BREED: METAMORPHOSIS OF THE MUSCLES OF A BEETLE. 341 



on Coleoptera will be spoken of first, and in greater detail than those on 

 the other groups, as they are of more interest in connection with this 

 paper. None of the researches on Coleoptera had, as a main object, the 

 study of the muscular changes, and most of the investigators speak of 

 them only incidentally. 



Coleoptera. The first paper in chronologcial order is that of Rengel 

 (*96), who describes the changes which occur in the midiutestine of 

 Tenebrio during metamorphosis, including a description of the changes 

 of the intestinal muscles. The muscle layer of the larval intestine de- 

 generates into a structureless protoplasmic zone in the late larva and 

 early pupa. In this protoplasmic zone the individual muscle fibres can no 

 longer be distinguished, though the nuclei of the larval fibres remain 

 unaltered. No phagocytes (" Korachenkugelu " of Weismann, '64) are 

 present, this degeneration being entirely chemical. The intestinal mus- 

 cles of the imago develop in this protoplasmic zone, but the exact 

 method of their formation is somewhat in doubt. Apparently, part or 

 all of the nuclei of the larval muscles remain and form the new muscles 

 out of the material in which they are embedded. 



De Bruyne ('97), speaking of phagocytosis in the development of in- 

 vertebrates, treats of the changes in the hypodermal muscles of Tenebrio 

 during metamorphosis. He finds a degeneration of the larval muscles, 

 which begins with a chemical alteration of the muscle substance. The 

 muscles soon break into fragments, which later are engulfed in leucocytes 

 acting as phagocytes, thereby forming " Kornchenkugeln." These mus- 

 cle fragments undergo fatty degeneration in the phagocytes, each becom- 

 ing surrounded by a vacuole. Tlie vacuoles with their contents fuse 

 with one another until each phagocyte contains a few large vacuoles 

 with correspondingly large fat globules .inside. These fat globules are 

 then dispersed to the growing tissues, leaving the large vacuoles in the 

 cytoplasm of the phagocyte. This is the beginning of degeneration for 

 many of the phagocytes. 



Krtlger ('98), describing the development of the wings in beetles 

 (Tenebrio, Lema), states that he finds two larval muscles at the base of 

 the wing (the flexor alae metathoracis, judging from his figures) which 

 metamorphose into wing muscles of the imago. He concludes from this 

 that the wing muscles of the adult are metamorphosed larval muscles. 

 He also finds in the blood what he calls " Weismannsche Korncheu- 

 zellen." 



In an article on the anatomy and metamorphosis of the intestinal 

 canal of Auobium, Karawaiew (*99) states that there is no phagocytosis 



