the Excrement of Insects. 31 



in a letter which I had the honour to address to you in April, 

 1851, and which was published in the Transactions of the Ento- 

 mological Society for the same year. 



GO. Of a Musca lanio the anal portion was cut off, and digested 

 in dilute nitric acid ; the solution formed, carefully heated gave 

 a distinct trace of lithic acid in the color produced. 



61. A Musca domestica, similarly treated, afforded a like re- 

 sult. 



62. A Musca slahulans, the like. 



63. A fly {Hcteromyza huccata) yielded a very slight trace of 

 lithic acid, requiring microscopic examination to distinguish the 

 color. 



64. An Eristalis lenax afforded a slight but yet a distinct trace 

 of the acid. 



On these, the preceding observations, having now described 

 all I have to offer, I would beg to make a {"ew remarks in con- 

 clusion. 



Considering the properties of the excrementitious matter exa- 

 mined, I apprehend it may be admitted that in almost every 

 instance a part of it, and in most instances the larger portion, was 

 urinary, — a renal secretion. 



Adopting this conclusion, the urine of the insects in their earlier 

 stage, their larva state, would appear to differ considerably from 

 that of the same insects in their imago or perfect form. Thus, whilst 

 in the latter it was found to consist chiefly of lithate of ammonia, in 

 the former lithate of ammonia was sparingly detected, or not at all ; 

 what seemed to be hippuric acid being more abundant. Should 

 further inquiry be confirmatory of this, will not an interesting 

 analogy be established, viz. of one, the perfect insects, in their 

 urinary secretion, to birds, which they resemble in so many other 

 particulars ; of the other, the insects in their larva state, in rela- 

 tion to the same secretion, to the mammalia, to which also, espe- 

 cially in their mode of feeding, they bear a certain resemblance — 

 a resemblance that may be traced through several orders, accord- 

 ing to their diet? Even in their transition state, that is, when 

 passing from the larva to the imago, comparing the pupa of the 

 insect with the excluded ovum of the bird, the analogy seems to 

 be sustained — both, in the process of hatching to evolve the perfect 

 animal, being independent, with the exception of atmospheric air, 

 of any external material supply. The renal secretion of the foetal 

 bird is, I believe, always lithate of ammonia; at least, I am not 

 aware that any other has yet been detected. In the insect we 

 have seen how, when fully formed and quitting its puparium, the 

 same compound has abounded. 



