Malacopoda— Annelids 2)73 



Malacopoda. — Opposition to the commoa origin 

 of Insects and Crustaceans from a primitive arthropod 

 stock has largely rested on the supposed near relation- 

 ship of Insects to a small class of worm-like animals, 

 the IVIalacopoda (6l, 217), comprising only a single 

 family (Peripatidz). These animals, which have a 

 remarkably discontinuous range in the tropics and 

 the southern hemisphere, have a head with a pair of 

 feelers, a pair of mandibles and a pair of papilla, 

 and a body with from seventeen to more than forty 

 segments, provided with pairs of imperfectly-jointed, 

 clawed limbs ; the skin is soft and covered with 

 small tubercles. On account of the legs, the reduced 

 coelom, and the heart with paired openings, these 

 creatures are reckoned as arthropods, but they show 

 several markedly worm-like characters — for instance, 

 a pair of kidney tubes (nepridia) in each segment. 

 They breathe by tracheal air-tubes, and, if it be 

 granted that they represent the ancestors of insects, 

 it can hardly be denied that Insects have arisen inde- 

 pendently of Crustaceans, from the original ringed 

 worms. But, as we have seen in the case of insects 

 and arachnids, tracheal air-tubes do not prove affinity. 

 Instead of regarding the Peripatidse as the survivors 

 of the ancestral stock of Insects, it is more satisfactory 

 to consider that they represent an attempt at terres- 

 trial life on the part of the very far-ofF ancestors of 

 the whole arthropod branch. They must have taken 

 to the land before those worm-like characters, which 

 became lost in the common aquatic stock of the 

 Arachnids, Crustaceans, Millipedes, Centipedes, and 

 Insects, had disappeared (215). 



Arthropods and Annelids. — A discussion of the 

 relatioQship between the whole Arthopod Branch and 

 the ringed worms (Annelida) cannot be attempted 

 here. It may be mentioned that the limbs of arthro- 



