OF THE AMERICAN KING-CRAB. 497 
The anatomical investigations of well-preserved mature King-crabs, the results of 
which are given in a previous section ($ 4) of the present memoir, have convinced me 
that Limulus, like other Crustacea, does derive the nerves of its two anterior pairs of 
cephaletral limbs (11, 111) from the cerebral (=supercesophageal, here preecesophageal) 
ganglion. The portion sending off the nerves of rr. and 111. is not, indeed, so distinct 
from the rest of the neural circle as in Astacus; but it holds the same relative position 
to the gullet. It is even within the bounds of fact to say that the origin of the nerves 
of rv. is nearer the fore than the hind part of that canal. Save at the price of making an 
arbitrary section, and imposing an illegal or unnatural boundary line, no one can contend 
against the Crustaceous nature of Limulus on the score of alleged subcesophageal origin 
of the antennal nerves, or those of the limbs (rrr, in the Plates of the present Memoir). 
If Dr. Anton Dohrn be not prepared to pay this price, the analogies or resemblances 
indicated by Strauss-Dürckheim, Savigny, and Latreille, of Limulus to certain Arach- 
nidans, will not suffice to outweigh the type of generative organs and extraneous 
impregnation, combined with the aquatic respiration and branchial organization of the 
present Condylopod and its palzeozoic allies. 
I fully concur with the estimable and experienced naturalist Van Beneden, that 
branchiæ of themselves may be an artificial class-character. But I cannot suppose that the 
incipient or larval relations of the nervous centres to the nerves are essentially different 
from those unquestionably demonstrable in the full-grown Limulus. The idea, therefore, of 
all the limbs succeeding the antennules (1t) being supplied from the abdominal ganglionic 
cord, must be laid to the acknowledged difficulty which Anton Dohrn met with in 
tracing out their several relations in the embryo Limulus 2-8 lines in length*, trans- 
mitted to him preserved “in strong whiskey.” Admitting, then, Limulus to be a 
Crustacean (incipient, it may be), what are its nearest allies in that class? Do the 
grounds on which I reject a ‘Trilobiten-Stadium’ at any period of its larval life meet 
with any support from affinities manifested by the adult to other Crustaceous forms ? 
Pterygotus and Eurypterus resemble Limulus in the organs of vision, save that the 
facets of the large lateral compound eyes are less distinct or less conspicuous in the fossil, 
possibly exuvial, specimens. 
Both palseozoic extinct genera manifest a clear and exclusive affinity to Limulus in the 
general proportions, modifications, and functions of the cephaletral limbs. In Ptery- 
gotus the foremost pair is chelate, the hindmost pair lamellate, the intermediate pairs are 
less differentiated and are alike. In Æwrypterus the foremost pair is the smallest and 
shortest, the hindmost the longest, and it is also lamellate. In both genera all the 
cephaletral limbs, at least all but the foremost, had the basal joints beset with ‘ carding- 
spines,’ showing their functional subserviency, as in Limulus, to the mouth as pre- 
paratory organs of digestion. 
We may consequently infer, from the analogy of the food of the living King-crabs, 
that Nereids and other soft-bodied Annelids abounded in the sandy or muddy beds of the 
old ocean in which the Merostomata + burrowed. 
* Op. cit. p. 586. $ ; 
+ This term signifies, and most aptly in its present adopted extent of application, the peculiar structure and fune- 
tion of the cephaletral limbs described in previous paragraphs. 
VOL. XXVIII. 3x 
