411 



described by Perez, moreover, would be difficult to interpret 

 in^terms of our usual conception of a living cell. 



(2) The Ver^tical A hdominal Muscles. 



The development of these muscles takes place in close 

 relation with the degeneration of the vertical (oblique) 

 abdominal muscles of the larva, which, as described above, 

 after losing their cytoplasm, break up into vertical fibrils or 

 groups of fibrils. While these fibrils are undergoing phago- 

 cytic destruction the myoblasts crawl along some of them and, 

 nourishing themselves aftlieir expense (fig. 110), ultimately 

 form a column of myoblasts similar to those seen in the 

 longitudinal muscles ; these on differentiating form the vertical 

 abdominal muscles whose structure does not differ from that 

 of other muscles of the abdomen. They are especially well 

 developed at the anterior extremity of the abdomen, where 

 they become attached in front to certain small phragmas 

 within the petiole, and act as the flexor and extensor muscles 

 of the abdomen. 



(3) The Dilators of the Pharynx. 



The larva possesses six pairs of pharyngeal dilators 

 (muscle fibres) to whose development I have already referred. 

 In their neighbourhood, even in the earliest larvae, can be 

 seen occasional myoblasts measuring usually some 5/x to Gju, 

 in length. 



Like the other purely larval cells, the pharyngeal dilators 

 undergo degeneration, this occurring at the time the larva 

 def aecates ; but their disintegration differs somewhat from 

 that of the muscle fibres of other parts of the body. The 

 nucleus presents the usual hypertrophied appearance, and 

 contains the gigantic nucleolus, so characteristic of the degen- 

 erating cells. As in the case of the abdominal muscles, the 

 pharyngeal dilators, after degeneration, become the prey of 

 the proliferating myoblasts of the imaginal muscles. But 

 before they penetrate the'^muscles these often undergo a 

 partial globular degeneration, and these globules, breaking 

 through the sarcolemma, are in part cast into the body cavity, 

 where they dissolve in the blood (figs. 117, 118, 119). Some- 

 times several such globules, floating about in the blood, may 

 be gathered up by a leucocyte, if one happens to be present 

 (fig. 119). 



Only a portion of the muscle fibre, however, disintegrates 

 in this way; some muscle fibres, indeed, hardly change their 

 appearance, the only indication of disintegration being the 

 refusal of the striations to absorb stains ; and between these 

 two extremes all conditions of degeneration may be observed 

 — from fibres which lose their striations but retain their 

 m2 



