LIMULUS AN ARACHNID, 637 
arthropod structure, instead of being as they are descriptive 
terms devoid of homological significance. Really what Dr. 
Packard’ has to deal with is a series of segments and a 
series of appendages, and he can only compare those of one 
animal with those of another by taking them in numerical 
sequence. When an author allows himself to set up such 
intangible criteria as are involved in Dr. Packard’s distinc- 
tion between “true” and “false”? antenne, he clearly 
opens the way to any conclusion he may fancy, and may 
colour a picture as he may choose by the use of these 
epithets. 
Dr. Packard’s estimate of the significance and import of 
parts in the attempt to determine the affinities one with 
another of various Arthropods, is, it seems to me, fallacious, 
owing to the fact that it is based upon an old-fashioned 
morphology. ‘Though he makes use of the phrasevlogy of 
the doctrine of evolution, and constructs genealogical trees, 
he has “ the doctrine of types” at heart, and meets a matter 
of fact question in morphology by the use of such phrases 
as the “crustacean type,” the “ tracheate type,” and the 
*‘ hexapodous type.” With such phrases no critic can pos- 
sibly deal, for no one can say what Dr. Packard means by 
these ‘‘ types.” We are told by him that the Arachnida 
have their mandibles and maxille ‘‘on hexapodous type,” 
whilst the Merostomata (Limulus) have ‘‘only their mor- 
phological equivalents (Guathopods).” This is meant to 
appear as though a wide divergence between the Scorpion 
and King Crab were being in so many words established, 
and to Dr. Packard so it may really appear. To me it 
seems that in the statement quoted, phrases of doubtful 
meaning are being used in such a way as to vaguely assert 
the opposite of one of the most obvious facts, namely, that 
the first and second pairs of appendages of a King Crab are 
far more like the first and second pairs of appendages of a 
Seorpion than those of either are like the mandibles and 
the maxille of hexapod insects. 
Dr. Packard summarises his views as to Limulus and the 
Crustacea thus: ‘‘ The facts that seem to us to point to the 
Crustacean nature of Limulus and its allies are: (1) the 
nature of the branchie, those of Limulus being developed in 
numerous plates overlapping each other on the second ab- 
dominal limbs; those of the Eurypterida being, according 
to H. Woodward, attached side by side, like the teeth of a 
rake ; while the mode of respiration is truly Crustacean ; 
(2) the resemblance of the cephalothorax of Limulus to that 
of Apus; (3) the general resemblance of the gnathopods to 
