﻿88 LUCIUS NICHOLLS — THE TRANSMISSION OF PATHOGENIC MICRO- 



ORGANISMS BY FLIES IN SAINT LUCIA. 



hatched larvae. This appears to have do effect upon the growth and development 

 of the host until it pupates, when the egg hatches and the resultant guest larva 

 undergoes its development at the expense of the pupa. In a number of cases 

 the period of time from laying the egg to the emergence of the Hymenopteron 

 varied from 22 to 28 days. On one occasion 500 pupae of the three Tachinid 

 flies mentioned above were placed in a vessel and 126 female Chalcididae 

 hatched out. 



I have seen a female Chalcid seize a larva of a Sarcophaga by her hind legs 

 (fig. 5) and with extreme rapidity arch her body and insert her ovipositor. The 

 egg is now laid (not down the ovipositor) and by means of two mobile organs in 

 connection with the ventral plate, the Chalcid manipulates at the spot pierced by 

 her ovipositor ; apparently this is for the purpose of guiding the egg to its 



Fig. 5. — Chalcid ovipositing in larva of Sarcophaga. 



situation. The egg reaches the interior of the host by its own action. In form, 

 it is pear-shaped, with a ductile stalk having a slightly knobbed end. When the 

 egg is first laid the stalk is bent and curved back upon the egg ; held and guided 

 by the organs above mentioned it reaches the spot pierced ; now the stalk springs 

 out and enters the hole made in the maggot ; the contents of the egg gradually 

 travel down the stalk to the knobbed end, and thus, as it were, the egg flows 

 through its own case into the interior of the maggot. I have arrived at this 

 conception of ovipositing from the following facts which I have observed : — 

 (1) Fly seizing maggot and piercing it with its ovipositor — sometimes ifc pierces 

 the maggot in the interior of the faecal matter ; (2) egg bent upon itself and 

 resting on the two organs above mentioned ; (3) egg released and straightening 

 and stiffening itself in a very life-like manner ; (4) maggots with an egg attached 

 to a segment, the end of the stalk being apparently embedded ; (5) the egg 

 gradually becoming smaller, as it is observed under the microscope attached to a 

 maggot. 



I have attempted to indicate a large and absorbingly interesting field of useful 

 study, which can be derived from flies which breed in very noisome and objection- 

 able surroundings ; probably their breeding places have caused insufficient 

 attention to be paid them. 



Castries, Saint Lucia. 



