72 Mr. W. Sells' Observations 



XI. Observations on the Qilstridse. By the late 



W. Sells, Esq. 



Part I.— [Read October, 1837.] 



It having appeared to me desirable to extend the observations, 

 and to verify the facts which are detailed in Mr. Bracy Clark's 

 valuable Essay on the Bots of Horses and other Animals, which 

 was published in 1815, I took steps, in the spring of this year, 

 for procuring larvae of the Gastcrophili from a horse-slaughterer 

 and several horse-keepers who live in my neighbourhood ; and as 

 my applications to them have not been altogether unprofitable, I 

 beg leave to submit to the notice of the Society these first results 

 of my pursuit of this interesting department of Entomology, 



It being of considerable importance that in all inquiries into 

 the economy of insects, respecting which our present state of 

 knowledge is imperfect, we should, as much as possible, give the 

 precise dates connected with the periods of their transformations, 

 both as useful facts in themselves, and as guides to those who are 

 led to take up the same course of observation, I will first give a 

 copy of the entries in my journal which have reference to this 

 subject. 



May 12, 1837. — Received a specimen of a nearly full grown 

 larva of Gasterophilus hcemorrhoidalis, or red-tailed Bot fly ; 

 it was found in recently dropt dung, was active and lively, 

 showing no little muscular power by making a considerable 

 spring from the desk on which it was placed for the purpose 

 of being drawn while in a living state. 

 May IG. — Received three dozen of apparently full grown larvae 

 of Gasterophilus equi ; but it is probable they are all dead, 

 in consequence of their close stowage in the pill-box provided 

 for their reception (as afterwards proved to be the case) : 

 also one larva of hcemorrhoidalis, which had been plucked 

 from the verge of the anal passage. 

 June 25. — Received three larvae o{ hcemorrhoidalis which appear 

 full grown, and will most likely go into pupa ; the man who 

 sent them said there were two more adhering to the horse's 

 rectum, which he had tried carefully to pull off, but their 

 heads were separated in the attempt, the others had dropped 

 in the dung. 

 June 27. — Received a larva which I considered at the time to 

 be one of G. equi, but it turned out afterwards to be G. vete- 

 rinus, and a female. 



