Fig. 193.—Diagram of genitalia of a Cestode. g.p., genital pore; ♀ ♂, male and female ducts opening into genital sinus; c.s., cirrus sac; v.d., coiled vas deferens (“outer seminal vesicle”); vag., vagina; sem. rec., seminal receptacle; sp. d., spermatic duct; C.c., fertilization canal; vit. d., vitelline duct; sh. g., shell gland; ut. c., uterine canal; ut., uterus; Ov., ovary; p, pumping organ. Cf. figs. 191 and [233]. (Stephens.)
The vagina, like the vas deferens, usually runs inwardly and posteriorly, where it forms a spindle-shaped dilatation (receptaculum seminis); its continuation, the spermatic duct, unites with the oviduct, the common duct of the ovaries (fig. 191). The ovaries, usually two in number, are compound tubular glands in the posterior half of the proglottis, which extend into the medullary layer, but ventral to the median plane.
At the origin of the oviduct there is frequently a dilatation provided with circular muscles (suction apparatus), which receives the ovarian cells and propels them forward. After the oviduct has received the spermatic duct the canal proceeds as the fertilization canal, and after a very short course receives the vitelline duct or ducts, and then the numerous ducts of the shell glands (oötype). [Although the nomenclature of these parts varies, we may consider the oviduct as extending from the ovary to the shell gland and as receiving the spermatic duct and then the vitelline duct and the ducts of the shell gland. The short piece into which the shell gland ducts open corresponds to the oötype in the flukes, but in the tapeworms this portion of the canal is seldom dilated. From this point the oviduct is continued as a shorter or longer tube, the uterine canal or true oviduct opening into the uterus proper.—J. W. W. S.] The vitellarium may be single, but often exhibits its primitive duplication more or less distinctly, in which case it is situated at the posterior border of the segments in the medullary layer (fig. 191). The original position of the double organ is, moreover, the same as in the Trematodes, i.e., at the sides of the proglottids, and thence eventually extending more or less on both surfaces (figs. 192 and 194); the gland is then distinctly grape-like and the follicles lie mostly in the cortical layer.
Fig. 194.—Part of a transverse section through a proglottis of Dibothriocephalus latus. Ct., cuticle; C., cirrus; Vvs., vitelline follicles; L.M., longitudinal muscles; T., testicles; M., medullary nerve; S.c., subcuticle; T.m., transverse muscles; Ut., uterus. 20/1.
The egg cell that has been fertilized and supplied with yolk cells receives the shell material at the point of entry of the shell gland ducts, and, as a complete egg, then moves onward to the uterus. In those cases in which the uterus in its further course presents a convoluted canal, and may form a rosette (pseudo-phyllidea), there is an external opening which is usually separate from the genital pore, and lies on the same or the opposite surface. In all other cases, however, the uterus terminates blindly and is represented by a longer or shorter sac lying in the longitudinal axis (fig. [191]), but in many forms transversely. With the accumulation of eggs it becomes modified in various ways: (1) it sends out lateral branches (fig. [241]), or (2) forms numerous isolated sacs (PARENCHYMAL CAPSULES) containing single eggs or groups of eggs (fig. [217]); further, (3) in some cases at the blind end one or more special thick-walled cavities are formed (PARUTERINE ORGANS or UTERINE CAPSULES), in which all or most of the eggs are collected, the uterus then undergoing atrophy.
In species in which the uterus lacks an opening, simultaneously with the growth of this organ an atrophy of the male apparatus, at least of the testes and their excretory ducts, takes place; this atrophy also frequently occurs in the female glands, so that the entire mature segments have besides the uterus only traces of the genitalia left.