HABITS OF TWO PARASITES OF BLOW-FLIES. 



223 



is most often tliecase immediately following emergence — the male 

 hastily climbs upon the back of the female, runs forward, and grasps 

 her head with the fore-feet, usually at the lateral aspect of the eyes 

 or sometimes at the clieeks ; the intermediate feet grasp some 

 portion of the thoracic pleura, usually at the mesothorax, and the 

 hind-feet take hold along the sides of the abdomen or the edges 

 of the flat wings. The legs are not stretched out or used for 

 embracing the body of the female, but the hold is taken by the 

 feet alone, and the position of the male is not strained, but rather 

 that of the natural position of rest. His body is parallel with 

 and above the body of the female and projects beyond (cephalad) 

 it, so that the head is between -the upturned antennas of the 

 female and stretched over hers, his abdomen reaching to a point 

 above the thinl abdominal segment or to a point opposite to the 

 distal end of the marginal vein of the fore- wings, upon which it 

 actually rests. Having (juickly attained this position, the male 

 senses the antennae of the female with his own, and immediately 

 begins suit in earnest by rubbing his head up and down against 

 the inner (mesal) surfaces of the flagella of the female, which 

 are held up in a V-shaped position, at the same time holding 

 the scapes erect and apart and the flagella back, pointing laterad 

 at right angles to the scape and at every downward movement 

 bringing the scapes together ; this movement of the head is 

 accompanied by a corresponding " petting " movement of the 

 female flagella against the cheeks of the male. The up aiid 

 downward movements of the head are regular and continued for 

 from 5 to 10 seconds, each completed movement occupying 

 slightly less than a second of time ; and they are alternated with 

 a period during which the head of the male is motionless and his 

 antennae sensing those of his mate, either by touching both of 

 their tips to the tips of her antennie, or else by stroking them up 

 and down ; the mandibles, maxillie, and labium with both pairs 

 of palpi are themselves in almost constant motion, but, so far as 

 observed, they play no part as organs of sensation, witli the possible 

 exception of the maxillary palpi. Sometimes the male rubs but 

 one of the flagella of the female, turning the head to one side. 

 No other movements than these are observable, but there is some 

 variation in the occurrence of either of the two movements 

 described, and also in the number of times they are repeated 

 before sexual union is permitted by the female. The male may 

 be received coldly ; he may make the movements without 

 attempting union, or after alternating them three or four times, 

 he may attempt union without success, and then run forward to 

 repeat the actions, and this may continue as long as the female 

 permits, either resulting successfully or unsuccessfully. In the 

 presence of other females, if received coldly, the male soon tires, 

 leaves and seeks another mate. In order to attempt union, the 

 male has to reverse his position, and run back to the tip of 

 the abdomen of the female, where he usually reaches over the 

 tips of the wings and senses with the antennae, quickly turning 



