The Development of Theridium. 351 



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glichen iiiit derjenigeu eiuiger auderer Aracliniden. Zeit. wiss. 

 Zool., SI. 



Simmons, O. L., 1S94. Developmeut of the Lungs of Spiders. Amer. Journ. 

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EXPLANATION OF PLATES I-VIII. 



All the drawings are made with the camera lucida, and in the greater 

 number the yolk has been represented by simple shading. The arrow on some 

 of the figures points to the anterior (cephalic) pole. The following abbrevia- 

 tions Iiave been employed : 



Ab. 1-Ab. 8, Abdominal segments 1-8. 



Ab. 2. B-Ab. 5, B., limb buds of abdominal segments 2-5. 



Ab. G. 1-Ab. G. 6, abdominal ganglia 1-6. 



A. L. v., antero-lateral vesicle. 



Bl, blood-cell. 



Gaud., caudal lobe (telson). 



Cav., central fluid cavity within yolk. 



Cav. B., outer boundary of this cavity. 



Ce. G., cerebral ganglion. 



Ceph., cephalic lobe. 



Ce. R., cerebral ridge. 



Chel., cheliceron. 



Chel. Coel., cheliceral coelom. 



Chel. G., cheliceral ganglion. 



Chel. Mes., cheliceral mesoblast. 



Coel., coelom. 



Cum. A., anterior cumulus. 



Cum. P., posterior cumulus. 



Cyt., cytoplasm. 



Ect., ectoblast. 



Ent., definite entoblast. 



Ex., extraembryonic blastoderm. 



Fov., fovea semicircularig. 



Gang., ganglion. 



Gast., gastrocoel. 



G. B., peripheral boundary of germ disc. 



G. C? germ cell. 



H., heart. 



L. 1-L. 4., ambulatory appendages (or their segments). 



