Studies on the Helminth Fauna of Alaska. X. Morphological Variation in Hymenolepis horrida (Von Linstow, 1901) (Cestoda: Hymenolepididae)

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Abstract
Data derived from a critical study of morphological variation in H. horrida obtained from a series of microtine rodent hosts of wide geographical distr. is presented. Specimens of H. horrida were studied individually irrespective of host and geographical locality from which they were collected. Avg. measurements and ranges were detd. and comparisons made of such morphological characters as: scolex size and shape; sucker diam.; testis size, shape and arrangement; cirrus sac size, diam. of cirrus, and cirrus spine size; extent and shape of ovary; vitelline gland shape; and egg size. On the basis of frequency of occurrence, measurements of organ variation in H. horrida indicates that the diversity found in organ shapes is significant. The more extreme differences, in each case, appear to be interconnected by a series of intergrading forms, suggesting a certain regularity in the pattern of variation. With the possible exception of cirrus diam. and cirrus spine size, none of the characters shows mutual or reciprocal correspondence of relationship in their variability. Although variation in testis shape ovary shape, vitelline gland shape, and cirrus spine size may be concomitant, variation in one character appears to be completely independent of variation in any other character. Egg development in H. horrida is discussed and modified diagnosis of H. horrida. based on this consideration of morphological variation, is given.
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