208 J. W. SCOTT MACFIE. 



been suggested, the mosquitos after their first feed bite only during the hours of 

 twilight or in the dark. From individual cases, such as experiment No. ii., some such 

 conclusion might have beeii drawn ; but a careful examination of the w^hole series 

 showed that it would have been quite inaccurate. 



In the case of the initial feed it might have been supposed that a preference for some 

 particular hour w^ould have been shown, since this feed precedes the laying of the 

 first eggs. It was found, however, that the mosquitos took this first meal of blood 

 sometimes by dayhght, sometimes in the dark ; in the early morning, in the middle 

 of the day, or at night, and that no preference seemed to be evinced for any particular 

 hour. In one experiment (No. viii) an unfertihsed female w^as kept for 35 days. 

 During this time she fed on blood ten times, and on each occasion at night. 



Ovulation. 



The first batch of eggs was generally laid on the sixth or seventh day ; that is three 

 or four days after the first meal of blood. The actual number of eggs laid in each 

 batch varied greatly, sometimes about a hundred being deposited, sometimes as few 

 as seven. The majority of the batches were found in the early morning, between 

 6 and 7 a.m., the hour at which the mosquitos were first looked at each day. As by 

 this time the mosquitos were as a rule ready to feed on blood, it is probable that they 

 had finished laying their eggs some httle time previously. Over fifty per cent, of the 

 eggs laid in the course of the experiments were deposited before 8 a.m. If the eggs 

 w^ere not laid at this time they were generally found in the evening or late afternoon. 



After the first blood feed the females were found to lay their eggs at regular intervals 

 up to, or almost up to, the day of death, provided that they had previously been 

 fertilised, and that every opportunity was given them of feeding on blood whenever 

 they wished. Each batch of eggs was laid three or four days after each blood feed. 

 Under such circumstances the number of batches of eggs laid depended on the length 

 of the life of the mosquito. One female of my series laid fifteen batches in her fife of 

 50 days ; but as it is recorded that Stegomyia fasciata may live much longer than this 

 there seems no reason to suppose that a much larger number may not sometimes be 

 attained. The statement made by Boyce (1911) that "The average number of 

 separate batches of eggs laid by a single female may be given as two to three, but that 

 as many as nine batches have been laid in some cases " is certainly an underestimate. 



In order that eggs may be laid it is necessary that the female should be first 

 fertilised, and then allowed a meal of blood. An unfertihsed female lays no eggs, 

 although she may feed on blood repeatedly. This fact is illustrated by experiment 

 No. viii., in which an unfertilised female fed on blood ten times during 35 days, but 

 laid no eggs. The mosquito, however, retained her power to lay eggs ; and after a 

 male had been introduced into the jar in which she was confined, she laid, on the 

 43rd and 45th days of her life, eggs from which larvae hatched a few days later. It 

 has been shown by Goeldi that fertilised eggs may he dormant in the female for as 

 long as 102 days, and may then be laid if a feed of blood is allowed ; and experiments 

 Nos. iv. and v. show the same postponement for shorter periods. It is clear therefore 

 that both fertilisation and blood are necessary to the female for ovulation. But it 

 is not necessary that fertilisation should take place immediately before or after the 

 blood feed. In experiment No. vi. fertile eggs were laid 24 days after the last male had 



