nerve root passed behind (caudal to) the myotome of the segment to which it belongs.

C. Various shiftings of organs have taken place, due to (1) the expansion of the branchial apparatus and (2) the formation of a rigid cranium with the consequent loss of dorsal musculature. The shifting which may be observed during the ontogeny is a valuable source of information which should be further studied.

d. Largely on account of the peculiar relations with the ear, the nerve roots connected with the medulla oblongata have shifted backward during the phylogeny, and have left two neuromeres without nerve roots.

e. As a result of the expansion of the branchial apparatus the visceral sensory and motor components of the nerves caudal to the glossopharyngeus have been collected into a common root, the vagus. The somatic sensory and motor components of more or fewer of these nerves are present as rudimentary or complete dorsal and ventral roots which occupy the position of the original nerves. The number of these nerves retained depends upon the reduction of myotomes and cutaneous area in the postauditory region. In cyclostomes all the general cutaneous roots are present and independent; two of the somatic motor roots have disappeared. In gnathostomes, owing to the shifting backward of the vagus root at its attachment to the brain, the general cutaneous root following it has been absorbed and appears in the adult as the second r. auricularis vagi.

f. There has been no shifting forward of spinal nerves into the oblongata.

6. The typical sense organs of vertebrates fall into two categories: the neuromast organs constituting the acustico-lateral system, and the end buds or taste buds. These two sets of organs are absolutely distinct in structure, function, innervation, and central nerve relations.

7. It has previously been shown that the acustico-lateral system was derived from the general cutaneous. It is thought that the neuromast organs appeared first in a marginal portion

of the primitive neural plate. The material used in the formation of these organs was a portion of that part of the neural crest which gave rise to the general cutaneous component. The neuromast area was largest in the region of the VII nerve and neuromere vii, but extended forward probably one or two segments. It can not be exactly compared with the dorsal rami. It is thought that this area, together with the cutaneous ganglion cells, remained outside the neural tube and that later the ganglion cells migrated into the space between the ectoderm and neural tube. This is repeated in the ontogeny in the phenomena of the dorso-lateral placodes and the formation of ganglia from them.

8. The visual organs are thought to have been derived from the neural crest area also, in segments 2, 3 and 4. The retina of the lateral eye is supposed to contain the equivalent of a general cutaneous ganglion and its primary brain center. The optic tract is homologous with the internal arcuate fibers which arise from the cutaneous centers, decussate in the base of the brain and run to the tectum opticum. The epiphyses are thought of as modified general cutaneous ganglia whose centers have remained in the brain.

9. The olfactory organ is regarded as a special collection of sense cells of the invertebrate type, sensitive to chemical stimuli, which are gathered above the hypophysial opening as the organs of the same type in the invertebrate are gathered in the roof of the mouth and on the prostomium.

IO. On account of the similarity of their function it is expected that some morphological relation will be found between the olfactory and gustatory organs. The source of the end buds, the origin and history of the nerve components which innervate them, and the course of the gustatory paths in the brain constitute one of the most important problems in vertebrate morphology.

II. It is important that the origin of each of the sensory components in the cranial nerves should be fully worked out in at least a few forms. The cells which enter the ganglia from the neural crest and from the placodes should be traced con

tinuously until their fate is determined. The cells derived from the neural crest should be distinguished into general cutaneous, general visceral, or others as the result might be.

Naples, October 25, 1904.

LIST OF PAPERS CITED.

For numerous other papers see the literature lists in Nos. 35 and 70. Ahlborn.

Allis.

1. Untersuchungen über das Gehirn der Petromyzonten. Zeit. f. wiss. Zool., Bd. 39, 191-294. 1883.

2.

Ueber den Ursprung und Austritt der Hirnnerven von Petromyzon.
Zeit. f. wiss. Zool., Bd. 40, 286-308. 1884.

3. The Cranial Muscles and Cranial and First Spinal Nerves of Amia calva. Jour. Morph., Vol. 12, 487-808. 1897.

4. The Lateral Sensory Canals, the Eye-Muscles, and the Peripheral Distribution of certain of the Cranial Nerves of Mustelus laevis. Quart. Jour. Micr. Sci., Vol. 45 N. S., 87-236. 1901.

