542 STRUCTURE OF THE LARVAL POLTPTERUS. 



PLATE XXXIV. 



Fig. ] . A section tlirougli the alisj)lieiioid region of the head cutting the median vesicle, epiphysis, 

 and cartihiginous bridge in the region of the epiphysis, also cutting the trabeculse cranii, 

 the sphenotic wings, and palato-quadrate bars, x 30. 



Fig. 2. A section through the vertebral region of the axial skeleton in the anterior part of the body 

 of the 30 mm. larva. Showing the neural, lateral, and ventral processes abutting on the 

 notochord, also tlie outer portion of the cartilages of the lateral ribs, x 30. 



Fig. 3. A section through the same region in a 9 cm. specimen, showing the encrusting tony 

 dcjjosits forming the vertebra: with their large transverse process. The ventral processes 

 no longer abut on the notochord. X 22. 



Fig. 4. A similar section in the hind part of the body of a 9 cm. specimen, showing the carti- 

 laginous ventral processes now forming the heads of the ventral ribs attached to the 

 undersides of the extremities of the bony transverse processes. The ventro-lateral muscles 

 likewise have retreated i'rom contact with the notochord. X 22. 



Fig. 5. A section through the vertebral region of the axial skeleton in the anterior part of the 

 body of a 13 em. specimen, showing the increased development of the bony vertebrae, the 

 complete suppression of the cartilages of the axial skeleton, and the vertebrally constricted 

 notochord. x 15. 



Fig. 6. A section through the intervertebral region of the same series as fig. 5, showing the inter- 

 vertebral dilatation of the notochord, especially of its sheath, which is enclosed in a single 

 layer of cartilage-like cells, x 15. 



Fig. 7 . A slightly oblique longitudinal section through the ventro-lateral muscles in a 9 cm. 

 specimen, showing the head of the ventral rib to the left containing the cartilage of the 

 ventral process and lying in front of the transverse process, and the continuation of 

 the ventral ribs outwards and backwards towards the right. The figure has been put 

 on the Plate in two portions. x 20. 



Fig. 8. A section of the same series as fig. 7, but in the middle of the vertebral centra on the left, 

 sloping outwards through the sides of the vertebrte towards the right. Two cartilaginous 

 neural processes are seen towards the middle of the figure embedded in the bony centra, 

 further to the right the section passes thi'ough the bony neural arch, while on the right 

 of the figure are seen two lateral cartilaginous processes. x 20. 



Fig. 9. Is a reconstruction of the pronephros of the right side of the 30 mm. larva, and viewed 

 from the head ward side, with the glomus lying under the notochord and the coiled 

 portion of the pronephric duct lying between the brachial nerve and the skin. The 

 notochord, dorso-lateral muscles, and ventro-lateral muscles are seen only in section, x 70. 



Fig. 10. Is a similar reconstruction of the most anterior mesonephrie tubules of the right side, 

 showing that they do not lie in the same region of the body as the coiled duct of the 

 pronephros, but much nearer the middle line close under the notochord, and that they 

 end anteriorly quite suddenly. X 70. 



