32 AUTiini; nKNi>Y. 



the iiH'soMiisI (Iocs not iipiifiU' to cxtciul so far lis this, but 

 coast's sonu'wiiat aluuptly hcncath the rort'-lnaiii. It iTi'tainly 

 seems to roncspoiul to the spaces wliieli 1 have iileiitilied as 

 perioHVilial in earlier stajjes. In iVoiil ot the perleartlium the 

 eplhlast aiul hypohhist unite t(»j;t'ther eh)si'ly to tonn tlie vt'ry 

 thill pro-aniiiioii ot" the head region (ti<;. 50, Pro. Am.). 



'I'hf medulhivy eanal is now tloscd in iK>rsally, except in the 

 vej^ion oi (he tore-hrain, ami for a considerable space at tlu; 

 hinder imuI, above and in tVout of the luuirenteric eanal, ndiere 

 it still itpiMis wiilely into tlie amniotic cavity. ()\vin«; to the 

 peculinr buekward tilting ot" the head, the mill- ami hind brains 

 an> bent in a vertical plane somewhat into tin' I'orin t)t" the 

 lctt»r S, as sho\vn in tig'. 50. The I'ore-brain is slightly twisted 

 {o one side, so (hat its long axis lies oli'utpuly to the long axis 

 ot" the spinal ci>rd, ami the right and lelt halves ot" the roof ol' 

 the fore-brain overlap one another slightly in the middle line 



(tig. -IS). 



Stage II (tigs. 51 and 5.0). 



To this stage I reft>r embryo 7S, rei\ioved on neeembci Ittih 

 from an egg fiumd mi Stephens Islaml about the end o'i 

 November. Unfortumitely the himler half of this embryo was 

 accidentally injured after the first drawing (tig, M) had been 

 niade, so that 1 am \inable to give as full a description of it as 

 1 couhl wish. 



When viewed as an opaque objei't (he enibryo was seen to 

 ditl'er troni (he preceding stage chietly in the much greater 

 I'xteut to which tlu' ch)sure o( the >iliiiu-ntary eanal has ex- 

 tended backwards. Thus the vtMitral transverse fold (tig. 51, 

 l'\ Sp.) caused by (he (urning torwaril oi the spl.inchno[)leure 

 lies onlv a short way in tVont oi the middle oi the boily. The 

 enclosed portion of the alimentaiy canal (tig. 5.'J, Al. C.) is 

 tilled with yolk iKirtieles, whereby it is reiulertnl very con- 

 spicuous wlu'u the embryo is examined as a transparent object 

 after staining. Keneath the hiiuler part of this enclosed 

 portion lies the pericardium (tig. b'2, P. C) in (he form of a 

 sonu'what tpnulrangular sac, narrower in front than behiml. 

 In tlic pericarilium lies the heart (tig. 5:,*, lit.), in the t'orni oi 



