. Elements of Comparative Anatomy. . the hermaphrodite A Of Helix horten- generative gland is, moreover, always unpaired, and is placed, and opens, asymmetrically, so that, as compared witli the Lamellibran- chiata, it must have undergone unilateral degeneration. The hermaphrodite gland varies greatly in character. It is always made up of a number of lobes (Fig. 203, A), which form the ovarian germs at their furthermost blind ends (ffl), while the seminal masses are developed at some distance from the end (b). These spots are not, however, separated from one another, but the common cavity of a
. Elements of Comparative Anatomy. . the hermaphrodite A Of Helix horten- generative gland is, moreover, always unpaired, and is placed, and opens, asymmetrically, so that, as compared witli the Lamellibran- chiata, it must have undergone unilateral degeneration. The hermaphrodite gland varies greatly in character. It is always made up of a number of lobes (Fig. 203, A), which form the ovarian germs at their furthermost blind ends (ffl), while the seminal masses are developed at some distance from the end (b). These spots are not, however, separated from one another, but the common cavity of a lobule is the spot at which the various pro- ducts are developed. They are, therefore, cells derived from epithelial structures, which become ova at one point, and at another give rise to seminal filaments. This double production does not seem to take place simultaneously, as a rule, so that the same lobule or the same gland produces ova at one time, and sperm at another. A differentiation may be made out in the lobules when the ovarian portions form diverticula (B, a) ; in this case they are grouped in a rosette around the seminal portion {h), and have the appearance of secondary acini. The variations in the forms of the hermaphrodite gland are due to the way in which the separate lobules are united together; thus each lobule may have its proper duct, and the whole gland look like a greatly-ramified organ (Opis- thobranchiata); or the acini may open in a row on one side of a duct, as in some Pteropoda (Cymbulia, Tiedemannia); or they may be grouped into racemose or lobate masses of glands, of which there may be a number (Phyllirhoe), or they may form a single, more or less compact, gland (some Pteropoda, as PneumodermoUj Hyalea ; most of the Opisthobranchiata and Pulmonata). Fig. 203. Follicles of glands of Gastropoda. sis. The ova {aa) are developed on the wall of the follicle ; and the seminal masses (h) internally. B Of Aeolidia. The seminal portion (b) of a follicle is be
Size: 1459px × 1712px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bo, bookcentury1800, bookdecade1870, bookpublisherlondonmacmillan
