II a The Piercing Apparatus. 



time it is the only movement necessary in the act of 

 ovipositing. Nevertheless, many muscles are required 

 to accomplish this movement. 



We pass to the examination of the other portion 

 of the terebra, the seta. The seta is only connected 

 with the two anterior plates, and like the whole ovi- 

 positing apparatus, it is throughout composed of two 

 symmetrical halves. From the upper rim of each 

 anterior plate springs what is called the arch, which 

 passes directly into, and is the origin of the seta. The 

 point where the two arches amalgamate is the origin 

 of the seta. On its lower surface, at this point, the seta 

 bears a well marked chitinous projection, called the 

 horn, which is important, because it forms the insertion 

 of a strong muscle. In consequence of its origin and 

 the way in which it is strengthened, the seta possesses 

 only a moderate degree of mobility. 



The chitinous framework of the terebra may be seen 

 when it is removed from the body, and it also comes 

 partly into view during ovipositing ; but further pre- 

 paration is necessary in order to see and understand 

 the action of these muscles. To expose them, the two 

 pairs of plates, which are firmly united and enclosed 

 in a chitinous membrane, must be separated in the 

 middle line, when the muscles belonging to each pair 

 of plates will be found placed on their inner surface. 

 In all, we have five pairs of muscles to examine. 



Beginning with the anterior plate, we see that the 

 first muscle, a very powerful one, takes its origin from 

 the upper third of the plate, and spreading like a many- 

 rayed fan is inserted by a strong tendon into the root 



