Migration and development of Trichobilharzia ocellata in ducks was studied by examining tissues and perfusate from birds which had been exposed to cercariae 5 min to 370 days earlier. Cercariae penetrated rapidly and were carried to viscera within 24 h. In the lungs, schistosomula left the vascular system to occupy air spaces, later to reenter veins in bronchial tissue. In the liver, worms were predominantly in sinusoids on days 1–6, in veins on days 7–9, and absent on days 10 and 11. Small numbers returned to the liver, which was the only organ harboring worms between days 89 and 370. Most worms found between days 10 and 21 were in the veins and tissues of the gut but none were there after day 21. Oviposition began on day 9, and peak numbers of eggs were found in the gut wall on days 14–16. Growth and development of T. ocellata were rapid. Caecal union was complete by day 2, organogeny by day 4, gametogeny by day 6, and sexual maturity and adult size by day 7. Morphological description of developing forms and of adults are given, the latter based upon examination of forty 9-day-old specimens of each sex.

No abstract

Migration, development, and condition ofTrichobilharzia ocel!ata (Trematoda: Schistosomatidae) in homologous challenge infections. Can. J. Zool. 53: 1803-181 1. Ducks previously infected with Trichohilhar& rrceZ1ara were challenged by exposum to conspecific cercariae. Comparisons were made among worms recowred from teased or squashed tissue or locared in sections, after first, second, or multiple challenges. Contrasting with 24 h clearance in initial infections. schisrosomuIa were retained in the skins of challenged birds, mainly in the stratum corneum, for up to 7 days. Pdrasites reached the lungs as early as day 1 in first and second c hallenges but more than 50% bf these were adhering to brc~nchial wall? in mucoid material. After thlrd challenpe. wormswere seen in the l u n a~n davs 3-7 b u~ 35-H3%of these were coated with lymphoid ce~s.-Schistosomula were found in ;fie liver5 of 16/19. 411 5 , and 2120 birds examined aner firql, second, and multiple challenges respectively, most being in sinusoids surrounded by lymphocytes. No worm\ assignxble to challenge infecl~ons were found in the hosts' inlestinal veins. Parasites which survived 7 days in challenge infections reached lengths of about 300 pm. shout I k 1 5 % of the normal value. Those from 16\19 birds retained cercarial features such as tegumental spines, eyespots, and head organs.

Acute overdistension of the stomach, quite apart from excessive ingestion of foods or drinks, is a well-recognised complication both of acute diseases such as typhoid fever, scarlet fever, lobar pneumonia, and pericarditis, and of certain sub-acute or

Evaluation of reproductive success by Trichobilharzia ocellata was based upon numbers of miracidia hatching in sidearm flasks. Hatchable eggs appeared in feces 13–14 days after the duck's foot was exposed to cercariae, rose to peak numbers by about day 19, then declined to zero, usually by day 45. Patent infections also resulted from implantations of 10–100 unsexed adults and in some but not all birds exposed to 10–25 cercariae on 51 consecutive days. Most birds challenged by massed cercariae failed to support egg-laying second populations regardless of whether the initial infection followed cercarial invasion or implantation of adults.