MALARIA EXPEDITION TO NIGERIA 87 
shows a complete alimentary canal and reproductive apparatus (although immature) 
similar in site and arrangement to those of the adult worm as found in man, it seems 
certain the next stage in the life history is carried out in the definitive host — man. 
It has been suggested, that as mosquitoes can be sometimes observed feeding on such 
as bananas, that the filariae are capable of exercising a selective instinct for their 
escape at the time of puncture : and it has been further suggested that possibly the 
filariae may escape into banana and other food stuffs, and either undergo a further 
period of their life history in the external world, or without further change be 
introduced into the alimentary tract of man. All these suggestions appear to us 
exceedingly improbable. We have previously shewn, 1 and there is a considerable 
amount of other evidence to support the facts, that a fertilized female mosquito of 
the blood-sucking species of West Africa requires blood regularly for the maturation 
of her ova, and that she will have blood and nothing else : and since those species 
capable of carrying human filaria frequent the neighbourhood of human habitations, 
they will for the whole period of their existence feed on blood, and generally on 
human blood — so that the possibilities of the escape of the filariae into banana and 
other substances are extremely vague, and further, it becomes quite unnecessary to 
suppose the possession by the larvae of any selective instinct. The occurrence of the 
larvae in such a position leads one to presume that they leave it before, during or 
after the act of suction of the blood; and Grassi and Noe 2 claim to have infected a 
dog by the bites of Anopheles infected with F. immitis, although, since a single broken 
immature worm only was discovered, post-mortem, some sixteen days after the 
mosquitoes had been allowed to bite them, this experiment urgently requires confir- 
mation. These investigators, however, assert that in specimens of the numbers of 
mosquitoes which were allowed to bite the dog, before the experiment, larvae were 
found in their labia, while after the experiment, many labia were dissected and found 
empty. 
Grassi and Noe in their article go on further and describe how the larvae 
leave the labium. After drawing attention to the bending of the labium, as the 
stylets gradually penetrate the skin, so that the angle formed advances from near the 
base to the middle of the labium until the labium appears almost completely doubled, 
they 'add the two halves of the olive and the little tongue resting against the skin of 
the animal, which is punctured, embrace the six pieces penetrating the skin. It is 
certainly through the bending of the labium, stuffed with filariae, that is brought 
about the rupture of the integuments of the labium along the dorsal groove, and 
through the rupture thus produced come out the filariae to penetrate the body of 
their definitive host. It is difficult, as everyone will understand, to enter into 
further particulars. In some cases we believe that we positively found the rupture in 
the middle of the length of the labium in correspondence with the loop. It seems to 
L. Report of Malaria Expedition to Nigeria, 1 90 1. Part I, chap. iv. 
2. Grassi and Noe, British Medical Journal, 1900. Vol. ii, p. 1306. 
