BY T. HARVEY JOHNSTON, M.A., D.SC. 215 



In the peri-anal group, the first pair are usually slightly 

 more prominent and somewhat separated from the remaining 

 three pair, which are really ad- anal or post-anal in position, 

 the first pair being distinctly pre-anal. Gilruth and Sweet 

 (p. 15) have noted a certain amount of variation in the 

 arrangement. The alae are not very prominent. The 

 tail end has a spiral twist, similar to that recorded as 

 occurring in 0. volvnlus. (Parsons, 1C09, p. 303.) 



The embryos measures from -22 to '35 mm. in length 

 by '003 mm. in width, the anterior end being obtusely 

 rounded or nearly straight, and the posterior extremity 

 tapering. Gilruth and Sweet have estimated that there 

 may at one time be as many as two million embryos and 

 fertilised eggs in one female. 



The internal anatomy of the parasite does not call 

 for attention in this paper. (Cleland and Johnston ; Leiper ; 

 De Does ; Gilruth and Sweet.) 



Transmission : — From the economic point of view, 

 the most important feature is the means of transmission. 

 If this be known, then one may hope to be able to formulate 

 measures to limit the degree of infection, by reducing the 

 numbers of the transmitting agents, as is now being done 

 in the case of mosquito destruction in order to lessen 

 malarial and other mosquito-borne infections. Direct 

 transmission of a filarial worm is quite unlikely. We 

 (1910, c, p. S8), as well as Gilruth and Sweet (1911, p. 26), 

 failed to inoculate calves by injecting living embryos 

 subcutaneously. An intermediate host appears to be 

 necessary. In some few cases it is known to' be a crustacean 

 inhabitating fresh water, but more frequently it is a blood- 

 sucking insect, usually a mosquito. The latter method 

 of transmission presupposes the presence of filarial 

 embryos in the blood of the final or definitive host. 

 But, as yet, these have not been found in the general 

 circulation of cattle affected with Onchocerca, nor in 

 horses harbouring 0. reticulata, nor in men infested with 

 0. volvulus. In the case of man, filarial embryos belonging 

 to other Filariidae may be met with in the blood, but in 

 cases of an infection by 0. volvulus alone, such larval forms 

 have not yet been detected. We have given a summary 

 of our results (1910, c, p. 97), which were all negative,, 

 embryos being found in the peripheral parts of the tumours, 



