7 o THOMPSON YATES LABORATORIES REPORT 
Fifth Stage. When the body has attained its maximum thickness, lengthening 
and thinning begin at the head end. The mouth inclines to purse up. The 
anterior and posterior ends may elongate simultaneously ; more generally the 
process occurs throughout the whole length of the body of the larva. When the 
mouth closes, as it does later, all or nearly all trace of viscera and all traces of cells 
vanish. About the seventh day the body assumes a fibrous and very transparent 
appearance. Before this stage there can be made out a fully moveable alimentary 
canal, pharynx and oesophagus. Slight movements commence at the neck of the 
animal and extend downwards. Manson thinks that about this stage a general 
ecdysis occurs, and the sickle shaped tail is cast off : a new skin can be seen covering 
the tail end, inside the sickle. Large cells appear at the end of the tail and form 
three or four papillae which characterise the larva at the end of this and during the 
next stage. 
The worm has now reached a length of inch in length (1*5 mm.), its 
breadth has decreased to about one-half. The anterior end tapers and is abruptly 
rounded oft ; the posterior end also tapers slightly from the anus backward and is 
covered by the papillae just mentioned. 
Sixth Stage. Movements become more active. The mouth is pursed up 
into a cone with lips firmly approximated ; minute horny papillae are present. 
The worm measures ~ by - l - n inch (V5 mm. by 0^03 mm.) 
Up to 1900, this was supposed to be the complete development of the filaria 
in the mosquito, and at this stage it was conjectured that, on the death of the 
mosquito on the surface of the water, the young filaria escaped from the insect 
and swam about until it was taken up by man in drinking water. 
In 1900 Low' in sectioning a number of filariated mosquitoes discovered a 
worm in the proboscis. He thus describes the transformation into the seventh 
stage : — ' When the filariae have reached their highest stage of development in the 
thoracic muscles, they leave that tissue and travel forward in the direction of the 
head of the mosquito and pass into the loose cellular tissue which abounds in the 
prothorax near the salivary glands. Some struggle between the thorax and abdomen 
or within the abdomen itself. They then pass into the neck, enter the lower part of the 
head and coil themselves up in the loose connective tissue immediately below the 
cephalic ganglion and salivary sack. They pass into the proboscis by making an 
independent passage through the base of the labrum and pushing forward along the 
proboscis between the labrum and hypopharynx amongst the stilettes. Here they 
are found stretched along the length of the proboscis, head foremost. Two worms 
nearly always live together in the proboscis.' 
James 2 apparently was working at this subject at about the same time, and 
writes in an article, dated September, a description of the worms as seen in Anopheles 
1. Low, British Medical Journal, 19CO, June 16 
2. James, British Medical Journal, 1900, vol. ii, Sept. I, p. 535. 
