44 Observations on Parasites and Parasitic Diseases 



The sides of the pupa are somewhat flattened, and are marked 

 Avith twelve distinct depressions, arranged in two parallel lines. 

 „ ^ Occasionally these depressions are more 



strongly developed on one side of the pupa 

 than on the other. They are described 

 as being connected with minute apertures 

 for the transmission of air to the growing 

 embryo ; but we have never been able to 

 satisfy ourselves by an examination of the 

 pupa cases, either before or after the escape 

 PupaoftheMelophagus. ^^ ^he young Melophagi, that they had 

 Magnified. ^"J such connection, or indeed that there 



is any opening whatever. From the cen- 

 tral part of the truncated extremity of the pupa a small pro- 

 jection rises (see fig.), which has a well developed spiracle on 

 each side of it. These openings would appear to be the chief, 

 if not the only means by which air can reach the embryo. 



In an early stage of the development of the pupa, a similar 

 projection is to be noticed at the rounded extremity, giving 

 attachment to a slight membranous thread — the umbilical cord 

 — by means of which the pupa is connected to the oviduct. In 

 some pupae this projection remains long after their expulsion by 

 the parent, but it rarely persists for so long a time as the one at the 

 opposite end. The young Melophagus when perfected makes 

 its escape at the rounded extremity of the pupa case by raising 

 it as an operculum at the place marked by a line in the figure. 



The time which is occupied in maturing a pupa within the 

 body of the parent seems not to have been ascertained ; but seeing 

 the rapidity with which Melophagi increase during the summer 

 months, we conjecture that it cannot be very long. Repeated 

 experiments enable us to express our belief that about fourteen 

 days elapse between the birth of the pupa and the perfecting 

 and escape of the young Melophagus from it. We cannot, 

 however, speak with absolute certainty upon this point, in con- 

 sequence of the difficulties in the way of its correct solution. 

 It seems to be necessary for the development of the embryo 

 that the pupa be kept not only warm, but protected to a con- 

 siderable extent from the drying effects of the air, conditions 

 which are provided for by its lying near to the roots of the 

 wool, and being smeared over with the sebaceous secretion 

 of the skin of the sheep. When pupae are removed from 

 the wool for experimental purposes, and kept at about the 

 same natural temperature, the nearly perfected embryos will 

 often make their escape in four or five days. After this time, 

 under ordinary circumstances, the embryos mostly die, so that the 

 shepherd has it^in his power to destroy many Melophagi by 



