56 



these became elongated, and put on the appearance given in 

 c c c. Their tops' now began to enlarge as in d, and gradually 

 assumed the form e e. There were two divisions in these elon- 

 gated cylinders, the one across the neck, g, and the other lower 

 down at h, the cell between these divisions, g and h, being filled 

 with granular matter. As soon as they had assumed their com- 

 plete form, circulation commenced in an oblique direction round 

 the head. It gradually quickened, and the heads were finally 

 driven off with violence by the bursting of the middle cell, g h, 

 and were projected in every direction. They adhered strongly 

 to whatever they touched, being surrounded with a viscid gummy 

 matter from the bursten cell, as in fig. 3, and it is to their 

 agency that the frosted appearance of the glass is due. Thus 

 so many were driven off against the object-glass as to render it 

 quite dim : I accordingly cleansed them off, and interposed a piece 

 of thin glass to receive them, and thus enable me to ascertain 

 their nature and form. 



In fig. 4, I have represented one of these heads, with a portion 

 of the bursten cell. Fig. 5, gives their size, being about T*-oi>th 

 of an inch ; i i, represents the misty appearance produced by 

 their agency. 



This disease is remarkably rapid in its development, for the 

 whole time tha| elapsed from the death of the fly to the ripening 

 and projection of the heads was not more than three hours. 



The heads being always driven off whole, as in fig. 3, would 

 lead us to suppose that they were seed-vessels, but I can give 

 no opinion as to whether the disease is propagated from them 

 or from the disrupted cells. 



I do not believe this to be any casual or accidental mildew 

 consequent on a disease, but the disease itself, for it always puts 

 on the same appearance, and as it always commences in the 

 proboscis, and as the death of the fly occurs before there is 

 any appearance of the growth of these white cylinders, we may 

 infer that the matter by which they are produced is highly poi- 

 sonous. 



Having thus satisfied myself as to the usual progress of this 

 disease, I tried an experiment with these cylinders : I put some 

 of the flies, in which this appearance had commenced, under water. 

 In this case a considerable alteration took place, the cylinders no 

 longer producing heads as before, but growing thin and crooked, 

 like fig. 0. 



