natural, history

I.1117.~ O.2mmFig. I. Raillietina (R.i insignis. Ventral view of young segment (semi-diagrammatic); c. s., cirrus-sac;ov., ovary; t.,t., testes; v. "., ventral excretory canals ; va., vagina; ". d., vas deferens; I'it., vitelline gland.The genital pores occur regularly on the right side and each is situated a little infront of the middle of the segment. The genital atrium is small. The cirrus-sac is moreor less pyriform throughout the strobila and measures 0.12-0.15 mm. in length and0.05-0.062 mm. in maximum width. When viewed in a whole mount, the middle regionof the cirrus-sac often appears to be slightly constricted, owing to a muscularthickening of the wall in that region. The cirrus is muscular and unarmed. The vasdeferens is much coiled and enveloped by a mass of gland-cells. It extends along theanterior border of the segment to the middle. On entt.'ring the cirrus-sac the vas deferenswidens into an internal seminal vesicle. There are 14 to 18 testes, of these 4 or 6are behind the vas deferens on the poral side of the segment, and the remaining to to12 on the aporal side.For a distance of about half the length of the cirrus-sac, the distal portion of thevagina has a muscular wall invested with gland-cells and lined with a cuticle. Fromits opening behind the cirrus-sac, the vagina extends to the female gland-complex,situated in the middle of the segment. The ovary lies in the middle line and its outlinevaries accord1ng to its development, for in the early mature segments it appears as aslightly lobed organ, but in older segments it is a bilobed structure with deep indentationsalong its margins. The vitelline gland is compact and situated immediatelybehind the ovary. The eggs are enclosed in egg-capsules, 6-10 in each capsule. Thesecapsules are somewhat oval or spherical and have a diameter varying between O. 1-0.12 mm. They are closely packed in the medullary parenchyma, between the ven tralexcretory canals. The eggs are subglobular, with an outer membrane measuring 32-37 il-. in diameter, while the onchospheres are spherical, with a diameter of 17-20 [.1-.Details obtained from the individual sets of material, together with similar informationtaken from STEUDENER'S original description, are enumerated in the followingtable:In one of the Rennell Island specimens there is a segment that possesses two genitalpores, one on either side, but only a single set of gonads (fig. 2.). So far as the writer isaware, no similar anomaly has been reported hitherto in a species of the genusRaillietina, Through this apparent anomaly, it is easy to suppose that the genusCotugnia, found primarily in Columbiform birds, might have been derived directly84