LIMULUS AN ARACHNID. 509 
Limulus is concerned in spite of Packard’s recent work-in 
that direction (9) ; in fact, the comparative anatomy of the 
nervous system of Arthropoda generally has yet to be placed 
on a firm histological basis, and until this is done we must 
not attach a very great importance to the results of simple 
dissection. With regard to the naked-eye appearance of 
the nervous system of Scorpion, we have, however, the 
exceedingly careful work of George Newport (6), which is 
worthy of all confidence, and what is of more importance 
we have certain embryological data furnished by the investi- 
gations of Metschnikoff (21) and of Balfour (20). The 
observations of the latter zoologist relate to the Araneina, 
but may fairly be considered as confirmatory of those of 
Metschnikoff. 
The central nervous system of Limulus consists, according 
to M. Alph. Milne-Edwards, (A) of a distinctly emarginated — 
brain or cerebral mass which I have elsewhere proposed to 
call the ARCHI-CEREBRUM,! and of two strands of nervous 
tissue, which embrace the cesophagus and unite behind it, so 
as to form (B) an oval aisOPHAGEAL COLLAR, being continued 
backward from their point of union along the ventral surface 
of the animal as (c) the ABDOMINAL CORD to a point some 
distance in front of the anus. The limbs of the collar are 
united by from three to eight transverse commissures in 
front of their point of union with one another and behind 
the esophagus. From the archi-cerebrum are given off five 
nerves only, namely, those to the ocelli, to the compound 
eyes, and to the frontal integument. From the esophageal 
collar a great number of nerves radiate, including those to 
the first as well as to all the other pediform appendages, 
and also the nerves to the chilaria (or metathoracic sternites) 
and to the genital operculum. We find a distinct nerve to 
each appendage, and a number of large tegumentary nerves 
also given off from the cesophageal collar. It is important to 
note that the pair of nerves to the genital operculum is 
derived from this region and not from the cord-like prolonga- » 
tion of the united strands of the collar. It is also important _ 
to observe that at present we have no knowledge of the exist- 
ence of distinct ganglia or enlarged masses of nerve-cells in 
the esophageal collar, so that it is not possible to infer from 
any such fact of strifcture how many ganglia corresponding 
to an equal number of segments are represented by the 
cesophageal collar. M. Alphonse Milne-Edwards, who holds 
the ‘‘chilaria” to be the equivalents of the Scorpion’s “ pec- 
1 This Journal, April, 1881. ‘On the Appendages and on the Nervous 
System of Apus cancriformis,’ 
