MALARIA EXPEDITION TO NIGERIA 89 
Manson 1 asserts to have often observed, the head of the mature larva (in fact there 
appear to be more often a pair) is in the immediate neighbourhood of this spot ; it is 
extremely probable that the larvae escape by the rupture of this thin membrane, 
which is probably already stretched by their presence, when the labellae swing out, 
and stretch the membrane still more. The escape of the larvae in this way may 
possibly be aided as the bend of the labium travels from the base towards the middle 
of that organ. 
The relation between F. nocturna and F. diurna 
The many points of resemblance between the embryos of these two worms 
suggest the question of their identity, and in favour of the view of their identity 
many facts can be brought forward. In consequence of the importance of the subject, 
and the many points of interest involved therein, we propose to treat of the arguments 
for and against in some detail ; and to arrange them under some chief headings. 
Geographical distribution. As has been already pointed out, the distribution 
of elephantiasis (caused by the presence of the adult form of F. nocturna in the 
lymphatic vessels and other sites) is extremely wide; but limiting ourselves to the 
distribution of/ 7 , nocturna, as determined by the presence of embryos in the blood, it 
corresponds in certain regions with that of F. diurna — the two occurring side by side 
throughout large tracts of country. On the other hand, however, there appear to be 
many lands where F. nocturna alone is found ; but as far as is at present known, in no 
district has it been shewn that F. diurna prevails alone. Reference must again be 
made in this connection with the conditions occurring in some of the islands of the 
Pacific, already mentioned, where elephantiasis is very prevalent, and an embryo 
occurs in the blood of many natives, which resembles very closely F. nocturna, yet 
shews none of its characteristic periodicity. 
T'he microscopical appearances of the embryos. It has already been stated that 
in West Africa we were unable to distinguish the embryos in the blood of natives 
infected with F. nocturna and F. diurna respectively, by any means whatever. They 
appeared identical in their appearance, characters, measurements and movements in 
fresh preparations and correspond in length, breadth, staining reactions, and in the 
possession of the same number of ' spots,' situated at similar points along the length 
of the worm and of the same shape and size. The sheath, a common feature of 
each, appeared identical. Moreover, the West African F. nocturna resembles very 
closely that of China and India as described by Manson. 
The numbers in peripheral blood. Here again there is a close similarity 
between the two worms. An ordinary case of either infection presents from twenty 
to sixty embryos in a drop of blood from the finger, at the time when the maximum 
number is present in peripheral blood — although in each case so many as four to five 
hundred may be present in exceptional infections. 
1. Mnnson, Tropical Diseases. London, 1901. P. 496 
M 
