214 DISEASES OF INSECTS. 



it is a malady of no great importance. Lastly, some- 

 times the mulberry leaves have a gummy rather acrid 

 secretion, which purges the silkworms; their excrement 

 is no longer solid ; they become weak and languid ; and 

 if the secretion is abundant, their transpiration is impeded, 

 and at the time of moulting they are become so feeble as 

 to be unable to cast their skin a . 



In the case of many caterpillars of Lepidoptera that 

 died, Bonnet found by dissection that the disease was 

 remotely occasioned by a diarrhea, which taking place 

 immediately before they became pupae, prevented the 

 inner membrane of their intestines from being rejected, 

 as it would have been if no extraordinary cause had 

 prevented it, attached to the hard excrement. He found 

 this membrane converted into a jelly occupying great 

 part of the stomach, which he conjectured was the proxi- 

 mate cause of their death b . 



To conclude this head spiders are reputed to be sub- 

 ject to the stone : I do not say Calculus in Vesica ; but 

 we are informed by Lesser that Dr. John Franck hav- 

 ing shut up fourteen spiders in a glass with some vale- 

 rian root, one of them voided an ash-coloured calculus 

 with small black dots . 



II. I now come to that class of diseases which appears 

 to prevail almost universally amongst insects I mean 

 those resulting from the attack of parasitic enemies. 

 Thus millions and millions annually perish before they 

 have arrived at their perfect state. Diseases of this kind 

 proceed either from vegetable or animal parasites. I shall 

 begin with the first, which will not occupy us long. 



i. As insects pass often no small portion of their life 



a Latr. Hist. Nat. xiv. 163. N. Diet. d'Hist. Nat. iv. 134. 

 b GEuvr. ii. 48. c Lesser L. ii. 121. 



