224 THE ARACHNOIDS. 



fourth pairs of legs in the female have bristles, but in the male, the 

 fourth pair has suckers. The tunnels made by the female have the 

 egg-bearing female at the blind end; scattered all along are faeces, eggs, 

 larvae; the eggs being next the mother and the more mature young at 

 the entrance to the gallery. A diagnosis can be made from the finding 

 of either eggs or larvae. The eggs are 140/4 long and hatch out in 4 to 

 5 days. A female becomes mature in about 3 weeks. Different 

 animals have different species of itch mites. 



Demodicidae (Hair follicle mites). 



Demodex folliculorum This is a vermiform acarine about 400/4 

 long; the eggs are about 75/4 long; they chiefly live in the sebaceous 

 glands of nose and forehead. 



Ixodidae. 



This family of the Arachnoidea is one of great medical interest and 

 of growing importance. While only proven the intermediary hosts in 

 the case of the organism of African tick fever and the as yet undis- 

 covered cause of spotted fever of the Rocky Mountains, there is con- 

 siderable speculation as to the possibility of blackwater fever being due 

 to a Babesia (piroplasma). Piroplasmata of animals seem to be 

 invariably transmitted by ticks. 



Very important diseases due to these small pear-shaped organisms 

 within red cells are known for various animals, the best known being 

 that of cattle in Texas and known as Texas fever. Other diseases are 

 Rhodesian fever (cattle), heart water (sheep) and malignant jaundice 

 of dogs. In these diseases there are pathological features which 

 resemble blackwater fever of man. It is of interest to note that it was 

 with the transmission of Texas fever through an intermediate host 

 (the tick) that Smith and Kilborne (1889-1893) established the zoologi- 

 cal principle of transmission of disease through arthropod interme- 

 diary hosts. This led up to the work on malaria, yellow fever, etc. 

 Ticks differ from insects in having 4 pairs of legs, only 2 pairs of 

 mouth parts and no antennae. They differ from other acarines in 

 having a median probe-shaped puncturing organ, the hypostome, 

 which is beset with numerous teeth projecting backward. The head, 



