562 MEMOlIia OF THE NATIONAL ACADEMY OF SCIENCES. 



IY.ATK L. 

 (Shu.;,. XI.) 



FlGS. 177-170, IS], 182. Serial transverse sections of the embryo of Alplint* JtctcrtH-Iirlis, which is 

 nearly ready to hatch. The shell is somewhat diagramatically represented and appears 

 thickened in Fig. 182, owing to a coagnlable substance beneath it. The cells rep- 

 resented in the yolk in Fig. i *- appear to be endodemi cells, which have become 

 mechanically detached from the walls of the mesenteron. x 74. 



FlG. 180. Nearly median longitudinal section through a similar embryo. The eiidodermal lining 

 of the mesenteron is not yet nearly completed. x74. 



DEFERENCE LKTTKRS. 



.tl>., VI, ^an^lion nl'sixlli ;iliiliiniiii:il :i)i|irinlage. 



(/., aiitcnnal uniinlion. 



aus., mins. 



ch.er., oxti'rual c-liiasnia. 



<<!., ectoderm. 



cnii.. eniloderiii. 



./(/., forejjnt. 



ijma., anterior Kast.vii: imiHi'lf. 



//., heart. 



/ii/., liindgnt. 



hy., hypndermis. 



If., lateral fiber-mass of luain. 



mil , mesenteron. 



tin/. 1 wiiy.^ of otber figflres, jiosii-iio: lobo of midgut. 



mii.f., Ili-xor muscles of inid^iil . 



.(., extensor muscles nf niid^ut. 



nciii.. irsophageal eDinmissnre. 



n. jiil.. <i)>tic iKNlnnrli-. 



llt-l., retina. 



MI;/., brain. 



T., telson. 



1-1, ganglia of eye-stalk. 



