ARTHROPODA 



297 



Annelida and the higher arthropods. They are remarkable for a wide distribu- 

 tion out of proportion to their numbers, and are found in moist places, under 

 wood, stones, and in rotting bark. They agree with the chaetopod annelids 

 (see §276) in the possession of segmental organs (nephridia), a dermo-muscular 

 sac, and poorly developed appendages. The segments are also homonomous 

 (see §264) as in the worms. The relationship to arthropods is indicated by the 

 possession of tracheae, by the substitution of haemoccele (the enlarged lacunae in 



Pig. 



Fig. 13s. Caprella geometrica. From Verrill. X 4. 



Questions on the figure. — In comparison with other Crustacea what are the 

 aberrant or peculiar features of this form? See also figures in reference texts 

 (e.g., Parker and Haswell's Zoology, Vol. i, p. 546). 



which circulation occurs) for the true ccelom, and by the differentiation of some of 

 the anterior segmental appendages as mouth parts. The Onychophora resemble 

 the larval condition of those insects which undergo a metamorphosis much more 

 than the adult stages. This suggests that they are more closely related to the 

 ancestral types from which the insects have sprung than to the insects themselves 

 (Pig. 136). 



Class III. Myriapoda {many feet; Centipedes, etc.). — Trachea te arthropods 

 with a worm-like body. Segments numerous, and much alike, one (or, in Dip- 



FiG. 136. 



Fig. 136. Peripatus capensis. From Nicholson after Moseley. 



Questions on the figure. — Externally in what respects is this form like the An- 

 nelids ? In what respects different from them ? Of what special zoological interest 

 is this genus? What are its habits? In what respects is it like and in what unlike 

 the centipede (Pig. 137)? 



lopoda, two) pair of appendages to each segment. The head is distinct and bears 

 antennae and mouth parts. The eyes are numerous and simple {ocelli). In 

 fundamental structure and development the myriapods resemble insects. There 

 are two principal orders. One embraces the centipedes (Pig. 137) which are car- 

 nivorous, have biting jaws, have one pair of appendages to each segment, and are 

 poisonous. The second includes the millipedes which are vegetable feeders and 

 possess mandibles suited to chewing vegetable matter. They are wholly harmless. 

 They have two pairs of legs to each of the numerous segments except the first four. 



