:M4 
Ornithodorus moubata 
The round plate of the first nymph becomes comma-shaped in the second 
nymphal stage, owing to the formation of an anterior horn. In the next stage, 
the horn is prolonged ventrally and the plate extends posteriorly. In the 
fourth and fifth stages the plate develops on the same lines, in the latter case 
being almost semicircular. Tn the last two stages, the two ends of the plate 
tend to close in on one another, the anterior end being directed posteriorly 
and the posterior end ventrally. 
The plate of the adult resembles that of the equivalent nymphal stage, as 
a comparison of ( h ) with ( d ) and ( j ) with ( e ) in Fig. 4 indicates. The spiracles 
of adults from fourth (3) and fifth (?) nymphal stages are intermediate in 
structure between those illustrated. Variations in the shape of the plate for 
any one stage are not very pronounced. 
Fig. 4. Ornithodorus moubata, outlines of cribriform plates of spiracles: (a) to (#) of 1st to 7th 
stage nymphs; ( h ) and (i) of males from 3rd and 5th stage nymphs; (j) and (k) of females 
from 4th and 6th stage nymphs. Top = anterior, right = dorsum. (N. C. del.) 
It is possible therefore, from a consideration of the structure of hypo- 
stome, spiracle and fourth tarsus, to determine approximately the stage of 
development which a tick of this species has attained. The effect of mal¬ 
nutrition in inducing variation is very pronounced in other genera of ticks, 
as shown by Nuttall (1913) and Cunliffe (1913) and has not been thoroughly 
studied in this species. The hypostomes show some variation between indi¬ 
viduals of the same stage, with regard to the total number and arrangement 
of the teeth and further study will probably show that the dentition of a 
small and poorly developed individual will tend to approach that of a normal 
tick of a preceding stage. Very considerable variation occurs in the tarsal 
humps of small and normal nymphs of the same stage (vide Fig. 3), but as 
far as was ascertained, the spiracular variation was not very pronounced. 
