CONSIDERATIONS. 471 



the abdomen has the segments distinct, and terminates in a 

 tail, which, being articulated, appears to be the last rudiment 

 of a series of segments in a state of atrophy. In Phryniis 

 and Galeodes the body is formed of but two parts ; in the last 

 the segments are apparent, but they are not so in the rest of 

 the Arachnida. In Mygale the maxillce, with their jua/pz, 

 differ only from the feet in size, but in the other genera the 

 transformation is more complete. Nature, wishing to give 

 insects the faculty of flying, as in birds, necessarily changed 

 considerably the general form of the body from that of the 

 Myriapoda, their nearest allies. This new function required 

 that the thoracic segments should be shortened, but at the 

 same time increased in width, and also that the motion of the 

 aliferous segments should be very small or even none. There 

 is a striking resemblance between these changes and those 

 which we find in comparing the skeleton of birds and Mam- 

 711 alia. 



We find, amongst the articulated animals, ten kinds of arti- 

 culations of the teguments: — 



1. The suture, which is always harmonic, is precisely the 

 same as in the Verteh-ata. 



2. An articulation (to which M. Straus gives the name of 

 adherejice) formed by the close union of two parts by their 

 faces. 



3. Symphysis, which is only a suture in which there exists 

 a slight movement. 



4. An articulation, which may be termed linear, takes place 

 between two parts usually flat, touching by a straight margin, 

 and united by a ligament, which only allows a ginglymous 

 movement. 



5. An articulation, which may be termed syndesmoidal, 

 only differing in the ligament being very wide, which permits 

 a movement in every direction, but chiefly ginglymous. 



6. We may give the name of squamose to syndesmoidal 

 articulations, where one of the portions is so placed as partly 

 to cover the other. 



7. Enarthrosis, which resembles the same kind of articu- 

 lation in the Vertebrata, except that the soft parts in the 

 articulated animals being internal, the condyle is mostly per- 

 forated to allow of the passage of the nerves and vessels. 



8. An articulation, only differing from the last in the fact that 



