1913] Life-History of a Bee-Fly. 219 



A third moult takes place about the time the host stops feeding 

 (late June), but in the cases observed, before the pupal cell is 

 constructed. This moult clearly takes place but the larva 

 again could not be accurately measured. 



In late June the host constructs the pupal cell {pcli of Fig. 

 16, p 221) and becomes relatively inactive but does not normally 

 pupate for a month. The parasite does not grow rapidly until 

 the host has been in the pupal cell for about three weeks. By 

 this time the old organs of the host have for the most part, 

 broken down and the internal parts are in a semifluid condition. 

 The parasitic larva now moults again and this time leaves its 

 former position completely. In the four or five cases observed 

 it moved to about the middle of the ventral side of the host, 

 (Fig. 9). It will be noted that at the time of the previous 

 moults of the parasite the host was active and if the larvae had 

 completely released its hold at any of these times the result 

 would probably have been its own destruction. At the time 

 of this fourth moult, on the other hand, the host is almost 

 unable to move. Immediately upon securing the new source 

 of food through the abdomen of the host the parasite begins to 

 grow more rapidly and more than doubles its length in 48 

 hours. The length at the time of the fourth moult is about 

 4.5 mm.; after 24 hours the length is 6.5 mm. (Fig. 9), and 

 during the next 24 hours the larva reaches . a length of 1 cm. 

 (Fig. 10), which is two-thirds the length of the abdomen of the 

 host. At the end of 144 hours the parasitic larva is full grown 

 (Fig. 11). The length is now 1.8 cm. and all of the later rapid 

 growth has apparently taken place without further moulting. 

 The full grown larva passes six or seven days in the pupal cavity 

 of the host in a quiescent stage before the pupal moult occurs. 



5. 'Pupa and Adult. 



The pupa is of the type common among the diptera. There 

 are four curved hooks upon the anterior side of the head united 

 at the base in the form of a fan (Figs. 12 and 13). Two smaller 

 hooks on the ventral side of the head appear to correspond in 

 position to the antennae. There is a circle of long stiff bristles 

 on each segment of the abdomen together with U shaped 

 bristles on the dorsal side. The pupa upon emerging is un- 

 pigmented; the hooks on the head become dark in about five 

 days; the head becomes light brown in nine days and dark 



