peratures after 24 to 60 days. Whereas an occasional female dies as soon as oviposition is completed, others may survive for a few days or, exceptionally, for a month. One tick deposits from 2400 to 4800 eggs.

In nature, the yellow dog-tick doubtless may produce two generations a year. Lounsbury reared three generations a year in an incubator. Taking average figures for ticks raised under favorable conditions, the cycle may be completed in 123 days, as follows:

The distribution of H. 1. leachii has been determined for South Africa by Theiler and Robinson (1953A). The most important factor in limiting this tick's spread there is increasing aridity. Twenty inches of annual rainfall, irrespective of vegetation type, appears to be the critical level there.

However, in northern Sudan, where rainfall is absent or considerably less than ten inches annually, H. 1. leachii is still fairly common on foxes.

In the Nile Valley of Egypt, where rainfall is nil to exceedingly low, the tick thrives. But, it should be stressed, the microhabitats of its larval and nymphal host, the grass rat, Arvicanthis n. niloticus, are more humid than elsewhere, situated as

they are beside irrigated, cultivated fields or in dykes. We have never found these ticks in burrows in the desert, even on the Mediterranean littoral where burrows are frequently patently damp. Foxes that pick up newly-molted adult ticks, probably from vegeta tion near grassrat burrows when they forage in cultivated areas at night, retreat to very dry desert caves and dens to rest by day. In these situations, evaporation from the host skin may be the factor that allows the parasite's survival.

A comparative study of the survival of Northeast African and South African populations under local conditions of humidity and temperature should be of considerable interest.

Theiler and Robinson (1953A) have also found that H. 1. leachii does not occur in those parts of South Africa with over sixty days of heavy frost per annum. It is generally absent from the arid Karroo except where grasses are present. Altitude does not effect the distribution of the yellow dog-tick within the limits of critical frost days noted above. Variability of incidence in various zones of South Africa is also discussed.

According to Lewis (1939A), H. leachii (probably including both subspecies HH) occurs in all districts and altitudes of Kenya but seems to prefer the shelter of dense shrub and grassy woodlands. In some areas it is more common on dogs than is R. s. sanguineus.

Theiler and Robinson (loc. cit.) state that the immature stages of H. 1. leachii may feed on dogs. Our experience in East Africa, Egypt, and Arabia indicates that nymphs are very rarely found on roaming wild carnivores such as mongooses, civets, and jackals, but that larvae and nymphs frequent rodent burrows. Onderstepoort records (Theiler, correspondence) show one hundred collections of nymphs from murid rodents, one from cattle, one from shrews, one from Felidae, one from hares, eight from elephant shrews, three from mustelids, five from springhaas, four from squirrels, three from mongooses, and one from civet. It is obvious that many factors governing the life cycle and possible variability in host preference of immature stages remain to be determined from field studies.

Roberts (1935) found larvae and nymphs in the Nairobi area common on various field rodents and in their nests. These are

the same as those listed for R. s. simus (page 743). The writer's experience in other parts of Kenya in general confirms Roberts' findings. However, Roberts observed that nests of Mastomys (= Mus) coucha near the surface of the ground rather than deeper nests are preferred by H. leachii, but I do have numerous records from deep er nests of grassrats. This factor also requires further study (See R. s. simus, page 746). It is of some interest to note that all specimens that have been reared in our laboratories from nymphs from rodent nests in Kenya, the Sudan, and Egypt have been sub species leachii.

The chalcid wasp parasite Hunterellus hookeri has been bred from nymphs in South Africa (Cooley 1929,1934). This subject is further discussed under R. s. sanguineus (page 710).

MAN:

DISEASE RELATIONS

Boutonneuse fever (Rickettsia conorii).

Experimental evidence indicates efficiency as a vector of Rocky Mountain spotted fever (Rickettsia rickettsii).

MAN AND ANIMALS: Q fever (Coxiella burnetii).

DOMESTIC DOGS: Canine babesiosis (Babesia canis).

?DOMESTIC CATS: Feline babesiosis (Nuttallia felis).

?JACKALS: Canine babesiosis (B. canis).

