PLATE LXXIII. 



Kli:. 168. Vertical section of peripheral part of blastoderm of trout's egg at the fourteenth day. 6. Margiua 

 thickening, c. Central thin portion of blastoderm, showing superficially a layer of flattened elements, undT 

 which is a layer of spheroidal elements, d. The blastoderm rests on the yolk by means of the sub-germinal 

 processes, as in fig. 167. The formative elements, e, on the floor of the cleavage cavity, a, are derived from 

 the blastoderm ; either from the sub-germinal processes, or from the lower layer, d, of the central portion. 

 f. Yolk of the saucer-shaped depression, g. Vacuoles (fat globules?). 



PIG. 173. Vertical section of the dorsal furrow of the commencing embryo of bufo einereus. ,/. Corne;. 

 layer. 6. Dorsal furrow, c. C''>mmeneii!>.: crninil i; t -r\ous system. *'. <'ommeneim: r1i<>r<l<t tl>>r*itfix. .-. IVn- 

 pheral portion of nervous layer. /. Peripheral portion of the third or motor-germinative layer. </. Fourth ..r 

 epithelial glandular layer, h. Knseoni's uavil.y. II. Klemvnts of Ki-ichtrl' uuntral yolk lAAM. k. The ra- 

 inainder of the cleavage cavity, p. 133, 



