AISTD EMBRYOLOGY OF LIMULUS. 



11 



regarded the appendages of the Asaphus described by him in 1864. Since then the 

 researches of Mr. C. D. Walcott^ on sections of Trilobites seems to have satisfactorily 

 proved that Trilobites have rounded, jointed ambulatory appendages developed from the 

 head and possibly from the thorax. His observations, though from the nature of the case 

 in some respects imperfect, have set at rest the question as to whether these extinct 

 Palaeocarida had rounded, jointed limbs, though much yet remains unproved as to the 

 homologies of these limbs with those of the Merostomata. It also appears that the 

 hard parts of the eyes of Trilobites are directly homologous with those of Limulus, 

 as we attempt to show hereafter in this paper. 



o 







o 





5. 





'S 



^ 



a 

 o 



o 



Neocaeida. 



Pal^ocaeida. 



CRUSTACEA. 



As to the general homologies of the body of Limulus, it seems to us that the 

 facts presented further on confirm the position we have always taken, i. e., that there 

 are no true antennae in Limulus; that the gnathopods are mostly modified mouth- 

 parts, the last pair possibly representing a pair of thoracic feet; that the fore 

 region of the body corresponds to the cephalothorax of the Decapoda or of a 



1 Preliminary notice of the Discovery of Natatory and on some sections of Trilobites from the Trenton Limestone, 



Branchial appendages of Trilobites, and additional evidence Sept. 20, 1877. See also Ann. Rep. N. Y. Mas. Nat. Hist, 



upon the same. Twenty-eighth Annual Report, New York March, 1879. 

 State Museum of Natural History, December, 1876. Notes 



