DESCRIPTION OF PLATES VI, VII, VIII & IX, 



Illustrating Mr. Walter Heape's Memoir on the " Develop- 

 ment of the Mole (Talpa Europea). The Formation 

 of the Germinal Layers, and Early Development of the 

 Medullary Groove and Notochord." 



List of Reference Letters, 



a. a. Cut edges of uterus, am. Amnion, hi. cav. Cavity of blastodermic 

 vesicle. II. of B. Blastopore of van Beneden. hip. Blastopore, c. m. Cir- 

 cular muscles, c. t. Connective tissue, ep. Epiblast. ep. k. Epiblast keel. 

 hy. Hypoblast, hy. m. Hypoblastic mesoblast. i. m. Inner mass. /. m. 

 Longitudinal muscles, m. Mesoblast. m. c. Mucous envelope, mes. Meso- 

 blast. m. gr. Medullary groove, m. pi. Medullary plate, n. c. Neurenteric 

 canal, nch. Notochord. nch. c. Notochordal canal, o. l. Outer layer. 

 p. gr. Primitive groove, pi. Papilla, p. sk. Primitive streak, p. sk. An- 

 terior end of primitive streak, sec. c. Secondary cavity between inner mass 

 and outer layer, sp. Artificial space between zona and outer layer, spt. Septa 

 of connective tissue, t. c. Transition cells, tr. Rudimentary trager. ut. ep. 

 Uterine epithelium, ut. gls. Uterine glands, ut. gls'. Mouths of uterine 

 glands, z. Zona. 



Mr. H. A. Chapman, of the Fitzwilliam Museum, Cambridge, has drawn for 

 me figure 51 and all the figures on Plate VI, with the exception of figure 4. 



PLATE VI. 



Fig. 1. — An optical section of a fully-segmented ovum showing the outer 

 layer (o. I.) and the inner mass {i. m.) of segments, the blastopore of van 

 Beneden {hi. of B.) perforating the outer layer, the radially striated zona {z), 

 and the outer gelatinous mucous covering {m. c.). The whole ovum inside the 

 membranes is "15 mm. by '17 mm. in diameter, diameter of inner mass is •! by 

 •12 mm., of outer layer "05 mm. ; zona measures '01 mm., and mucous envelope 

 •014 mm. in thickness. ( X 177 times.) 



Fig. 2. — An optical section of an ovum soon after the appearance of the 

 blastodermic cavity (Jbl. cav.). Beneden's blastopore is closed. The whole 

 ovum inside the zona is ^12 mm., and the inner mass '06 mm, in diameter. 

 ( X 177 times.) 



Figures 1 and 2 are silver nitrate preparations. 



