6 K. MIT.SUKUKI. 



}) V ( ) duce d solely 1j y t li e g r u w t li h a e k \v a r d o f t h e an t e r i o r 

 fold in conj unction with the lateral folds which ri«e grad- 

 uall\ from before backward. 



In the «taiie with two or three ]ne>s(jbla.stic somites, a> shoxNU 

 in Figs. 1> and 1^«, IM. 1. (see also Diag. II. and 11'. Tl. X.), the am- 

 niotic fold has extended nearly lialf o\er the body of the embryo 

 Avhose anterior pari has sunk meanwliüe more and more below ilie 

 level of the blastoderm. The jjosterior ii'dge of the amniotic hood 

 presents a horse-shoe shajjed outline, being caused by the lateral f )ld 

 of each side extending more posteriorly Ihan the median p;irl. fhere 

 are ;igain some irregidar folds (a) in the posterior parts (jt I he 

 embryonic region. 



Figs. o0-o3 (1*1. \'.) show a series of transverse sections selected 

 from différent parts of this embryo, Fig. oO being the most j>ostei'ior 

 and Fi"". o3 the most anterior. 



F^iiJ". 30 is from the region co\ered only bv the lateral lind),s of 

 the horse-shoe shaped posterior margin ol the amniotic hoixl. F'rom 

 this and Fig. oO« (PI. V.") (the latter representing the left half of 

 Fig. oO under a much higher powei" of magnilication) it will be seen 

 tliat the lateral f »Id of tlie amnion, when first laid, presents two 

 peculiarities: (1) it is purely epiblastic, ;uid the mesoblast has no 

 shave whatever in it ; (2) the fold is solid and not composed of I he 

 inner and outer limbs as re])resented in ordinary diagrams. 



F^ig. ol is just in front of the point where the two lateral am- 

 ni<jtic folds have united. One half of it i> shown under a hierher 

 power in Fig. öl</ (PI. \ .) j'he whole amnion here is composed of 

 a solid sheet of the e[)il)l:i.s|, I he mc>oi)I;ist insinuating it sell' between the 

 epiblast cells only later on. The cells of this part of the amnioji are in 

 se\ eral layers, and of these, the cells of the outermost layer have under- 

 gone some process of hardening and their nuclei are stained dee] 'est. 



