ir STRUCTURE OF SVMPHVLA 6 I 



Order IV. Symphyla. 



We next come to one of the last two Orders which have 

 been recently added to the Myriapoda. These little animals 

 have a great resemblance to the Thysanura among the Insects, 

 and especially to Campodea among the Thysanura. It will be 

 well, therefore, to begin our account with a few of the reasons 

 which have induced naturalists to include them among the 

 Myriapods rather than among the Thysanura. 



1. Campodea has three pairs of mouth appendages, while 



Scolopendrella has only two. 



2. Scolopendrella has broad plates covering the back, not only 



on the anterior (thoracic) segments, but on the whole 

 body. 



3. The terminal appendages of Scolopendrella differ from 



those in Campodea. 



4. Scolopendrella has a sense organ which is absent in 



Campodea. 



5. Campodea breathes by means of three stigmata in the 



anterior part of the body. The stigmata of Scolopen- 

 drella are hard to see, and -are not in the same position. 



6. Scolopendrella has twelve pairs of legs, and Campodea, like 



all Insects, has only three. 



I will now go on to an account of their anatomy. The body 

 is small and slender, and is covered with a delicate shell or exo- 

 skeleton of chitin, which is so thin as to be almost transparent. 



The antennae are long, and are composed of many joints of 

 equal size. 



The mouth parts consist of 



1. An upper lip. 



2. A pair of mandibles. 



3. A pair of maxillae. 



The segments are not all of equal size. Some are larger than 

 others. The larger and smaller segments are arranged alter- 

 nately, and the smaller do not bear legs. As before stated, there 

 are twelve leg-bearing segments. 



At the end of the body there are two hook-like appendages 

 which are pierced by a canal, through which is poured the secretion 

 of a pair of glands. Near the sides of these appendages are a pair 

 of sense organs, consisting of long hairs connected with nerves. 



