B. T. LOWNE ON SO-CALLED SPONTANEOUS GENERATION. 137 



the fat bodies, which consist in the adult feeding larva of flattened 

 hexagonal cells filled with very opaque, highly refractive 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 granular 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, aud the cell wall undergoes disintegration. 



The free nuclei developed from the muscular fibres of the larva 

 now begin to collect around them aggregations of molecular matter, 

 derived from the degeneration of the muscles and other larval tis- 

 sues, so that all the nuclei are soon surrounded by similar molecular 

 aggregations, each about l-150th of an inch in diameter. 



The precise nature of the changes which take place immediately 

 afterwards are more difficult to observe, but after the second day of 

 the pupa state, numerous delicate nebulous-looking cells, about 

 1-lOOOth of an inch in diameter, replace some of these aggregations, 

 and bright nuclei, l-3000th to l-5000th of an inch in diameter, 

 make their appearance amongst them. The majority of the aggre- 

 gations remain, however, and become more dense toward their 

 circumference. The growth of the imaginal tissues* evidently pro- 

 ceeds at the expense of some of these aggregations, whilst those 

 which remain, undergo marked changes ; they increase in size, lose 

 their original nuclei, and become invested by a delicate membrane. 

 When the imago emerges from the pupa, a large number of these 

 corpuscular aggregations remain in all parts of the insect ; they 

 disappear during the development of the imago, and when it is 

 mature, not one can be detected. 



If these observations are correct, there is certainly something in 

 the process very like the development of organisms by aggregation ; 

 we find nuclei aggregating around them ; molecules, which ulti- 

 mately become invested in a membrane, and these molecules in 

 turn are capable of reproducing muscles, nerves, and other tissues 

 similar to those from which they originated. The development of 

 the perfect fly from the larva seems, to my mind, a striking proof of 

 the correctness of Mr. Darwin's theory of pangenesis, and also to 

 point to the fact, that organisms may originate in a hitherto un- 

 known manner. Even admitting that this method of origination 

 is possible, we must not conclude that such organs or organisms 



* Tissues'of the Imago or perfect fly. 



