BRANCHIAL SENSE OEGANS OP ICHTHYOPSIDA. 223 



Fig. 40. High-power view of part of preceding section, showing lateral 

 line forming (l.l.), indifferent epiblast (i.e.) being pushed 

 away, and lateral nerve (l.n.) splitting off from thickening. 

 me. Mesoblast. T. ocellata. Camera luc. 



Fig. 41. Later stage of lateral line. Further back in trunk. High- 

 power, camera lucida. Shows same things as preceding 

 drawing. T. ocellata. 



Fig. 42. Drawing combined under camera from several horizontal 

 sections of an Elasmobranch embryo. Shows several cra- 

 nial ganglia fused with their branchial sense organs, p.br.o. 

 Primitive branchial sense organ, m.hr. Mid-brain, c.gl. 

 Ciliary ganglion. G.gl. Gasserian ganglion, f.gl. Facial 

 ganglion, au.gl. Auditory ganglion, gl.gl. Glossopharyn- 

 geal ganglion, vg.gl. I. First vagus ganglion, vg.gl.c. 

 Second, third, and fourth vagus ganglion, l.l. Lateral 

 line. l.n. Lateral nerve, au. Ear. n. Notochord. sp.c. 

 Spinal cord. 



Fig. 43. Diagrammatic horizontal section through the various bran- 

 chial sense organs and their ganglia. The reader should 

 conclude nothing from the cerebral vesicles figured here : 

 there is probably at least one between the trigeminal and 

 seventh nerves, and it is not figured here. 



Fig. 44. Part of a horizontal section of a six week's old salmon. 

 Shows the position and segmental arrangement of the 

 branchial sense organs (hr.o.) in the trunk, as, Intra- 

 muscular septa, n. Notochord. me. Mesoblast. 



Fig. 45. Diagram of lateral view of an Elasmobranch embryo. Shows 

 the central nervous system as plate not yet involuted, the 

 posterior roots of the cranial nerves (p.r.) the branchial 

 sense organs, the dorsal eye (oc), mouth, and gill-clefts. 

 Letters as before. 



Fig. 46. Similar diagram, to show the branches of nerves to gill-clefts. 

 The aborted branches in dotted lines. Also shows for- 

 mation and direction of various supra-branchial nerves 

 (s.b.n.). Vagus represented as supplying in all five clefts. 

 This figure is a more diagrammatic view of fig. 51, which 

 represents nature more or less accurately. 



Fig. 47. Horizontal section of a Torpedo embryo, showing rudiment 

 (cl. vi) of a sixth true branchial cleft. 



