PLATE VII. 



L,ATER EMBRYOS. 



(Preparations magnified about 25 diameters.) 



a. Anus. ot. Otic vesicle. 



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



ft. Epiphysis. 1>. Pineal outgrowth. 



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



c. e. Caudal eminence. pn. Pronephros. 



c. v. Caudal vein. fm. d. Pronephric duct. 



g 1 , g". Gill slits. $. f. Pectoral fin. 



k. Cephalic knob. s. Spiracle. 



op. 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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