MYRIOPODA. 323 
ANNELID CHARACTERISTICS. 
Segmentally arranged nephridia 
as in Chaetopods. 
The muscular ensheathing of the 
body. 
The cilia in the genital ducts. 
Less important are the stump-like 
hollow legs and the simple 
eyes. 
ARTHROPOD AND TRACHEATE 
CHARACTERISTICS. 
The presence of tracheze, 
The nature of the (a tube 
with paired ostia communicat- 
ing with a pericardium) and 
the lacunar circulation. 
The modification of appendages 
uth organs. 
The form of the salivary glands. 
The smallness of the genuine 
ceelom; the cavity of the 
body is heemoccelic. 
The Onychophora differ from other Tracheata Antennata in the 
simplicity and diffuseness of the trachez, in having only one pair of 
jaws, in the absence of external segmentation, in the nature of the 
body wall, and so forth. 
The ladder-like character of the ventral nervous system (cf. primitive 
Molluscs, Phyllopod Crustaceans, and Nemerteans) is probably primi- 
tive. That salivary glands and genital ducts are homologous with 
nephridia is a fact of much morphological interest. It is possible that 
the slime glands are modifications of crural glands, and that the latter 
are homologous with the parapodial glands of some Annelids. It is 
not certain that the antennz, jaws, and oral papille of Per¢patus 
precisely correspond to the antennz, mandibles, and first maxille of 
Insects. 
Our general conclusion is that Perdpatus is an archaic type, a sur- 
vivor of forms which were ancestral to Tracheata and closely related to 
Annelids. 
Second Class of Tracheata Antennata.—MyRriopopa. 
Centipedes and Millipedes 
The centipedes and millipedes, which are grouped 
together in the class Myriopoda, are usually elongated, 
somewhat vermiform animals, with a distinct head and a 
very uniform segmented trunk. The head bears eyes 
(groups of eye-spotsAngt)¥compound eyes like those of 
insects, except in Scutigera), jomted antenne, and two or 
three pairs of jaws. The segments of the trunk bear six- or 
seven-jointed legs with terminal claws, very similar through- 
out. The nervous system, the_tr t the ex- 
cretory tubiles, etc., are like those of Insects, Tt cannot 
