82 THE FLY. 



to look at, but very blood-thirsty. The flesh-fly, Sarcophaga, has 

 the singular property of hatching its eggs in its own body, and 

 bringing forth its young alive. Whilst dissecting some specimens, 

 and before I had entered upon the literature of the subject, I dis- 

 covered this. In one instance, a larva was found in the act of 

 passing the oviduct. This specimen I have mounted. 



The fact is well known. It has a good illustration in the case 

 of the green fly, one of the so-called plant-lice of the garden. A 

 still better illustration, because more easily seen, is afforded by the 

 little Daphnia, or water-flea. Neither of these is related to our 

 fly, though they agree in being viviporous, or, more correctly, ovo- 

 viviparous. But I was a witness to the fact as to the green fly, 

 which came about in this way : — I was searching webs of the 

 spider for the Polynema, and having found one, I brought away 

 with it one of the green flies. Upon examination under the 

 microscope, it proved to be alive, and struggling to get free from 

 the web. About it were other little things, much smaller than 

 itself, of a larval form, also alive and struggling. The sight was a 

 curious one, and set me thinking. I was not long, however, in 

 coming to the conclusion that I had before me a mother and her 

 offspring, and that she, small and despicable, and hated of all 

 gardeners, had the property of bringing forth her young alive. 



Forest-flies — or, as French authors term them. Spider-flies — 

 carry reproduction to a still higher development. They are para- 

 sitic on the bodies of quadrupeds. In this case, not only is the 

 larva hatched in the body of the female, but its change to a pupa 

 state takes place there also. Not until then is the egg-like form 

 deposited, and from this issues the perfect insect. But remark- 

 able as these instances are as to the reproductive faculty of some 

 insects, they are altogether eclipsed in the history of another, also 

 belonging to the Diptera, or Fly order. 



Eighteen years ago there appeared an article in a foreign 

 Journal, stating that a certain fly had been found with larvae, which 

 were not only alive, but had living larvae inside them. The article 

 had been kept back two years by the publishers, because the 

 statement " seemed almost incredible." When at last it did 

 appear, it was received with general incredulity, and declared to 

 be " a pure and simple delusion." 



