THE DEVELOPMENT OF THE MOLE. 139 



DESCRIPTION OF PLATES XIII, XIV, & XV, 



Illustrating Mr. Walter Heape's Paper on " The Development 

 of the Mole (Talpa Europea)," Stages E to J. 



List of Reference Letters. 



a. are. Aortic arch. a. c. v. Anterior cardinal vein. al. c. Alimentary 

 canal, all. Allantois. all. v. Allantoic vessels, am. Amnion, am.fi. False 

 amnion. ««./i. Anal pit. a.jo. Area pellucida. «z<(^. e/;. Auditory epithelium. 

 aud. inv. Auditory involution. b. c. Body cavity. c. pi. Cephalic plate. 

 d. a. Dorsal aorta. ep. Epiblast. f. br. Eore-brain. h. br. Hind-brain. 

 ht. Heart, hy. Hypoblast, i. c. a. Internal carotid artery, t. c. m. Inter- 

 mediate cell mass. m. Mesoblast. m. br. Mid-brain. m. gr. Medullary 

 groove, m. pi. Medullary plate, msc. pi. Muscle-plate, n. c. Neural canal. 

 nch. Notochord. op. gr. Optic grooves, op. v. Optic vesicles, p. c. Peri- 

 cardial cavity, pro. am. pro-amnion. p. st. Primitive streak, p. v. Proto- 

 vertebra. Si. rk. Sinus rhomboidalis. so. m. Somatic mesoblast. so. pi. 

 Somatopleure. sp. m. Splanchnic mesoblast. sp. pi. Splanchnopleure. v. a. 

 Vertebral artery, vs. ach. Visceral arch. vt. a. Vitelline artery, vt. v. Vi- 

 telline vessels, vt. vn. Vitelline vein. 



Figs. 1 — 10 were sketched with Zeiss's a* lens and eye-piece 2 by myself, 

 and were most carefully shaded by Mr. H. A. Chapman under my supervision. 



Figs. 11 — 35, 44 — 50, and 52 were sketched with Zeiss's b lens and eye- 

 piece 2. 



Figs. 36 — 43 and 51 were sketched with Zeiss's D leus and eye-piece 2. 



Fig. 1, Stage E. — Transparent view of embryo 76 mm. long. It has three 

 protovertebrae. The medullary groove is narrow in the middle of the body, 

 widening out at either end. The anterior end of the primitive streak projects 

 as a dark knob into the wide sinus rhomboidalis. The flattened cephalic plate 

 (c. pi.) and the area pellucida {a. p.) are to be observed. 



Fig. 2, Stage E. — Surface view of embryo 1"82 mm. long. The cephalic 

 plate has now two deep lateral grooves, the optic grooves {pp.gr.). The 

 curved condition of the embryo is due to careless manipulation. 



Fig. 3, Stage F. — Surface view of embryo 1'96 mm. long. The medullary 

 groove has commenced to close in the region of the protovertebrae (which are 

 not shown in this drawing), but the edges of the groove have not yet 

 coalesced. The optic grooves are seen at either side of the cephalic plate. 



Fig. 4, Stage F. — Surface view of embryo 2-12 mm. long. Although some- 



