322 J. S. BUDGETT. 



yolk-plug, the abundance of yolk, and the mesoderm extending 

 only as far as the equatorial region of the egg. 



Section II passes longitudinally through the blastopore (6/.), 

 the walls of the neural groove being closed anteriorly, but not 

 yet posteriorly. The points to be noted are the anterior posi- 

 tion of the blastopore, the fusion of the embryonic layers before 

 and behind the blastopore, and anteriorly the beginning of the 

 first branchial pouch {br.f.). 



Section III, a sagittal section of an embryo after the closure 

 of the neural groove, showing the comparatively anterior posi- 

 tion of the neurenteric canal {n. en.), the brain vesicles, the 

 notochord not yet differentiated posteriorly, the archenteron, 

 and anteriorly the branchial fold [br.f.) of the pharyngeal 

 wall, which is continuous across the middle line ; also 

 posteriorly the depression which will later become the anus 

 {an.). 



Section IV is of the same series as the last, but further from 

 the middle line, showing the large lateral cavity of the arch- 

 enteron caused by the upraising of the branchial pouch {br.f.). 

 The section also passes through the optic vesicle {op. ves.). 



Section V is a transverse vertical section passing through 

 the head region of an embryo in which the body of the embryo 

 is just beginning to rise up off the yolk. To be noted are the 

 regularly formed optic vesicles {op. ves.) and stalks, there being 

 as yet no trace of the lens. Below is seen the pharyngeal 

 region of the archenteron (ph.). 



Section VI is of the same series as the last, passing between 

 the optic and auditory region ; it shows the single branchial 

 pouch {br.f.) and the accompanying epidermal thickening. 



Section VII of the same series, passing through the auditory 

 region. There are seen in section the front end of the noto- 

 chord {N. ch.), the auditory thickening of the epidermis {Aud.) 

 and the rudiment of the pronephros being differentiated off from 

 the general mesoderm {Pn.). There is seen also a faint indi- 

 cation of a neural crest {N. cr.). 



Section VlII of the same series, passing through the pos- 

 terior end of the archenteron, where it is seen to be constricted 



