M2 GEORGE H. r. NUTTALL. 



2. Oviposition. 



The replete and fecundated female seeks shelter on the ground and after a variable 

 period of time, depending on temperature, proceeds to lay eggs. If disturbed or 

 roughly handled whilst ovipositing the female may cease to lay or she may die. 

 A female may lay a few hundred up to thousands of eggs, depending upon the species. 

 Amblyomma hehraeum may lay up to 18,500 eggs, Rhipicephalus sanguineus 4,000, 

 R. appendiculatus 5,800, Hae?naphysalis leachi 4,800, Hyalomma aegyptium 15,500. 

 The process of oviposition is remarkably interesting to observe ; illustrated descrip- 

 tions of the process will be found in our work, Ticks (Parts II and III). 



3. Development. 



The eggs, when first laid, are brownish and transparent. To undergo development 

 they require a suitable degree of temperature and moisture. After some days the 

 eggs appear clouded and a white spot (due to the Malpighian glands developing and 

 accumulating excrement) appears on one side of the egg. Some days later the shell 

 splits and the small six-legged larva emerges. The larvae soon darken, their chitinous 

 exoskeleton hardens, and they scatter in search of a host. The larva of Ixodid ticks 

 frequently accumulate in clusters of several hundreds or thousands upon the ends of 

 blades of grass or herbage, and, coming to rest, wait for a passing host. If fortune 

 favours them, they promptly cling to the host by means of their sharply clawed feet, 

 which are likewise provided with pulvilli. Seeking a suitable spot on the skin of the 

 host they insert their mouth- parts and proceed to feed. They usually become engorged 

 in three to five days and then drop from the host. 



The replete larva remains torpid until it casts its skin and the tick emerges as an 

 eight-legged nymph, which again mounts the herbage and waits for its host. If a 

 host is found, the nymph behaves as did the larva. The nymphs give rise to adults. 

 These in turn wait for a host and attack it in the same manner as do the other stages. 



The length of time the tick remains upon the host varies somewhat according to 

 the species. Examples of different periods of parasitism will be found under the 

 special biological notes which foRow. If the ticks do not tap a good blood supply 

 they may remain for a longer time upon the host. Moreover, if the host is a cold- 

 blooded animal, the period of parasitism may be greatly prolonged. The males 

 frequently remain upon a host for weeks after the females ha\e dropped off, this 

 explains why males may at times be present in larger numbers upon an animal. 



Metamorphosis is markedly influenced by temperature, being accelerated by warmth 

 and greatly retarded or completely checked by cold. 



The relation of certain ticks to disease is referred to briefly under the species whose 

 biology is described in the text which follows. 



Special Biology of Congo Ticks and their Relation to Disease.* 



Ornithodorus moubata occurs in native huts and resting places, hiding in the dust 

 or thatch. It feeds chiefly at night and imbibes blood rapidly like the bed-bug. 

 The fertilized female feeds repeatedly and lays a variable number of eggs after each 



* The observations here recorded were carried out by me in Cambridge. — G. H. F. N. 



