58 PEOCEEDmGS OF THE GEOLOGICAL SOCIETY. [DeC. 20, 



To conclude, then. : — 



1. According to Dr. Packard there is a Nauplius-stage passed 

 by Limulus in the a^g. (He, however, does not seem quite to 

 understand what is meant by a Naupliiform larva.) He admits 

 that it is not like the " Wauplius " of Apus or of BrancJivpus, but is 

 to be compared rather to that of the Trilobites, a knowledge of 

 which we do not possess. 



2. If Limidiis is brought nearer to Trilobita through the discovery 

 of the specimen of Asaphus (recently exhibited here by Mr. E. Bil- 

 lings, r.G.S., the eminent palaeontologist to the Geological Survey of 

 Canada, and figured in Quart. Journ. Geol. Soc. 1870, vol. xxvi. 

 p. 479, pis. xxxi. & xxxii.), we have failed to understand its 

 nature. The specimen is believed to possess eight pairs of five- 

 jointed walking-feet attached to the movable (thoracico-abdominal) 

 segments of the body, not a series of mouth-feet (gnathopodites), as 

 in Limulus, but rather like the thoracic legs in the Isopoda. 



3. That which really does bring the Trilobites near to Limulus 

 is the series of embryonal changes passed through by the latter in 

 the egg, which resemble the young of the former, and which agree 

 also with the young state in the Isopoda *. ' 



4. With regard to Dr. Dohrn's investigations, much as he has 

 done, he admits that many more points remain in uncertainty — 

 for instance, the neurology of the embrjo, the development of the 

 lower Hp, &c. 



, 5. The Nauplius-stage, too, is left in doubt ; he is only able to 

 compare the subsequent stages with the young Trilobite and with 

 Belinurus and PrestwicMa. With these latter I had already com- 

 pared the larval Limulus figured and described by Milne-Edwards 

 in 1838 f. 



6. Not having dissected Limulus, I was unable either to rebut or 

 to confirm Van der Hoeven's and Dr. Dohrn's arguments as to the 

 presence of only one pair of anterior extremities supplied with 

 nerves from the supracesophageal ganglion ; but, through the kind- 

 ness of Professor Owen, who has lately been carrying on, or rather 

 renewing, some researches made long since, upon the neurology of 

 Limulus, I am able to state upon his authority that Limulus pos- 

 sesses two distinct pairs of appendages (antennules and antennae) 

 which derive their neuration from two pairs of nerves given off 

 from the supracesophageal ganglion. Yan der Hoeven's statement 

 must therefore be considered incorrect %. 



7. With regard to the Eurypterida, so far as our present know- 



* From Fritz Miiller's ' Facts and Arguments for Darwin ' (translated and 

 edited by Mr. W. S. Dallas, F.L.S., the Assistant Secretary to the Geological 

 Society), it seems evident that, upon embryological grounds, many Crustacean 

 orders and families might be united together. 



t See my paper, Quart. Journ. Geol. Soc. 1867, vol. xxiii. p. 34. 



I Professor Owen informs me that he has pointed out, in his paper on the 

 anatomy of Limuhcs (not yet published), that he observes, in the innervation of 

 the great ensiform caudal spine, evidences of several pairs of nerves divided into 

 dorsal and ventral branches, which he considers can only be explained on tlie 

 assumption that the spine is not a simple median appendage or terminal plate 



