FILAEIA SANGUINIS I10M1NIS IN THE MOSQUITO. 373 



the first to mention this migration ; until I had read his description of his experiments 

 on Filaria metamorphosis, I entirely overlooked this significant point. 



Most of those Mlariis that do not migrate, gradually hecome granular, their outlines 

 hecome dim and undefined, and their movements cease. I suppose they are finally 

 digested. 



If we examine carefully a Filaria that has just reached the thorax, we find that the 

 striation observed in specimens from the abdomen has disappeared ; the body is beau- 

 tifully transparent ; there is no sheath or sign of double outline ; oral movement still 

 persists, but the general body-movement has slowed down till, in some instances, the 

 animal is almost passive. The body is somewhat thicker and, it may be, shorter, and an 

 obscure undefined cloudiness can be seen in the interior (figs. 3 & 40). How far this 

 dissipation of the transverse striation, slowing of movement, and swelling may be owing 

 to endosmosis of the water that we necessarily employ in mounting the specimen, it is 

 difficult to say. I know that if the youn^ Filaria is soused in a large quantity of water, it 

 becomes so transparent that, under a low power, it is readily overlooked or even cannot 

 be seen. Sudden endosmosis, I believe, often ruptures and dissipates it. I therefore, in 

 examining the thorax of the mosquito for the Filaria at any time during the first two or 

 three days of the metamorphosis, employed a solution of sulphate of soda (sp. gr. 1050) 

 to tease up the tissues in. After application of the cover glass, the soda solution was 

 gradually diluted by placing a drop of pure water at one edge of the slide, while the 

 solution was withdrawn by a piece of filter paper placed at the opposite edge. The soda 

 solution shrivels, and renders irregular the outline of the Filaria, but by gradual dilution, 

 as described, the little animal is rendered plump and natural-looking again. I believe 

 it is the sudden immersion in water that is dangerous to the integrity of the Filaria. 

 For convenience in description, I divide the metamorphosis into six stages *. What I 

 have now related constitutes the first stage, viz. — ingestion by the mosquito, transverse 

 striation, casting of the sheath, and subsequent migration. At the conclusion of this 

 stage it is quite a common thing to find, with very little searching, 30 or 40 Filaria? in 

 the thorax, and very many more can usually be detected half concealed by careful 

 focussing? anions; the viscera and fragments of muscle. 



The first noticeable change in the Filaria after migration is a shortening and general 

 thickening of the entire body, the extreme tip of the tail being alone exempted from this 

 process. This part retains its original dimensions for a time, while the remainder of the 

 animal continues to swell. Thus the caudal appendage, characteristic of the Filaria 

 during the greater part of its stay in the mosquito, is formed. In some specimens a 

 thick hyaline-looking substance seems to cover as an integument the body of the animal 

 from the mouth downwards, stopping short, however, almost abruptly at the root of the 

 tail. The tail in all cases is evidently of the same structure as the interior and mass of 

 the body. In others, the integument I mention is not observable, the tail seemingly 



* The reader must bear in mind that this division of the metamorphosis is entirely artificial. No such thing exists 

 in nature. What I describe as stages, in reality overlap each other ; the graduations of development insensibly merge 

 one into another. 



