606 CLASS III. MYRIAPODA. 



these a protrusible sac (V.B.). The parapodia have been inter- 

 preted as the reduced posterior legs of a double segment and 

 possibly serve as sense-organs. Haase suggests that the ventral 

 sacs are homologous with the coxal glands of Chilopods and 

 that they function as respiratory organs, being often associated 

 with weak or absent tracheae. Attached to the end of the body 

 is a pair of conical processes the cerci at the ends of which 

 open the ducts of a spinning gland, the threads secreted by 

 which may be used for attaching the eggs. They are regarded 

 by Latzel as the appendages of the 24th body-segment. There 

 is a pair of stigmata on the head beneath the insertion of the 

 antennae. From each of these proceeds a strong tracheal 

 trunk which is without a spiral thickening and undergoes a 

 certain amount of branching but does not extend behind the 

 third body-segment. The alimentary canal consists of pharynx, 

 oesophagus, stomach, intestine and rectum. Two or four 

 malpighian tubes open into the intestine, and the rectum has a 

 chitinous lining. A pair of elongated salivary glands opens 

 into the mouth. The fat-body is well developed and occupies 

 the greater part of the body-cavity. There is a dorsal tubular 

 heart provided with ostia, a cephalic aorta and a ventral vessel. 

 The paired gonads are placed on each side of the gut and open to 

 the exterior by a median opening on the ventral surface between 

 the fourth pair of legs ; in the male the two testes are connected 

 by a transverse tube passing ventral to the gut. External sexual 

 characters and genital appendages are absent. The nervous 

 system consists of a supra-oesophageal ganglion and a ventral 

 chain of ganglia. The adult stage is reached by a series of 

 moults in which the segments and legs increase in number. The 

 condition of the just-hatched form is however not known. 

 The Symphyla are found in most parts of the world. They are 

 active animals and appear to prey upon small insects. They 

 avoid the light and are found under stones, etc., in damp places, 

 and in moist mould at the roots of grass. They recall Cam- 

 podea in their habits and appearance. The name Symphyla was 

 given to the order by Ryder on the view that they combine 

 insectan and myriapodan characters. They are myriapodan 

 in the number of their legs and body segments, and in the position 

 of the genital opening (Diplopoda) ; while of their insectan 

 characters attention may be called to their biunguiculate legs 



