558 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Platk XLVIII. 



(Stage X.) 



Figs. 162-165. Parts of serial sections through the region of the heart and thoracic-abdominal 



fold to show the extension and relations of the endoderm. x57. 

 Figs. 166—167. Parts of serial transverse sections of the embryo of Alpheus sanlcyi. x 125 

 Fig. 168. Median longitudinal section through a slightly older embryo, showing the ventral 

 endodermic fold (/). the foregnt still screened from the yolk, and the nervous 

 system separated from the skin. x227. 



REFERENCE LETTERS. 



Ah , abdomeii. 



Ab. g. I, first abdomiual ganglion. 



aor., aorta. 



B. v., blood cell. 



B. S., blood space. 



cc, cryBtalline cone cells. 



Deg., products of degeneration. 



Sep., proximal retinular cells. 



Knd., endoderm. 



/., ventral endodermic fold. 



g. m. a., anterior gastric muscle. 



M., heart. 



Hg., hindgut. 



imb., intercepting membrane. 



mg., mesenteron. 



mo., mouth. 



mpgl, first maxillipedal ganglion. 



Mii.JE., extensor muscles. 



Mu.f., flexor muscles. 



0. G., optic ganglia. 



l>. -1., pericardial sinus. *■ 



A'*., retinogen. 



i?. O. (;., suprarOBSophageal ganglion. 



T., telson. 



Til., thorax. 



Th.g. I, ganglion of first ambulatory limb. 



y. c, wandering cells. 



