NOTES ON A VIVIPAROUS DISTOME. 



By Edwin Linton, 



Of Washington and Jefferson College, Washington, Pennsylvania. 



During the summer of 1912, while engaged m work for the United 

 States Bureau of Fisheries, in attempting to get some phases of the 

 life history of certain trematode parasites of fishes, I examined a 

 number of birds. Of the many interesting forms which were thus 

 secured, one is, in a measure, unique in that not only are ciliated 

 larvae (miracidia) found in the uterus, but each miracidium was found 

 to contain a well developed redia. 



PARORCHIS AVITUS, new species. 

 Plate 43. 



Miracidia in the ova of distomes have been recorded and larvae 

 containing redise have been noted in certain of the Monostomidse, 

 but so far as I am acquainted with the literature of the subject, this 

 is the first record of such occurrence in a distome. 



The distomes here described were obtained from the cloaca of a 

 herring gull {Larus argentatus) at Woods Hole, Massachusetts, 

 July 22, 1912. Ten specimens were found in one gull. Search was 

 made for this interesting form by me during the remainder of the 

 season of 1912 and again in the summer of 1913, also by Mr. Vinal 

 N. Edwards in the interval between the two summers, but no more 

 of these worms were found. In life they were leaf-like with outlines 

 varying with the state of contraction, very different shapes being 

 assumed by the same worm at short intervals (figs. 1 and 2). The 

 color in general was white with a faint reddish-brown area toward 

 the posterior end. This reddish-brown area is the region occupied 

 by the posterior folds of the uterus in which the eggs are sufficiently 

 colored to impart a color to the body at that point. The space in 

 front of the brown ova, as far forward as the ventral sucker, is filled 

 with large, thin-walled ova, each with a distinct spot of black pigment 

 showing through the transparent shell of the ovum and the body 

 wall. This is a conspicuous feature of the living worms when they 



Proceedings U. S. National Museum, Vol. 46— No. 2040. 



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