386 SYNOPTIC COLLECTION. 



SYMPHYLA. 



The Symphyla is represented by the interesting little 

 Scolopendrella (PI. 944, fig i, enlarged; natural size indi- 

 cated by vertical line) which Ryder considers may be the 

 last survivor of an ancestral form from which insects 

 have descended. It is a synthetic type, combining char- 

 acters of Myriopods and Insects, the insectean features 

 predominating. 



The body of Scolopendrella consists of a limited num- 

 ber of segments which have the appearance of plates on 

 the dorsal side. The head (PI. 944, fig. i ; fig. 2, ven- 

 tral side, enlarged) is distinct and movable. Twelve of 

 the segments bear jointed legs that terminate in two 

 claws instead of one, as in the Myriopods. 



The antennae (fig. 2) are longer than those of Myrio- 

 pods and in structure are essentially different. They 

 resemble a series of glass cups strung upon a delicate 

 rod (Wood-Mason). There are a pair of mandibles and 

 two pairs of maxillae, the two parts of the second pair 

 uniting to form a lower lip or labium. The first two pairs 

 of mouth parts are not fastened to the head or skull by 

 a hinge joint as in Myriopods and most insects, but are 

 withdrawn into the head and are buried in the muscles of 

 the mouth, so that only the tips appear outside. 1 



The appendages of the last segment are modified into 

 organs called cerci (fig. 2) ; at the end of each of these 

 is the opening of the silk glands, the ducts of which can 

 be seen in fig. 2. At the bases of the legs there are 

 movable vestigial ones (fig. 2) which probably represent 

 the second pair of legs similar to those found in Diplo- 

 poda. 



The internal organs are similar to those of insects. A 

 small pair of spiracles are situated in the front of the 



1 Packard, Amer. Nat., XV, 1881, p. 701. 



