1903.] PACKARD—CLASSIFICATION OF ARTHROPODA. 145 
I also stated in 1893" that there are four lines of development in 
the Arthropoda (throwing out for the present the Linguatulina and 
Tardigrada), viz. : ‘‘ the Podostomatous line, the first to be struck oft 
from the Annelidan stock (the trilobites being the first forms to 
appear) ; second, the Arachnidan line; third, the Crustacean line, 
nearly coeval with the first or Podostomatous ; and the fourth, the 
line culminating in Myriopods, Scolopendrella and insects; and it 
is safe to suppose that the terrestrial tracheate groups of Arachnida, 
Myriopoda and insects were later products than the marine, 
aquatic branchiate classes—/.e., the Podostomata and the Crus- 
tacea.’’ 
Afterwards in 1898, in my Zext-Book of Entomology, as a 
result of the memoirs of Lankester, Kingsley, and the work of 
Kishinyoue on the embryology of the Japanese Limulus, from mor- 
phological and embryological data, having abandoned earlier 
opinions as to the Crustacean affinities of Limulus, I gradually 
was led to recognize the close affinity of the Merostomes and 
Arachnida, stating that the embryology of Limulus and Arachnida 
‘“ shows that they have descended from forms related to Limulus, 
possibly having had an origin in common with that animal, or 
having, as some authors claim, directly diverged from some primi- 
tive eurypteroid merostome’’ (p. 6). Again, on p. 8: ‘The 
Arachnida probably descended from marine merostomes, and not 
from an independent annelid ancestry.’’ Again, on p. 3, ina dis- 
cussion of the relation of insects to other Arthropoda: ‘It is be- 
coming evident, however, that there was no common ancestor of 
the Arthropoda as a whole, and that the group is a polyphyletic one. 
Hence, though a convenient group, it is a somewhat artificial one, 
and may eventually be dismembered into at least three or four 
phyla or branches.”’ 
Subdivision of the Arthropoda into five Phyla.—I would suggest 
the following grouping of the principal classes of the Arthropoda, 
beginning with what may be regarded as the most primitive assem- 
blage of classes, and for which I would propose the name Pa/eopoda, 
in allusion to the very primitive and homonomous nature of their 
post-antennal or post-oral appendages, when compared with those of 
1«¢ Further Studies on the Brain of Limulus Polyphemus, with Notes on its 
Embryology ” (Memoirs Nat. Acad. Sciences, p. 322, 1893). Compare also 
Zoologischer Anzeiger, April 20, 1891. 
