l6o ELEMENTARY BIOLOGY. [CHAP. 



i 



II 



the whole having undergone a slight increase i 

 total capacity and lost its spherical shape. 



a. The blastopore; still visible but small and 

 excentric (displaced towards the flattened or 

 dorsal surface). 



ft. The neural plate ; obvious as a lyre-shaped flat 

 tening, in front of and in a line with the blasto- 

 pore ; its edges thickened and raised up (^neural 

 folds), its mid region depressed {neural grooz>e). 



The neural folds will in all probability be seen 

 to unite in front, and die away behind, at the sides 

 of the blastopore. A more or less marked ap- 

 proximation of their hinder halves will be obvious. 



The safne at 12 — 14 days. 



The embryo may now be definitely recognized as 

 a pear-shaped body still enclosed within the mu 

 cous investment. Remove and examine it. 

 a. The body ; head and trunk, very obvious if see 

 from the dorsal aspect. 



/?. The neural folds ; seen, if examined from the 



dorsal aspect, to be uniting in the middle line. ,,. 

 y. The blastopore ; no longer recognizable. fl| 



Z. The suckers; two oval thick-lipped depressions 



on the under side of the head (mouth not yet 



recognizable). 

 €. The visceral arches ; generally to be seen at thii 



stage, as a couple of oblique ridges on either 



side, above 8. 



The embryo at 15 — 18 days. 



Still enclosed within the mucus mass ; recognizi 



ji 



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