Plate VII. 

 Later Embryos. 



(Preparations magnified about 25 diameters.) 



Fig. 42. — Embryo, age about 25 days, corresponding to Balfour's stage g (+) of shark. This 

 embryo bent during the process of fixation. It shows especially well the knob-like out- 

 growth, /'. in the region of the forebrain. 



Fig. 42 a and /'.^Anterior region of preceding embryo. Shown in nearly lateral and in dorsal 

 aspect. 



Fig. 43. — Embryo, age about 29 days, corresponding approximately to Balfour's stage I in shark. 



Fig. 43 h. — Anterior region of specimen similar to preceding. 



Fig. 44. — Embryo, age about 31 days, corresponding approximately to Balfour's stage j in shark. 

 It shows a bulbous caudal thickening. 



Fig. 45. — Embryo, age about 40 days, corresponding approximately to Balfour's stage k in shark. 

 The circular area under the letters g:' g." was found to be artifact. 



Fig. 46. — Embryo, age about 45 days, somewhat more advanced than Balfour's stage L in shark. 

 At the time of fixation the embryo probably twisted, so that its axis came to lie nearly 

 parallel to the neighboring margin of the blastoderm. (Length of embryo 20 mm.) 



186 



