xiii, b, i Barber: The Transmission of Malaria 3 



ference between the two forms in the larva lies in the character 

 and arrangement of the clypeal hairs. In indefinitus the anterior 

 internal pair are long, the anterior external relatively short, and 

 the posterior pair very short and situated near the interior 

 pair, not directly behind these but in such a position that lines 

 drawn in a direction directly anterior to the posterior pair 

 would divide the space between the anterior internal into three 

 approximately equal parts. In type Giles the external anterior 

 pair are somewhat longer, and the posterior pair, which are 

 somewhat longer than those of var. indefinitus, lie much far- 

 ther back and are nearly directly behind the anterior internal 

 pair. Some variations in size and position occur in these types, 

 but the combination of characters is such that the observer is 

 rarely left in doubt as to which type a given larva belongs. 



While the clypeal hairs of both types are typically simple, I 

 noted various adventitious forkings and branchings, and these 

 were by far more frequent in type Giles. These branchings 

 varied from a simple forking of one of the anterior internal hairs 

 to a branching or forking of four or more hairs and sometimes to 

 a duplication of hairs. The first variation mentioned was by far 

 the most frequent. The branching was noted in mature larvae, 

 but was more frequent in young larva?. Some small larvae with 

 these adventitious branchings were isolated and examined two 

 days later, when they were found to have lost the branches. 

 Larvae were examined under a cover glass, and where there was 

 any doubt of the presence of these anomalies, specimens were 

 examined under higher powers of the microscope, in order to 

 exclude possible error from the confusion of branching with the 

 appearance afforded by the crossing of hairs. 



In 3,019 larvae of type Giles anomalies of clypeal hairs in some 

 degree were noted in 130, or 4.3 per cent. In 3,525 larvae of 

 type indefinitus they were noted in only 2, less than 0.1 per cent. 

 Possibly many anomalies were overlooked, since the matter was 

 more or less incidental to other observations, but in comparing 

 the two types, both examined in the same way and both of various 

 ages, it is evident that type Giles is more variable in this re- 

 spect. The matter may be of small weight in itself, but taken in 

 connection with the greater variability of adult type Giles, it 

 goes to show that type Giles is the less stable form. Further 

 we are put on our guard against attaching much specific or 

 varietal value to minor variations in clypeal hairs. 



