Insects ' and Pat -as i tic D Iseases. 3 5- 



micrograpliic Figs. 34 and 35 show larvae escaping in both ways. 



It seems possible in view of the above facts and the well known 

 piercing power of the proboscis in Stomoxys calcitrans that the 

 failure of the specimens to pierce the skin in the above experiment 

 was due to the proboscis being clogged by the larval parasites, 

 twelve in one case and fifteen in the other. 



'G. To determine whether from a mixed infection of Habronema 

 muscae and Habronema microstoma in sterilized faeces 

 any selective action is present between the parasites and 

 a particular species of intermediate host. 



All the evidence adduced as a result of the experiments and 

 •observations recorded in the preceding pages of this report is in 

 the direction of establishing the fact — (1) that Habronema muscae 

 has Musca domestica for its only intermediary host, (2) that H. 

 microstoma has Stomoxys calcitrans for its principal intermediary, 

 (3) that Musca domestica may act, very rarely and in small measure 

 ■ — under experimental conditions, at any rate^ — as an alternate 

 intermediary host for H. microstoma. 



It appeared desirable therefore to carry out further experiments 

 to determine the selective activity (if any) shown by Habronema 

 embryos of a particular species for a particular species of inter- 

 mediary, and especially the relationship of Stomoxys calcitrans to 

 Habronema musca and the relationship of Musca domestica to 

 Habronema microstoma when given a free choice. With this object 

 in view the following experiments were carried out : — 



ETperiment No. 15. 



On January 21st embryos from three gravid females of H. muscae 

 and H. microstoma were liberated in sterilized faeces, and on the 

 following and subsequent days larval Musca domestica and 

 Stomoxys calcitrans, then three days old, were fed upon the in- 

 fected nxatter. The first 28 Musca domestica flies emerged on 

 February 4th, of which 15 were infected and 13 were free from 

 parasites, the number of parasites in infected flies varyin<i; from 

 one only in each of seven flies to four in each of three flies. 



The first six Stomoxys flies emerged on February 11th, all of 

 which were found to be heavily infected, i.e., not less than 60 

 parasites in eacli. Details and measui-ements of some of tliese 

 larvae are given in Tables 5 and 6. 



In Tabl^ 5 particulars are given of six larvae from Musca 

 domestica flies (February 4th). The measurements of specimens 



