416 



Phylum Arthropoda 



sibility of drowning. It consists of a small beaker of water inverted 

 over a semicircle of filter paper in a petri dish. [See p. 413.] 



As a food, cane sugar will support the flies indefinitely. In supply- 

 ing sugar we have abandoned our earlier use of a molar solution in favor 

 of lumps of domino sugar as suggested by Haub and Miller (loc. cit.). 



This is a vastly superior method. While cane 

 sugar alone will support the flies, the produc- 

 tion of eggs requires protein. This we have 

 supplied with fresh beef liver which also 

 provides a favorable medium for oviposition. 

 Every second day a small porcelain dish 

 16x12x3. 5 cm. loosely filled with liver, cut 

 into approximately 2 cm. cubes and moistened 

 \\/ \j with a few drops of water, is placed in the 



cage and left for 24 hours. The amount and 

 subdivision of the liver insure moist surfaces 

 in at least some crevices of the mass through- 

 out the 24 hour interval, thus permitting 

 feeding and oviposition.* 



Once the egg masses are laid, the eggs or 

 newly hatched larvae are removed from the 

 liver and placed in the gills of fish heads 

 obtained from the fish market. The fish 

 head is then placed in a wide-lipped porcelain 

 soup plate and placed in the rearing can 

 (Fig. 73)- 



The rearing can consists of a galvanized 

 pail in the lid (1) of which a circular opening 

 is cut. Into the opening a metal collar (co) 

 is soldered containing a simple damper (d). 

 Over the collar a removable cylindrical screen 

 cage (ca) is fitted. The damper permits the 

 regulation of moisture which is very important in the successful rearing 

 of larvae. If conditions are too moist the larvae leave the food and 

 migrate in all directions, a fact which must be familiar to all who have 

 tried to rear these animals extensively. 



*The species above enumerated readily oviposit under the conditions described. An- 

 other closely related species, however, Calliphora vomitoria, has failed to breed. Several 

 years ago we bred this form successfully at the Zoological Institute in Munich, Germany, 

 (Minnich, loc. cit.). Either or both of two conditions probably account for the dis- 

 crepancy. First, the culture room was cooler than our present culture room. Second, 

 fresh deer heads were readily available and these were the only medium on which the 

 flies oviposited. Half a deer head, split lengthwise, never failed to induce egg laying. 

 Unable to obtain these at will in Minneapolis, we have tried various types of vertebrate 

 flesh but invariably without success. 



Fig. 73. — Section of can 

 for rearing blowfly larvae, 

 ca, removable screen 

 cage; co, collar over 

 which screen cage slips; 

 d, damper; e, earth; 1. 

 lid of can; p, soup plate 

 culture dish; w, wooden 

 supports between plates. 



