FILAKIA SANGUINIS HOMINIS IN THE MOSQUITO. 377 



(figs. 2G, 29, 30). When the mouth closes, as it does presently, all or nearly all t ace of 

 viscera and all trace of cells vanish. The body assumes a fibrous and very transparent 

 look, and little structure can be made out. 



The movements just alluded to begin in the neck of the Fllaria. At first they are of a 

 gentle to-and-fro swaying character ; but gradually, as the whole body becomes attenuated, 

 they extend backwards pari passu with the attenuation, and until the entire length of the 

 animal becomes more or less animated. These movements do not last longer than a few 

 minutes, at this stage, after immersion in water, differing in this respect very much from 

 what happens at the next stage. 



The fate of the sickle-shaped caudal appendage, which up to this time has been so 

 characteristic of the growing Filaria, is a little doubtful. It may be that the extreme 

 end of the now truncated body gradually forces its way into the remains of the tail, from 

 which it had before retreated, stretching it so as to have it as a closely fitting integument. 

 More probably the sickle is cast off in a general ecdysis, which about this stage, I believe, 

 occurs. Fig. 46 tends to show that this is probably what really happens ; a new skin is 

 shown covering the papillated tail, inside of and quite distinct from that constituting 

 the " sickle." In the example from which this sketch was made, on tracing the skin, 

 continuous with the " sickle," forwards, a point, about abreast of the anus, was reached 

 where it seemed to be peeling off or breaking down. 



About this time at the very extremity of the truncated tail, two or three cells become 

 prominent, their nuclei enlarge, and the surrounding protoplasm is increased in bulk. 

 These cells after a time protrude from the general surface, and gradually become 

 converted into the circle of three or four papilla? which characterizes the Filaria at the 

 end of this, and during the last stage of metamorphosis (figs. 30, 31, 43, 46, 32, 33). I 

 am not sure if one or two of these papilla; be not the remains of the stump of the original 

 tail ; nor aoi I quite sure of their number, as it is usually impossible to obtain a view in 

 which all can be seen at once. After a time the papillae spread out like the petals of a 

 flower, extending considerably beyond the margin of the circumference of the body, so 

 that in time they become the broadest part of the animal. 



The purpose of these caudal papillae is difficult to divine. Possibly they are of use in 

 aiding the animal in its future journey through a human host. One can understand 

 how by opening out on any retrograde movement they will prevent this, give a firm foot- 

 hold, so to speak, to the boring Filaria, and favour forward movement. They are not 

 oral, as I at one time supposed. 



Together, the papillae, the anus, and alimentary line are very deceptive, and give the 

 idea that this part is really the head of the animal, the papilla? apparently surrounding a 

 mouth with organs of generation opening in close proximity, as is so commonly the case 

 in the Filarial. But I have satisfied myself that in these features we have really to do 

 with the tail of the animal, not the head. 



During the progress of these changes the Filaria has gradually stretched from perhaps 

 the fortieth to the sixteenth of an inch in length ; at the same time its breadth has 

 decreased one half. The anterior end tapers gradually and is then abruptly rounded off, 

 hardly any structure being visible about it. The posterior end also tapers slightly from 



55* 



