EMBRYOLOGY OF LIMULUS POLYPHEMUS. 213 



before hatching ; whilst some, set aside at the' end of the season in a jar of salt water, 

 hatched out after some three hundred and fifty days from the time of spawning. 



He very justly estimates the rate of hatching to be due to the greater or less 

 exposure to light and warmth and to the oxygenation effected by the constantly 

 shifting tide-wave and the occasional exposure in damp sand or mud to the sun's rays at 

 low water. 



This exceeding vitality and fecundity may best explain the persistence of this genus 

 in time, a persistence probably unsurpassed by any among the Crustacean class save the 

 Entomostraca alone. 



Embryology of Limulus Polyphemus. 



So long ago as 1838 Professor H. Milne-Edwards 1 had examined the eggs of 

 Limulus containing the young ones about to be hatched ; he found that at this stage of 

 their development they present very little difference in the conformation of the anterior 

 portion of their body from that which exists in the adult ; but the abdominal portion of 

 the body bears only three pairs of appendages, and the long styliform tail-spine, so 

 remarkable in the adult, does not exist at all ; the form of the abdominal portion likewise 

 is equally different at this epoch. 



No further observations on the development of Limulus were made until the years 

 1869 and 1870, when the Rev. Samuel Lockwood, residing at Rariton Bay, New Jersey, 

 U.S.A., communicated the results of a series of observations made on the "Horse-foot- 

 crab " on that coast to the New York Lyceum of Natural History in October, 1869. 2 



Two valuable memoirs on the development of Limulus polyphemus have appeared (1) 

 by Dr. Anton Dohrn, 3 1871, (2) by Dr. A. S. Packard, jr. 4 (Preliminary paper 1870 and 

 full memoir, 1872.) 



We propose to quote chiefly from Dr. Packard's memoir as being the most recent 

 and also because he enjoyed greater facilities, both on account of frequent visits paid to 

 the coast, and also by constant inter-communication with Dr. Lockwood residing at 

 Rariton Bay, New Jersey, one of the regular resorts of the " Horse-foot-crab," as Limulus 

 is there called. During the progress of Dr. Packard's investigations, which extended over 



1 " Sur le Developpement des Limules ; Societe Philomatique," extr. ' Proc. verb.,' pp. 125, 126; 

 'l'Institut,' vi, No. 258, 1838, p. 397. 



2 Since published with additional matter in the 'American Naturalist,' vol. iv, July, 18/0, pp. 257 — 

 274. 



3 " Zur Embryologie und Morphologie des Limulus polyphemus ;" von Dr. Anton Dohrn (' Jenaische 

 Zeitschrift,' Band vi, Heft 4, p. 580, Tafeln xiv and xv), received September 30th, 1871. 



4 "On the Embryology of Limulus polyphemus,'''' by A. S. Packard, jun., M.D. Read before the 

 American Association for the Advancement of Science, August, 1870 ('American Naturalist,' vol. iv, 

 No. 8, October, 1870, p. 498). 



"The Development of Limulus polyphemus,'''' by A. S. Packard, jun., M.D., read November 16th, 

 1870, 'Mem. Bost. Soc. Nat. Hist.,' vol. ii, 1872, pp. 155—202, 3 plates, 4to. 



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