210 



FILARIA BANCROFT! CH. 



stomach and eventually comes to rest in the thoracic muscles 

 of the mosquito. This process is usually complete in about 

 12 to 1 8 hours, but some of the worms die in the stomach. 

 In the thorax all movement ceases, the striation disappears 

 and various changes take place in the interior of the filaria. 



Second Stage. This generally occupies about two to three 

 days, during which the body thickens, and a mouth begins to 

 appear. The posterior V-spot appears as a large vacuole and 

 the anterior V-spot becomes very distinct. 



Third Stage. The mouth becomes open and four large fleshy 

 lips are formed. The posterior V-spot enlarges and definitely 

 becomes the anus, appearing in front of the tail as a break in 

 the cuticle, from which granular matter exudes. A row of 

 cells appears in the previously apparently homogeneous body 

 and terminates in front of the anus in some large cells. This 

 row of cells later gives rise to the alimentary canal and a 

 tegumentary layer with a cavity between. The larva is now 

 0-03-0-3 mm. in length by o-029-o-05 mm. in diameter. 

 At this stage the tail becomes large and sickle-shaped and the 

 cells of the body usually dip into it. The alimentary canal 

 extends from the mouth to the anus. Motion is entirely sus- 

 pended. 



Fourth Stage. Rapid growth takes place and the body 

 retracts from the tail, which becomes a mere appendage. 

 The length of the worm varies from 0"35-O"5 mm. 



Fifth Stage. When the body has attained its maximum 

 thickness the anterior end commences to elongate and become 

 thinner, and the mouth begins to close. The anterior and 

 posterior ends may elongate simultaneously, but more often this 

 process occurs along the whole length of the larva. The mouth 

 eventually closes and all, or nearly all, traces of the viscera 

 disappear. About the seventh day of development the body 

 of the worm assumes a fibrous and very transparent appearance, 

 but before this stage is reached a well developed alimentary 

 canal with pharynx and cesophagus may be distinguished. 

 Slight movements now commence at the neck of the animal 

 and extend downwards, and about this stage a general ecdysis 

 takes place and the sickle-shaped tail is cast off, a new skin 



