TSI FORMATION OF THE PUPA. 119 



The semi-fluid cellular matter, from which the imago is 

 developed, is derived partly from the disintegrated tissues of 

 the larva, and partly from the fat bodies or omenta. 



After the larva ceases to feed, if the temperature be suffi- 

 ciently high, the tissues begin to degenerate. The muscles 

 may be observed at this time in a state of continuous activity, 

 rythmic contractions commencing at one extremity of each set 

 of fibres, and passing regularly with a wave-like motion to the 

 opposite extremity. At the same time, large bright nuclei, 

 1-1 000th of an inch in diameter, appear in rows in the centre 

 of the muscular fibres. These are ultimately set free by the 

 degeneration and waste of the muscles, and exhibit a granular 

 appearance, but are readily distinguished by their great trans- 

 parency and low refractive power. 



At the same time a series of remarkable changes take place 

 in the fat bodied, which consist in the adult feeding larva of 

 flattened hexagonal jells filled with very opaque, highly refrac- 

 tive white granular matter. These cells now begin to exhibit 

 clear spaces in their centre, which presently become converted 

 into nuclei exactly like those formed in the muscles. The granu- 

 lar matter of the omental cell then becomes condensed about the 

 nucleus, leaving a clear space around the circumference of the 

 cell; the cells separate from each other, and the cell wall 

 undergoes disintegration. 



The free nuclei developed from the muscular fibres of the 

 larva now begin to collect around them aggregations of mole- 

 cular matter, derived from the degeneration of the muscles 

 and other larval tissues, so that all the nuclei are soon sur- 

 rounded by similar molecular aggregations, each about l-150th 

 of an inch in diameter. 



The precise nature of the changes which take place imme- 



