In each month for one year 30 perch. Perca fluriutilis L., 1758. were examined for infection with Acanthocephalus lucii (Müller. 1776): 7·78°, of the population was infected with a mean intensity of 2·61 worms/infected fish. No seasonality of occurrcncc of maturation was observed owing to limited data. In older fish the incidence and intensity of infection was greater than in younger specimens. The parasite was significantly over-dispersed within the perch population, k = 00395...P(x2 = 9·07)>0·05. All specimens of A. lucii were found in the third quarter of the intestine from the pyloric caeca to the rectum. Evidence is presented in favour of mutual exclusion between A. lucii and the cestode Proteocephalus percae (Müller, 1780) and the nematode, Camallanus lacustris (Zoega, 1776).

A substantial resistance to a heterologous challenge with Fasciola hepatica was demonstrated in calves harbouring primary patent Schistosoma bovis infections of an age of 10 weeks at challenge, the mean worm burden being reduced by 29·9% (p < 0025) in calves primarily infected with S. bovis as compared with that of the challenge control group. The heterologous resistance was also evidenced by less pronounced liver tissue damage and lower serum gammaglutamyl-transpeptidase values in the S. boms-infected animals compared with the challenge control group.

Remarkable hypertrophic changes were observed in the adrenal and thyroid glands of male mice after 7 to 16 days of infection with the filariform larvae of Ancylostoma caninum, but not in females. The adrenal gland revealed enormous enlargement of cells in the zonae glomerulosa, fasciculata and medulla, and also the formation of big vacuoles in the glomerular zone, whereas the thyroid gland showed distinctly hypcrtrophicd follicular epithelium with marked acolloidal condition and follicular mass formation. These changes in the cellular diameter were highly significant (P>0·001 to <0·005). The possible reasons for hyperactivity of these glands are discussed.

The karyotypes of two hermaphroditic trematodes, Megalodiscus temperatus and Philophthalmus gralli, were described and compared as to chromosomal morphology and constitutive heterochromatin constitution. The haploid number of chromosomes for both species is 10 and both karyotypes are composed mainly of acrocentric chromosomes. Constant heteromorphism of the No. 10 chromosomes was found in M. temperatus. The heteromorphic chromosomes differ is size and heterochromatin constitution. The possible mechanisms of chromosomal dimorphism in M. temperatus and its significance in the evolution of sexchromosome differentiation in trematodes are discussed.