THE CEPHALIC NAVEL. 



241 



'.cm. ptl-,(>. 



143 



. G 



14-i 



H 



■^fi^f 



PM^ 



4H^^ 



Fig. 143. — Limulus embryo, stage G. Note the segmental sense organs, and the absense of segmented thoracic 



plates. 

 ' Fig. 144. — Same, stage H. The haemal portion of the blastoderm, just beyond the germ wall, is beginning to pro- 

 liferate, marking the beginning of the dorsal organ, or cephalic navel, d.o. 

 Fig. 145. — Same, stage I. The entire hsemal blastoderm is in active proliferation. 

 Fig. 146. — Same, stage J. The germ wall and vascular area are very conspicuous; the posterior limb of the 

 germ wall has moved forward to the haemal portion of the thorax, narrowing the area of the cephalic navel. 



Fig. 147. — Same, stage K. The abdominal lobe is distinctly marked off; the lateral eye. I.e., has moved back- 

 ward into the fourth thoracic segment, and the cephalic navel is confined to the hcemal surface of the anterior 

 thoracic region. 



Fig. 148. — Same, stage L. The full complement of branchial segments have appeared, and the margins of 

 th'ir lateral plates have united on the haemal surface to form the heart; the lateral eye lies hsmal to the tho- 

 racic sense organ. 

 16 



