120 



course of experiments, so there is no positive evidence as to whether 

 the larva of the worm is passively liberated by the digestion of the 

 fly, or. whether it escapes prior to such digestion, though probably 

 the former is the case. Once freed from the fly-host in the stomach 

 of the horse the larvae of H. muscae and H. microstoma develop in the 

 stomach contents, and retain their hold by inserting their heads into 

 the mucous membrane, or at least into the lumen of the glands. 



The second part of the paper deals with investigations on certain 

 points in the hfe-history of Melophagus ovinus, L. (sheep louse-fly or 

 sheep-tick) undertaken in view of the fact that the enforcement of the 

 Sheep Dipping Act has not had the effect of eradicating this pest. 

 Unlike the true ticks, which leave their host to oviposit, this Hippo- 

 boscid fly spends its whole life upon its host, the nearly mature larva 

 being extruded into the wool, where it forms a puparium that is securely 

 attached to the fleece by a glutinous substance. The pupal stage 

 varies according to temperature. On sheep kept in a stall in winter 

 (43° F. to 47° F.) the period was found to be from 22 to 24 days, 

 while in summer (47° F. to 72° F.) it was from 19 to 21 days. Young 

 female flies are capable of pairing 5 days after emergence from the 

 pupae, and the first pupa is extruded 13 to 23 days after emergence, 

 but the length of life of, and the number of pupae extruded by, an 

 individual female have not yet been determined. Pupae appear to 

 be extruded, for a time at least, at an average rate of 1 every 

 9 days. 



The period of viability of M. ovinus when removed from the host 

 and kept without food is longer under Southern Australian conditions 

 than those obtaining elsewhere. European and American investigators 

 have stated that it does not live to the 8th day, and that most indivi- 

 duals die in from 2 to 4 days. In Victoria however they were kept 

 alive of? the host for llf days under cool, uniform conditions in early 

 summer. [See this Review, Ser. B, vi, p. 42.] The adult lives longer 

 apart from the host than does either the unfed insect under one day 

 old, or the young insect of 3 to 7 days old that has fed upon the host. 

 The longest period for which an adult female has been kept off the 

 host and without food is up to the 18th day. 



Except under extreme temperatures, a certain proportion of the 

 pupae are viable for periods var}dng up to 42 days after removal 

 from the host. This fact shows that there is some slight ground for 

 the contentions of those sheep owners who maintain that sheep pre- 

 viously freed by dipping may become reinfested from individuals 

 left on grass, bushes or posts, or with those that emerge from pupae 

 dislodged from the fleeces of infested sheep, either by rubbmg or by 

 the dipping fluid or heavy rain dissolving the glutinous matter at- 

 taching them to the wool. Even under favourable conditions however 

 the numbers that survive for more than 4 or 5 days off the host and 

 subsequently re-infest clean sheep must be extremely small, much 

 too small to account for a general re-infestation of a clean flock or 

 even a moderately large part of it. The author concludes that most 

 of the parasites found on previously dipped sheep are the progeny of 

 pupae extruded prior to dippmg, which escaped the destructive 

 action of the fluid. All the sheep used by him experimentally had to 

 be dipped twice, even though strong solutions were used for the first 

 dip, such as cyllin, in the proportion of 2 oz. to 1 gal. water. 