REMARKS

A gynandromorph of H. leachii (probably subspecies leachii) has been described and illustrated by Santos Dias (1953C). The misshapen specimen of H. leachii described and illustrated by Nuttall (1914A), and widely quoted by subsequent authors, refers to the Asiatic subspecies indica Warburton, 1910. Very slightly misshapen specimens, due to injury, of both African subspecies have been described and illustrated by Santos Dias (1955A). The measurements and increase in relative size from stage to stage have been studied by Campana Rouget (1954), apparently from data in Nuttall's Monograph.

It should be noted that some gradation appears between the two African subspecies of H. leachii and that a few specimens do not conform strictly to the criteria for one or the other form. The third subspecies, indica Warburton, 1910 of southern Asia, is more like the subspecies muhsami than like the subspecies leachii, and is distinguishable from both by minor but apparently constant and valid characters.

Dr. G. Theiler and the writer for several years have been collaborating on a morphological study of considerable series of this species from a variety of hosts and localities. The results, with complete data, will be presented in a separate report. The variety humerosoides, common on canines, informally proposed by Theiler (1943B) for the large, narrow, elongate form with extreme ventral projection of spurs, appears from this study to be an extreme body form of the somewhat variable H. 1. leachii and not a separate morphological or biological subspecies. In numerous long series of specimens from single hosts, gradations from this to less extremely narrow and elongate forms occur. There are, however, suggestions that the extreme form is a reflection of particular host factors, and application of some of the more com plex aspects of newer taxonomic concepts may eventually justify the name humerosoides.

IDENTIFICATION

Males. This long, narrow tick has tarsi II to IV gradually tapering; punctations numerous, mostly small, and discrete; palpi obtusely angled and widely triangular, widest at level of basal third, with lateral margin straight or very slightly convex but almost never concave; basally both dorsally and ventrally forming a conspicuous and usually strong spur just laterad of the point of insertion; palpal segment 3 with a retrograde spur that is long and tapering; basis capituli with lateral margins varying from almost parallel to somewhat divergent anteriorly and with cornua that are usually large and pointed; coxae always with a distinct basal spur overlapping the basal margin and with a number of long, conspicuous hairs. This combination of characters must be considered in separating males from those of other species and from the subspecies muhsami.

The scutum varies from about 2.3 mm. to 3.8 mm. long and from 1.2 mm. to 1.9 mm. wide; average specimens are about 2.6 mm. long by 1.3 mm. wide. This length_width ratio is important in comparing this subspecies with muhsami, though a few intergrade specimens, with respect to this feature, do occur. The punctations, always numerous and mostly comparatively small, are usually discrete; they cover the entire dorsum including lateral areas and festoons but frequently are reduced in the narrow, elongate area correspond ing to the posterior median groove of rhipicephalids. The long, narrow lateral groove encloses the first one or two pairs of festoons; the closely approximated, arched cervical grooves usually extend to the anterior level of the lateral grooves. The scutal surface is more or less arched.

The palpi are notable for their wide, obtusely angled form. The lateral margin, either straight or very slightly convex in outline, distinguishes this subspecies from muhsami, but, rarely, a similar form occurs on ticks with the short, broad scutal type of muhsami. The recurved basal margin is typically broken both dorsally and ventrally by a strong spur just laterad of the point of insertion; while this spur is usually accentuated in large, narrow, elongate specimens it is surprisingly reduced in some in dividuals of this type. The ventral retrograde spur of palpal segment 3 notably is consistently strong, overlapping the base of segment 3, and narrow and tapering. Segment 3 is about half as long as segment 2. The basis capituli, typically, is elongate with strong, tapered cornua and with lateral margins slightly divergent anteriorly, but the length width ratio and size and shape of the cornua is surprisingly variable, even in specimens in which the general appearance would otherwise lead one to expect that these features would be typical, and the degree of divergence of the lateral margins is also somewhat variable. The hypostome has 4/4 or 5/5 dentition.

The coxae are notable for the basal spur that overlaps the basal margin and for the presence of twelve to twenty long hairs on each (hairs may be broken or rubbed off in old or carelessly collected or preserved material). The size and position of these spurs always approximate those illustrated herein and are important in distinguishing this species from some others. In newly molted or fresh specimens, the numerous long hairs are a very characteristic feature of this species. The elongate tarsi taper gradually