I 



417 



The tendons correspond morphologically to the body 

 phragmas. They are formed as columnar ingrowths from the 

 integument, and even in the thirty-six hour pupa still have 

 an embryonic appearance. 



The tarsus is provided with a long tendon (fig. 46), 

 inserted proximally on the great tendon of the tibia, while 

 distally it is inserted on the last segment. It is not unlike 

 a tracheole in appearance; in each segment it is dilated, this 

 portion bearing the nucleus. In the first and fourth segments 

 the tendon gives off smaller branches to the walls. Only the 

 fifth segment has a muscle, which moves the claws. 



The tendon is formed as an ingrowth of cells in the 

 early pupa (six hours old) which extends right along the 

 tarsus and fuses with the tendon of the tibia. 



(6) The Muscles of the Ovipositor . 



In the female there is a remarkable development of 

 muscles in the ventral part of the abdomen, which extrude 

 and hold the ovipositor in position during egg laying. 



From the great phragma at the upper extremity of the 

 ovipositor two great systems of muscles pass to the lateral body^ 

 walls (fig. 22). From the lower phragmas other great masses 

 of muscles pass to the ventral and lateral regions of the 

 abdomen and are all so disposed as to hold the ovipositor 

 with a maximum rigidity while this is boring its way through 

 the hard shell of the fly pupa in which the insect is ovipositing. 



The mechanism of retraction of the ovipositor is very 

 simple. As already described, the ovipositor drags down the 

 sternal plate of the preceding segment during oviposition in 

 the form of a cone. On the sternum a pair of enlarged 

 longitudinal abdominal muscles from the petiole are inserted. 

 The pull which these exert on the sternal plate forces the 

 ovipositor back to its position of rest. 



The structure of these muscles is identical with that of 

 the head and leg muscles. Their development is quite similar. 



In the defaecating larva the myoblasts which have 

 throughout larval life lain in this region, proliferate rapidly 

 by mitosis. In the fresh pupa they form a solid column of 

 cells which passes right along the ovipositor; two pairs of 

 smaller columns are seen* at the sides of this column. These 

 columns then break up in the usual way, being dragged into 

 position by the adjacent in tegumental cells. Spiral stria- 

 tions appear as usual. 



(7) The Muscles of Flight. 



These are the most remarkable, and at the same time 

 morphologically the least understood, of the insect muscles. 



