THE CEPHALIC NAVEL. 



241 



M 



143 



G 



144 



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 '-'..'-.* v '"?- f .\. -.;>;.. XK I 



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L 



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 haemal 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 hasmal 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 hamal 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 haemal to the tho- 

 racic sense organ. 



16 



