252 TIMOTHY RICHARDS LEWIS. 



Manson as " sausage-shaped ^'), almost perfectly still (fig. 10)^ 

 with a faint indication of a mouth ; and^ in some of them, a 

 faint line may be detected suggestive of a commencing intestinal 

 canal ; the escape of a few granules on slight pressure towards 

 the other, usually thicker, end, suggests the existence of an anal 

 aperture. The chief difficulty which I have experienced in 

 following these changes is to account for the transition of form 

 at figure 7 to that represented in figure 10. They are all, up to 

 this figure, sketched as magnified by 300. 



The larval forms at fig. 10 now rapidly increase in size, anci 

 gradually acquire a more elongated outline, and between the 

 fourth and fifth day they may be found presenting the form 

 shown at fig. 11. The last figure, it will be noticed, is magnified 

 100 diameters only, and the length of the larvae, therefore, is 

 almost three times that of those delineated at fig. 10. They also 

 manifest greater activity. 



The highest stage of development which has come under my 

 notice is that figured at 13 as seen magnified 100 diameters. 

 The anterior and posterior portions of a similar one, magnified 

 300 diameters, are delineated at fig. 13. This measured -j^-j of 

 an inch in length, and its width towards the middle was -g-^-^- ; 

 near the anterior and posterior ends they nieasured ^-u" across. 

 The dimensions of another specimen which I measured were ^" 

 in length by — o-uir" in width at the broadest part. Dr. Manson 

 mentions that he has on four occasions observed larger speci- 

 mens than these. 



Notwithstanding their activity and apparently robust condition, 

 they nevertheless are extremely fragile, very slight pressure of 

 the cover-glass being sufficient to crush them. When examined 

 in the unbroken condition it is only with difiiculty that the ali- 

 mentary canal can be distinguised beyond the junction of the 

 oesophagus with the intestine, but when carefully ruptured (as in 

 fig. 12) the tube may be distinguished. I have not been able 

 to distinguish any other differentiated viscus in any of the speci- 

 mens which have come under my observation, and, certainly, 

 nothing suggestive of differentiation of sex. 



By the time that the larval filarise have attained to this degree 

 of development, the mosquito will possibly have already deposited 

 its ova and its own cycle will have been nearly completed. With 

 the intention of following out the development still further, I 

 have frequently kept insects until this stage was reached before 

 examination, but all the attempts have proved fruitless, notwith- 

 standing that the mosquito has been seen to go through its 

 ordinary course of depositing its ova on the surface of water, and 

 then perishing itself. Either no filarise were found in its body, 

 or if present they were dead, and careful examination of the 



