ON THE PATE OP THE BLASTOPOEE IN THE NEWT. 177 



Mr. Sedgwick for his kindness in helping me both in my work 

 and in the preparation of this paper. 



EXPLANATION OF PLATE XVII. 



Illustrating Miss Johnson's paper on " The Fate of the Blas- 

 topore and the Presence of a Primitive Streak in the 

 Newt." 



List of References. 



a. Archenteron. au. Auditory vesicle, b. c. Body-cavity, bl. Blastopore. 

 ch. Notochord. ch! Rudiment of notochord. ep. Epiblast. ep' . Thickened 

 epiblast of medullary area. fb. Fore-brain, fg. Fore-gut. h.g. Hind-gut. 

 hy. hypoblast, m. c. Medullary canal, m. c! Solid medullary canal, mes. 

 Mesoblast. m.s. Mesoblastic somite, o.v. Optic vesicle, pr.g. Primitive 

 groove, pr. s. Primitive streak, s. Space between hypoblast and mesoblast, 

 v.c. Outgrowth of fore-gut to form visceral cleft. 



Fig. 1. — Transverse section through embryo before the formation of the 

 medullary folds. The section is taken through about the middle of the 

 embryo. 



Fig. 2. — Transverse section through the same embryo, taken at some dis- 

 tance further forwards. 



Figs. 3, 4, 5. — Transverse sections through embryo in which the formation 

 of the medullary folds has just taken place, and the medullary area is still 

 very broad. Fig. 3 passes through the blastopore, and is the most posterior 

 of the series. Fig. 4 is taken through the dorsal surface at some distance in 

 front of the blastopore. Fig. 5 is the most anterior of the series near the 

 front end of the posterior part of the primitive groove. 



Figs. 6, 7, 8, 9. — Transverse sections through an embryo with several meso- 

 blast somites. Fig. 6 is the most posterior, and fig. 9 the most anterior of 

 the series. 



Fig. 10. — Section through the primitive streak of an older embryo, with 

 rudiments of the visceral clefts, tail, &c. The section is oblique, i. e. between 

 the transverse and horizontal planes, consequently the primitive streak appears 

 deeper than usual. 



Fig. 11. — Longitudinal section through the hind part of an embryo with 

 the medullary folds just closed. The section is slightly oblique. 



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