Xliv EXPLANATION OF PLATE 33. 



Fig. 1 6. Transverse section through the ventral plate in the thoracic region 

 of an embryo of the same age as fig. 7. 



Fig. 17. Transverse section through the procephalic lobes of an embryo of the 

 same age. gr. Section of hemicircular groove in procephalic lobe. 



Fig. 1 8. Transverse section through the thoracic region of an embryo of the 

 same age as fig. 8. 



Fig. 19. Section through the procephalic lobes of an embryo of the same age. 



Fig. 20 a, b, c, d, e. Five sections through an embryo of the same age as fig. 9. 

 a and b are sections through the procephalic lobes, c through the front part of the 

 thorax, d cuts transversely the posterior parts of the thorax, and longitudinally 

 and horizontally the ventral surface of the abdomen, e cuts the posterior part of the 

 abdomen longitudinally and horizontally, and shews the commencement of the 

 mesenteron. 



Fig. 21. Longitudinal and vertical section of an embryo of the same age. The 

 section passes somewhat to one side of the middle line, and shews the structure of the 

 nervous system. 



Fig. 22. Transverse section through the dorsal part of the abdomen of an embryo 

 of the same stage as fig. 9. 



EXPLANATION OF PLATE 33. (XX. p. 714.) 



Fig. i. Transverse section through the pelvic fin of an embryo of Scyllium 

 belonging to stage P 1 , magnified 50 diameters. bp. basipterygium. br. fin ray. 

 ;;/. muscle, /if. horny fibres supporting the peripheral part of the fin. 



Fig. 2. Pelvic fin of a very young female embryo of Scyllium stellar e, magnified 

 1 6 diameters, bp. basipterygium. pu. pubic process of pelvic girdle (cut across 

 below), il. iliac process of pelvic girdle, fo. foramen. 



Fig. 3. Pelvic fin of a young male embryo of Scyllium stellare, magnified 16 

 diameters, bp. basipterygium. mo. process of basipterygium continued into clasper. 

 il. iliac process of pelvic girdle, pu. pubic section of pelvic girdle. 



Fig. 4. Transverse section through the ventral part of the trunk of an embryo 

 Scyllium of stage P, in the region of the pectoral fins, to shew how the fins are 

 attached to the body, magnified 18 diameters, br. cartilaginous fin-ray, bp. basi- 

 pterygium. m. muscle of fin. mp. muscle-plate. 



Fi g- 5' Transverse section through the ventral part of the trunk of an embryo 

 .Scyllium of stage P, in the region of the pelvic fin, on the same scale ap fig. 4. 

 bp. basipterygium. br. cartilaginous fin-rays. ;. muscle of the fins. ;///. muscle- 

 plate. 



5. Pectoral fin of an embryo of Scyllium canicula, of a stage between O and 

 P, in longitudinal and horizontal section (the skeleton of the fin was still in the condi- 

 tion of embryonic cartilage), magnified 36 diameters, bp. basipterygium (eventual 



' I employ here the same letters to indicate the stages as in my "Monograph on Elasmobranch 