5. On Certain Features of the Lateral Canals and Cranial Bones of Polyodon folium. Zool. Jahrb., Abth. f. Anat. u. Ontog., Bd. 17, No. 4. 1903.

Beckwith.

6. The Early History of the Lateral Line and Auditory Anlages of Amia. Abstract. Science, N. S., Vol. 15, 575. 1902.

Bigelow.

7. The Sense of Hearing in the Goldfish, Carassius auratus L. Amer. Nat. Vol. 38, 275-284. 1904.

Bochenek.

Boeke.

8. Nowe szcze góly do budowy przysadki mózgowej plazów. (Neue Beiträge zum Bau der Hypophysis cerebri bei Amphibien). Bull. Internat. Akad. Kraków, 1902, 397-403.

9. Die Bedeutung des Infundibulums in der Entwickelung der Knochenfische. Anat. Anz., Bd. 20, 17-20.

Boveri.

10.

Brauer.

11.

1901.

Ueber die phylogenetische Bedeutung der Sehorgan des Amphioxus.
Zool. Jahrb., Suppl. 7 (Festsch. Weismann), 409-428. 1904.

Beiträge zur Kenntniss der Entwickelung und Anatomie der Gymnophionen. Zool. Jahrb., Suppl. 7, 381-408. 1904.

Braus.

12. Beiträge zur Entwickelung der Musculatur und des peripherischen Nervensystems der Selachier. Morph. Jahrb., Bd. 27, 415-496 ; 501-629.

Burckhardt.

1899.

13. Die Einheit Sinnesorgansystems bei den Wirbeltheren. Ber. ü. d. Verh. d. 5. Internat. Zool.-Cong. Berlin, 1901. 621-628.

Cameron.

14. On the origin of the Pineal Body as an Amesial Structure, deduced from the Study of its Development in Amphibia. Anat. Anz., Bd. 23, 394-395. 1903. Same title. Proc. Roy. Soc. Edinb., Secs. 190203. Vol. 24, 572-581. 1904.

15. On the Presence and Significance of the Superior Commissure throughout the Vertebrata. Jour. Anat. and Physiol., Vol. 38, 20-21. 1904.

Catois.

16.

Chiarugi. 17.

Coggi.

Recherches sur l'histologie et l'anatomie microscopique de l'encephale chez les poissons. Pp. 172. Lille. 1901.

Di un organo epitheliale situato al dinanzi della ipofisi e di altri punti relativi allo sviluppo della regione ipofisaria in embrioni di Torpedo ocellata. Monit. Zool. Ital., Vol. 9, 37-56. 1898.

18. Sulla sviluppo della Ampolle di Lorenz. Atti d. Reale Accad. dei Lincei. 1891, Ser. 4, Vol. 7.

19. Nouvelles recherches sur le developpment des Ampoules de Lorenzini. Arch. Ital. de Biol., T. 38, 321-333- 1902.

20.

Nuove richerche sulla sviluppo della ampolle di Lorenzini. Nota 1. Atti Accad. Lincei, Rendic. Cl. Sc. fis., mat., Anno 299, Ser. 5, Vol. 11, Fasc. 7, Sem. 1, 289-297. Nota 2, ibid., Fasc. 8, 338-340. 1902. 21. Sviluppo degli organi di senso laterale, della ampolle di Lorenzini e loro nervi rispettivi in Torpedo. Archivio Zool., Vol. 1, 59-107.

Coghill.

1902.

22. The Cranial Nerves of Amblystoma tigrinum. Jour. Comp. Neur., Vol. 12, 205-289. 1902.

Cushing.

23. The Taste Buds and their Independence of the N. Trigeminus. Deductions from Thirteen Cases of Gasserian Ganglion Extirpation. Johns Hopkins Hosp. Bull., Vol. 14, March-April, 1903.

Dogiel.

24. Das periphere Nervensystem des Amphioxus (Branchiostoma lanceolatum). Anat. Hefte, Bd. 21, 147-213. 1902.

Dohrn.

25. Die Entstehung der Hypophysis bei Petromyzon planeri. Mitth. Zool. Sta. Neapel, Bd. 4, 172-189. 1883.

26. Bemerkungen über den neuesten Versuch einer Lösung des Wirbel. thierkopf-Problems. Anat. Anz., Bd. 5, 53-64. 1890.