304 Mr. R. Meldola on the Amount of Substance-waste 



smaller. In many species individuals sometimes fail to emerge 

 at their proper period, and then remain in the pupal state until 

 the following season. This commonly happens with Erio- 

 gaster lanestri's, and occasionally with Bomhyx quercus^ var. 

 calluncB \ I have known it to occur also with Sphinx ligustri ; 

 and my friend Mr. W. Cole informs me that he has a pupa of 

 Papilio Machaon now living (September 12th) which failed to 

 emerge at the proper period. In all cases of this kind we are 

 in complete darkness as to the respiratory activity of such 

 dormant pupfe. 



The experiments which I have now to record are extensions 

 of NewqDort's experiments* upon the loss of weight in pupae, 

 and were undertaken with a view to ascertain the exact amount 

 of the loss undergone by insects in this condition, and to 

 gain also an insight into the extent of the individual variation 

 in respiratory activity among pupte of the same species exposed 

 to the same thermal conditions. 



The first weighings made were of a specimen of Bomhyx 

 quercus found in the larval state on Leith Hill on the 2nd of 

 last June. It was nearly full-grown when found, and com- 

 menced to spin up a day or two after capture. About a week 

 was allowed to pass before making the first weighing, in order 

 to make sure that the larva had changed, and in order to 

 diminish tlie risk of error due to the drying-up of the cast-ofF 

 skin and of the cocoon. The weighings (made throughout in 

 grammes) were repeated at intervals of seven days until the 

 emergence of the imago, which took place on the 14th of July. 

 This pupa was weighed in its cocoon, and the weight of the 

 em})ty cocoon afterwards subtracted from each of the weighings. 

 The following are the results : — 



Table showing loss of weight in pupa of Bombj'x quercus during 

 periods of seven days. 



* This great physiologist proved that pupfe respired, by detecting the 

 excreted carbonic acid ; and he estimated the respirator^' activity by deter- 

 mining the quantity of this gas. The estimation of the total loss of 

 weight is essential to the present inquiiy, because water, whether produced 

 by the oxidation of hydiogen-containing tissues, or whether introduced 

 into the system with tlie juices of the food-plant, is essentially a product 

 of respiration, and counts,' like carbonic acid, for substance-loss. 



