MALARIA EXPEDITION TO NIGERIA 69 
The only striking feature which this table presents is the smallness of the 
number of F. perstans embryos ; the greatest number we ever observed, was thirteen 
in three specimens under three-quarter inch square cover glasses ; that is, 
approximately 2 to 3 c.mm. of blood. 
The intermediary host of Filaria nocturna : its development. 
The phenomenon of the periodicity of F. nocturna led Manson to induce the 
further development of the parasite in a blood-sucking insect of nocturnal habits. In 
1878 Manson demonstrated developmental changes in the embryos after ingestion 
by the mosquito, since when the whole of the life history in the intermediary host 
has been observed by Bancroft, James, Sonsino, Low and ourselves in Culex pipiens, 
C. ciliaris, C. fatigans, Anopheles costalis, Anopheles rossii, Bancroft has shewn that 
C. notoscriptus (Skuse), C. amuli rostrls (Skuse), C. hispidosus (Skuse) C. vigi/ax 
(Skuse), C . nigrothorax (Macquart), C.procax (Skuse) and Anopheles musivus (Skuse) 
do not serve as intermediary hosts. 
Manson 1 gives the details of the various stages of the metamorphosis of F. 
nocturna embryos in C. pipiens. 
First Stage. Transverse striation becomes well marked as if from a general 
longitudinally shrinking of the embryo ; oral pouting vigorous. In about one hour 
the embryo casts its sheath ; and then shows active locomotive movements. In 
from twelve to eighteen hours many have bored through the stomach wall of the 
mosquito and have reached the muscles of the thorax. Some die in the stomach. 
In the thorax, the striation disappears and movement ceases : the body becomes 
thicker and an illdefined cloudiness appears in the interior. 
Second Stage. The body thickens, and there is a faint indication of a mouth ; 
this stage requires two to three days for completion. 
Third Stage. The anus appears, and cells are seen in the body ; the mouth 
becomes open, and gradually four large fleshy lips are fashioned. The anus appears 
in front of the tail as a break or hole in the cuticle, from which granular matter 
exudes. The line of the cells, which are now visible in the previously apparently 
homogenous body, does not terminate at the anus but in advance of this, in some 
large prominent cells. The cells later become differentiated into an alimentary layer, 
and a tegumentary layer with a cavity between. The larva now measures 8 ^ o to i inch 
long (0*25 to o*3 mm.) and ~ to ~ o inch broad (0*048 to 0*45 mm.) There is 
considerable diversity in size and shape. The mouth is wide open ; the tail is large 
and sickle shaped, and the cells of the body usually dip into it. The alimentary canal 
runs from mouth to anus. Motion is entirely suspended. 
Fourth Stage. Growth is rapid: length i to i inch (0*35 to o - 5 mm.) The 
body retracts from the tail, which becomes a mere integumental appendage. 
I. Manson, Transactions of the Linnean Soc, 1884. P. 367 
