370 bulletin: museum of comparative zoology. 



come about that the imaginal form is exceedmgly diflFerent from the 

 larval. This has necessitated great changes in the muscular system. 

 It is easy to see that iu this evolution many muscles must have reached 

 a stage where, if they were to be useful in the imago, they must be 

 stronger, or their attachments must be shifted, or they must be changed 

 iu some other manner, which would necessitate a greater or less meta- 

 morphosis. In this metamorphosis nothing could be more probable 

 than that there should be, first, a proliferation of the nuclei, second, a 

 longitudinal splitting of the original fibre into as many new fibres as 

 were needed, and, if an extensive metamorphosis was required, a de- 

 struction of the original fibrillae and the formation of new fibrillae by 

 the undifferentiated sarcoplasm remaining. Such is the metamorphosis 

 which has been described in the present paper for Coleoptera, and I can 

 conceive of nothing simpler or more probable. 



The presence of degenerating muscles is quite as easily explained. 

 In the development of holometabolic insects, it must have happened 

 many times that a muscle which was useful in the larva became function- 

 less in the imago. It is evident that the ultimate fate of such a muscle 

 would be degeneration at the end of larval life. The method of degen- 

 eration might be different iu different cases, but no one can deny suc- 

 cessfully that such muscles would exist, though Berlese has attempted to 

 do so. The converse of this might also be expected, that is, muscles 

 which are useful in the imago but functionless in the larva. Such 

 muscles would tend naturally to be retarded in their development until 

 they came to be muscles newly formed in the pupa ; but in their final 

 development they would arise from the cells which had previously 

 formed them. How it could come about that these muscles of new 

 formation in the pupa should be developed from cells furnished by the 

 degenerating muscles of other jmrts of the body, as Berlese states, is 

 something which I cannot understand. 



From what has been said, it is evident that there is little doubt as to 

 the incorrectness of Berlese's main idea in other groups of insects, as 

 well as in Coleoptera. 



Needham's ( :00) statement that the nuclei of fat cells become associ- 

 ated with the developing muscles, does not seem probable. The develop- 

 ment of such highly specialized cells into a tissue of such an entirely 

 different nature, is an exceedingly rare phenomenon. Nothing that 

 would indicate such a development has been seen in the present 

 study. 



