562 MEMoiKs or the national academy of sciences. 



1'late L. 

 (St:igo XL) 



Figs. 177-179, LSI, 182. Serial tiau.svi'rse vsectiiius of the eiiibijo of AJphaoi hefetoclwlis, which is 

 ueaily reaily to hatch. The shell is soiuewhat diagraiiiaticailj lepresenteil audappeais 

 thickened in Fig. I<S2, owing to a coagulable substance beneath It. The cells rep- 

 resented in the .yoiU in Fig. 182 appear to be endodenii cells, which have become 

 mechanically detached from the walls of the meseuteron. x74. 



Fig. 180. Nearly median longitiidiual section through a similar embryo. The eudodermal lining 

 of the meiseuteron i.s not yet nearly completed, x 74. 



REFERENCE LETTERiS. 



Ab., VI, gauglioii ofnixtU :il)<luiiiiii:il appi'uilago. 



ag., nulenual gaugli»ii. 



ans., anus. 



ch.ex., external uhiasiiia. 



cct., ectoderu). 



end., endoderuj. 



/</., foregut. 



ijma., anterior gastric muscle. 



//., heart. 



7i(/., biudgut. 



hi/., Uyjiodcrniis. 



If., lateral fiber-niaiss of biaiii. 



OTjt. , meseuteron. 



mg.' ?/u/.^ of other lignres, pustcriii: lobe of midgut. 



»««./., liexor muscles of midgut . 



mil. «., extensor muscles of midgut. 



vein., (esophageal couiuiissure. 



o.pri., optic iieihincle. 



I{et., retiiiii. 



nog., brain. 



T., telson. 



1-4, ganglia of e.ve-stalk. 



