310 



THE DEVELOPMENT OF THE VENTRAL NERVES IN SELACHII. 



Sedgwick, A. 



'94. On the Inadequacy of the Cellular Theory of Development, and on the Early Development of Nerves, 

 particularly of the Third Nerve and of the Sympathetic in Elasmobranchii. Quart. Jour. Micr. 

 Sci., vol. 37, no. 145, pp. 87-101. 

 Van Wijhe, J. W. 



'89. Ueber die Mesodermsegmente des Rumpfes und die Entwickelung des Excretionssystems bei Sela- 

 chiern. Arch. mikr. Anat., Bd. 33, pp. 461-516, Taf. 30-32. 



Vignal, W. 



'88. Recherches sur le deVeloppement des elements des couches corticales du cerveau et du cervelet chez 

 1'homme et les mammiferes. Arch, physiol. norm, et path., s<jr. 4, torn. 2, pp. 228-254, 311-338, 

 pis. 5, 6, 9-12. 

 Wlassak, R. 



'98. Die Herkunft des Myelins. Ein Beitrag zur Physiologic des nervosen Stiitzgewebes. Arch. f. Ent- 

 wick-mech., Bd. 6, Heft 4, pp. 453-493, Taf. 26-29. 



EXPLANATION OF PLATES XXII-XXIV. 



ABBREVIATIONS. 



ao. d. 

 cd.d. 

 cl. crs. n. 

 cl. n'U. 

 e'n. 



gn. spi. 

 la. ct. 

 la. mu. 

 mb. cl. 

 mb. Urn. 

 ms'ec'drm. 

 ms'ench. 

 ms'en'drm. 



Dorsal aorta. 

 Chorda dorsalis. 

 Neural crest cells. 

 Neuroblast cells. 

 Epineurium. 

 Spinal ganglion. 

 Lamina cutis. 

 Lamina muscularis. 

 Cell membrane. 

 Limiting membrane. 

 Mesectoderm. 

 Mesenchyme. 

 Mesentoderm. 



my'tm. 



riax. 



rid. 



nidi. 



nl. 



pi'n. 



rx. v. 



sb'sta. i'fbrl. 



so. 



tb.n. 



tu. med. 



tu. Schw. 



vac. 



Myotome. 



Neuraxon. 



Nodus. 



Nidulus. 



Nucleus. 



Perineurium. 



Ventral root. 



Interfibrillar substance. 



Somite. 



Neural tube. 



Medullary sheath. 



Schwann's sheath. 



Vacuole. 



All the figures were drawn with the Abb6 camera. Except Figures 29-32, Plate XXIV, all were drawn from 

 sections of embryos of Squalus acanthias. All the specimens from which the drawings were made were fixed in 

 vom Rath's picro-osmo-aceto platinic chloride mixture and treated subsequently with either pyroligneous or 

 pyrogallic acid. 



PLATE XXII. 



All the figures are camera drawings of cross-sections except Figures 10 and 11, which are frontal sections. With 

 these exceptions all are viewed posteriorly, so that right in the figure corresponds with right in the embryo. The 

 sections are all taken in the posterior half of the bod}-, Figures 1-3 from an 8-mm. embryo and Figures 4-10 from 

 a 10-mm. embryo. The portions of the cross-sections represented in the figures are indicated by a circle in 

 Figure 5. In some cases the developing nerve of the left side and in others that of the right side is represented . 

 Taken as a whole the figures of Plate XXII represent a series of stages in the development of a spinal ventral nerve 

 from the time of its first appearance as a process of a single neuroblast cell until the developing nerve contains its 

 chief constituents, neuraxones and neurilemma cells. The series also presents evidence of the migration of 

 cells from the neural tube. 



