662 THE ANIMAL KINGDOM. 



phyllidea except Triaenophorus. The aperture of the cirrus into the 

 sinus genitalis usually lies in front of, or anteriorly to, that of the vagina, 

 but in some of the Taeniae with narrow joints the two apertures are side 

 by side, e.g. in T. perfoliata *. In Schistocephahts and Ligtda the male and 

 female apertures are ventral, but there is no sinus ; the uterus opens near 

 to them and all three apertures are in the adult disposed in, a straight line 

 crosswise, but not always in the same order from right to left. The uterus 

 of Bothriocephahis opens posteriorly to the genital sinus, of Triaenophorus 

 anteriorly, and, unlike its genital ducts, on the surface of the joints. 



Self-impregnation appears to be common if not universal ; indeed, 

 there does not appear to be the slightest evidence for the fertilisation of 

 one joint by another ; and if such an occurrence happens, it must take 

 place by the accidental contact of individuals inhabiting side by side the 

 same host 2 . The egg is composed of two sets of elements the germ-cell 

 derived from the germarium, and the vitellogenous cells or the secretion 

 derived from the vitellarium. The germ-cell is nucleated and hyaline as a 

 rule. In Leuckartia and Abothrmm it is said to absorb the vitelline 

 granules set free by degeneration of the vitellogenous cells, but in other 

 instances the latter appear either to retain their integrity or else break 

 down as in the Taeniae into a more or less granular albumen. The germ 

 is impregnated, and together with the vitelline cells or secretion enters the 

 uterus where it is surrounded by a shell, the material of which appears to 

 be derived from Mehlis' gland (supra\ inasmuch as the latter reaches its 

 greatest development at the time when germs enter the uterus. The shell 

 is delicate in the Taeniae and where the embryo is formed during the 

 sojourn of the ova in utero, but resistent and furnished with an operculum 

 where as in some species of Bothriocephalus, in Schistocephalus, Triaeno- 

 phorus, and Ligula, it lies in water for a shorter or longer period. The 

 shell is sometimes furnished with processes, e. g. in Calliobothrium Esch- 

 richti, which however appear in Taeniae to be accidental formations. The 

 ova of certain fish tapeworms turn green or black on exposure even for a 

 few moments to light. The embryo is formed by the fission of the germ- 

 anteriorly to the cirrus ; (3) the uterus at a certain period convoluted ; (4) a peculiar shell-gland 

 (supra) ; egg-shell hyaline, ovate as in Pseudophyllidea. In all four points it differs from a typical 

 Taenia. Cf. Zschokke on sexual organs of T. litterata from the Fox, Z. A. viii. 1885. 



1 Van Beneden in his Vers Cestoides sometimes figures the cirrus of fish tapeworms as posterior 

 to the vagina. Leuckart states that this is an error so far, at least, as concerns the genus 

 Tetrarhynchus. 



a The cirrus has been observed in the vagina of the same joint in Taenia Echinococcus by 

 Leuckart ; in Phyllobothrium Lactuca by P. J. van Beneden, who witnessed the emission of sperm. 

 ' Depuis/ adds the latter, 'j'ai vu ce phenomenese reproduire dans d'autres especes' (Vers Cestoides, 

 p. 64). Sommer states that in T. mediocanellata the sperm passes into the sinus genitalis, and 

 regurgitates into the vagina owing to the closure of the pore. The protrusion of the cirrus hinders 

 impregnation in this case (Z. W. Z. xxiv. 1874, pp. 520-21). See also Moniez on T. Giardi, C. R. 

 Ixxxviii. 1879. 



