574 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



PLATK LVI. 



(Stage XII.) 



FIGS. 224-235. Serial transverse sections through the first larvar, continued from Plate LV. x73. 



REFERENCE LETTERS. 



Ab. I', fifth abdominal app 



o. i. a., inferior abdominal aorta. 



a. op., ophthalmic artery. 



<i..a., superior abdominal artery. 



hi/., branchiostegite. 



In-., branchia of ambulatory appendage. 



It. .s'., blood sinus. 



gg. '~ 3 , middle, ventral, and dorsal lobules of posterior lobe of midgnt. 



H., heart. 



hi/., hindj;nt. 



hi/., hypodermis. 



Ic. Hi. -nli., longitudinal commissures uniting last thoracio wilh lirst abdominal 



My., midj;iit. 



Mg. '', lati'ral lobe of undent. 



Mil. ', posterior lobe of midgut. 



.U., masticatory stomach. 



.!/.<., extensor muscles of abdomen. 



Mii.f.. tlexor muscles of abdomen. 



.V.rjirZ. I-Ifl, tirst to third maxillipeds. 



/ili ii.. plenron. 



ps., pericardia! H\I\MS. 



Th. I-V, first to fifth ambulatory limb. 



