PLATE VII. 

 LATBR EMBRYOS. 



(Preparations magnified about 25 diameters.) 



a. Anus. ot. Otic vesicle. 



at. Atrium. ot. o. External opening of otic vesicle. 



b. Epiphysis. p. Pineal outgrowth. 



c. Conus arteriosus. -p. a. g. Postanal gut. 

 c. e. Caudal eminence. n. Pronephros. 



c. v. Caudal vein. fn, d. Pronephric duct. 



g j , g". Gill slits. f. f. Pectoral fin. 



k. Cephalic knob. s. Spiracle. 



of. Optic vesicle. s. v. Sinus venosus. 



v. Ventricle. 



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, k. in the region of the forebrain. 



Fig. 42 a and b. 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 b. 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.) 



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