. lanceolatum. Similar view to that of Figure 16. Nerves 

 entering the pharynx from the ligamentum denticulatum, 

 and a portion of the plexus of the latter structure. The 

 plexus in the " pocket " portions of the ligament is shown at pi. 

 d. The plexus of a primary branchial bar is marked h. p. 1, 

 and that of a secondary bar, b. p. 2. X 177. 



Figure 18. Branchiostoma caribaeum. Anterior is up. A part of the outer 

 plexus of the mouth border, on the right side of the body. X 93. 



Figure 19. B. lanceolatum. Plexuses on a primary bar, a secondary bar, 

 and a cross-bar of the pharynx, with nerve cells, c, c, in con- 

 nection. This is a view of the exterior surface of a part of 

 the pharj'nx which is near its ventral surface and near the 

 anterior end of the body on the right side; a, and h, have the 

 same meaning as in the following figure. X 254. 



Figure 20. B. lanceolatum. A view of the dorsal border of a portion of the 

 left side of the pharynx from the interior of the latter, showing 

 a nerve plexus. The primary bars are marked a, a, and the 

 secondary bar, b. X 254. 



Figure 21. B. lanceolatum. A nerve cell on the external side of a secondary 

 bar of the pharynx. The view is from the right side of the 

 latter, near the anterior end of the body. X 700. 



