24 
Ornithodorus savignyi 
corresponding increases in breadth are 9-1, 25-0, 40-0, 47-7, 25-8 and 23-1 per 
cent, respectively. The percentage increases in length and breadth from 
nymphal to adult stages correspond closely in both species, e.g. the percentage 
increases in length x breadth in 0. moubata, from fourth nymph to male, are 
32 x 28—-while in 0. savignyi, the increases are 36 per cent, x 26 per cent. 
Fig. 1. Ornithodorus savignyi, hypostomes in ventral aspect: ( b ) to (g) of 1st to 6th stage nymphs; 
(*) and U) of females from 4th and 6th stage nymphs; (k) and (l) of males from 3rd and 5th 
stage nymphs. (N. C. del.) 
Changes in external anatomy undergone during development. 
(a) The Hypostome. Fig. 1. 
The changes in the dentition of the hypostome during the development 
from first nymph to adult are indicated in Fig. 1, (6) to ( g ) representing the 
nymphal organs arranged in order of development, (i) and ( j) the hypostomes 
of females emerging from fourth and sixth nymphs, and (k) and (l) of males 
from third and fifth nymphs respectively. 
On comparison with the hypostomes of 0. moubata, it will be observed that 
in this species also several proximal rows and the distal row of teeth are 
equally poorly developed and their arrangement difficult to determine, that 
in the first and second nymphal stages the number and arrangement of the 
teeth are very similar, but that in the later stages the number of teeth is 
considerably less, owing to the presence of smaller numbers of rows and files. 
The changes taking place during development consist of an increasing com- 
