METAZOA INSECTA. 489 



in masses of various shapes and the young larvae (fig. 2) 

 are extremely active. They breathe by means of a 

 respiratory tube which extends to the surface of the water, 

 as seen in fig. 2. According to Howard the organs at 

 the end of the abdomen called gill flaps (see No. 1252, 

 species unknown) may be respiratory in the young larva 

 but later are probably locomotor organs. These are 

 seen more plainly in the full grown larva (PL 1251, fig. 3). 

 The development is accelerated and when seven days have 

 passed the larva becomes a pupa (fig. 4). In this stage 

 it remains quiet at the surface unless disturbed when it 

 moves by means of the muscles of the abdomen. It is a 

 most peculiar looking insect on account of the swollen 

 thoracic region. It breathes now by means of two tubes 

 on the thorax seen in No. 1252. The pupal stage is 

 only two days long when the adults (No. 1253 ; PI. 1251, 



% 5> <?; fi g- 6 > ?) emerge. 



The genus Anopheles is of especial interest on account 

 of the part it plays in the transmission of disease. It 

 has been discovered that the malaria germ is a Protozoan 

 which lives as a parasite in human blood. When Ano- 

 pheles maculipennis bites a person infected by this para- 

 site it sucks up into its own body the malarial germ which 

 in a short time undergoes a true sexual development. 

 The fertilized parasite ultimately passes into the proboscis 

 of the mosquito and is injected with the poison into the 

 next person the insect bites, who thereby becomes a vic- 

 tim to malaria. While the larva of Culex is usually seen 

 in the position represented in PI. 1251, fig. 2, the larva of 

 Anopheles rests in a nearly horizontal position just beneath 

 the surface of the water. The head of the latter rotates 

 and, according to Howard, can be turned completely 

 round with the utmost ease, so that the insect has the 

 habit of lying with its head upside down. The adults 

 (No. 1254) are strong and bloodthirsty. The female 

 Anopheles can be distinguished from the female of Culex 

 by its long palpi. When resting, the body of Anopheles 



