BY T. HARVEY JOHNSTON, M.A., D.SC. 217 



are frequently present on weakly young animals ; that the 

 situation of the nodules is under those parts of the skin 

 which most frequently harbour lice ; and that the south- 

 ward advance is slow. They, moreover, found a living 

 embryo in a louse* which had been fed on an inoculated 

 part of a heifer. It seems to me that the mosquito, the 

 true lice, and the " cattle-fly " — a species of Musca, fre- 

 quently found associated with Queensland cattle — are the 

 most likely agents. The great objection, however, lies in the 

 iact that, as yet, the embryos have not been detected in 

 the blood-stream, and have not been found beyond the 

 nodule.f Even after centrifugalising large quantities of 

 blood, Gilruth and Sweet were unable to detect their 

 presence. In regard to the allied parasite, 0. gutturosa, 

 from the Algerian cattle, Emery (in Neumann, 1910, p. 271) 

 mentioned that he had not been able to find embryos in 

 the blood. 



The life history is not yet known in any species of 

 Onchocerca. Brumpt (1904, quoted by Fiilleborn, 1908, p. 15), 

 Fulleborn (1908, p. 15), and Rodenwaldt (F. and R., 1908, 

 p. 83), found embryos of 0. volvulus in the peripheral parts 

 of the tumours from human beings, and the first named 

 author believed that a Tabanus, Glossina or Simulium 

 might act as a transmitter. None of these authors, nor 

 Parsons (p. 366), detected embryos in the blood, but the 

 latter worker states that the distiibution of 0. volvulus 

 " suggests the existence of a riverine intermediary," and 

 believes it highly probable that embryos must pass some- 

 time in the general circulation (p. 367), the transmitting 



* Dr. Cleland and myself have examined a large number of lice 

 (Haematopiniis vituli, L.) and Mallophaga {TricJiodectes hovis, L., sjn. Tr. 

 scalaris, Nitzsch), taken in New Soath Wales from a young calf infected 

 with nodules, but without result. Of course the Trichodect is not likely to 

 be a normal carrier on account of its food being epidermal structures and 

 Jiot blood. Sometimes blood is found in the crop, but this is not usual, 

 the blood entering from wounds along with the ordinary food. 



f Park in a footnote to a paper (Barnard and Park, 1894, p. 645) refers 

 to finding " young Spiroptera in some of the blood vessels." Though Dr. 

 •Clelind and myself, as well as Professor Gilruth and Dr. Sweet, have 

 worked through series of sections, we have not been able to find embryos 

 in the blood. Park's statement stands quite unconfirmed up to the present 

 as regards Australian cattle. It may be mentioned, however, that De Does 

 .^1904) found the embryos in the blood of Javanese cattle, and thought 

 ihat blood-sucking insects were the most likely transmitting agents. 



