C14 ZOOLOGY sect. 



limbs. The nephridia on the other hand, and their modification 

 in certain segments to form the gonoducts, which are ciliated 

 internally, are annulate in character ; and in all probability the 

 slime-glands and coxal glands correspond to the setigerous glands 

 of the Chastopoda. The nervous system is peculiar, and is most 

 nearly paralleled among the Platyhelminthes and the Mollusca. 

 Also peculiar, and serving to distinguish Peripatus from the rest 

 of the Arthropoda, are the large number of stigmata and their 

 irregular arrangement, the presence of only a single pair of jaws, 

 and the nature of the cuticle. 



CLASS III.-MYRIAPODA. 1 



The class Myriapoda, including the Centipedes and the Millipedes, 

 consists of tracheate Arthropoda, which present many features 

 of resemblance to the Insects. There is a distinct head, bearing 

 many-jointed antennas, a pair of eyes, and two or three pairs of 

 jaws; the body is not distinguishable into regions, but consists 

 of a number of similar segments, each bearing either one pair of 

 legs or two pairs. A system of air-tubes or tracheae, similar to 

 those of Peripatus and the Insects, open by a series of stigmata, 

 usually in considerable numbers, on the sides or lower surfaces of 

 the segments. 



A. — Distinctive Characters and Classification. 



The Myriapoda are tracheate Arthropoda in which there is a 

 head, bearing antennas and jaws, and a trunk made up of a number 

 of similar segments, provided with leg-like appendages. Groups 

 of ocelli are present on the head. 



Sub-Class I.-PROGONEATA. 



Myriapoda in which the genital apertures are situated far 

 forwards towards the anterior end of the body. 



Order 1. — Pauropoda. 



Progoneata with ten trunk-segments and nine pairs of legs, one 

 pair to each segment except the first. Antennas with several 

 nagella. Tracheae not known. The order includes only the single 

 genus Pauropus (Fig. 489). 



1 As will appear subsequently, the class Myriapoda, as formerly understood, 

 comprises two groups which are separated from one another by such important 

 differences that they might very well be looked upon as constituting two distinct 

 and independent classes. The old class Myriapoda is retained here as a matter 

 of convenience, and the two constituent groups are ranked as sub-classes. 



