| dc.description.abstract | Among mammals, it is only in the order Primate that the extant members in fair
measure present graded features approximating to the stages of the evolution from the
early ancestral (prosimian) primates through to anthropoid apes and man (Huxley,
1863; Clark, 1962, 1970). The primates hence constitute a remarkably heterogeneous
and variably specialised taxon exhibiting a notable range of body size and differing
modes of life (Heglund, 1985). Classification of the primates attracts great attention
due to its relevance to the evolution of man (Charles-Dominique, 1970). The
prosimians which include the lemurs, bushbabies and tarsiers are regarded
behaviourally, anatomically and physiologically to be the most primitive living
primates (Szalay, 1968; Charles-Dominique, 1970, 1978; Bourliere, 1974) and exhibit
many unique structural and functional features which, when viewed comparatively,
illustrate the primate phylogeny (Napier & Walker, 1967). Studies of the prosimian
biology, however, only received interest in the relatively recent past (Doyle & Martin,
1974; Martin, 1978; Stevens, Edgerton, Haines & Meyer, 1981). The present studies
have illustrated that this group is in some respects functionally and structurally unique
among the primates. The basal metabolic rate (BMR), for example, has been shown
to be lower in the prosimians (Muller, 1979, 1985) than in the simian species, where
the BMR is close to, or higher than, that predicted from body mass (Bruhn, 1934;
Malinov & Wagner, 1966; Morrison & Middleton, 1967; Nakayama et al. 1971). Body
temperature in the simiae is generally 10 to 2 °C above that of most prosimian species
(Muller, 1985). Heat exposure was observed to cause great elevation of the respiratory
frequency in the greater bushbaby (Galago crassicaudatus) than in the baboon (Hiley,
1976) and, in the same study, water loss through the skin in the bushbaby was found
to be relatively very low. The response speed of the rhesus monkey was found to be
by far greater than that of the prosimians (Ehrlich, 1968a,b). Morphologically the
bushbabies have an atypically well-developed rete mirabile in the limbs for countercurrent
heat exchange and a thick woolly cover (Whittow et al. 1977).
The lesser bushbaby (Galago senegalensis), the subject of this study, is a small
member of the family Lorisidae. It is the most populous primate in Africa (Haines,
1982) and adapts well to maintenance in captivity and to the rigours of experimental
manipulation (Stevens et al. 1981). Despite these favourable features, the potential of
the bushbaby as an experimental primate model for biomedical research has not been
well exploited (Stevens et al. 1981; Haines, 1982). The main contributing factor may
be due to the paucity of published detail on the morphology of these elusive, habitually
arboreal and nocturnal animals compared to, for example, the more easily accessible
New World and Old World monkeys and the anthropoid apes which are more frequently used as animal models for human studies. In spite of the assumed closeness
between man and the other simians, it is becoming evident that the fact that two
groups of animals are systematically placed in the same higher category is by itself no
guarantee that a particular system under investigation is an appropriate model for a
human system, as is apparent from accounts by Stevens et al. (1981) and Haines
(1982). The prosimians, for example, in general have a well-developed appendix which
is absent in the monkeys and present in man. These differences have apparently arisen
from the differing extents in the evolution and adaptations that the various primate
groups have undergone (Clark, 1970). The objectives of the present study were as
follows. Firstly, to describe the morphology of the lung of the lesser bushbaby Galago
senegalensis, which has hitherto not been investigated. Secondly, to establish the
morphometric features of the structural components of the lung in an attempt to gain
an insight into its anatomical gas exchange potential. Thirdly, to compare such data
with those from other primates that have been investigated to a similar extent and then
to correlate them with the mode of life that this bushbaby leads. Fourthly, to evaluate
whether the lung of the lesser bushbaby could be, structurally, an appropriate organ
model for biomedical pulmonary studies. | en |
