Shell thick, with short spire, last whorl large and canal short; aperture wide; operculum horny.
If a distal pore or aperture is present, it is excretory in function; suck varieties have been termed " cystons " by Haeckel.
Aperture, which was mounted according to Airy's designs and under his superintendence, although the erection was not completed until after his removal to Greenwich in 1835.
Aperture evoked the comment in his journal for that year, "There is not now a single person employed or instrument used in the observatory which was there in Mr Pond's time"; and the transformation was completed by the inauguration of spectroscopic work in 1868 and of the photographic registration of sun-spots in 1873.
In some cases while the original aperture remains undivided, the seminal groove is closed and so converted into a canal.
In this category are included (by Goodrich and Lankester) the gonad ducts of the Oligochaeta, certain funnels without any aperture to the exterior that have been detected in Nereis, &c., funnels with wide and short ducts attached to nephridia in other Polychaeta, gonad ducts in the Capitellidae, the gonad ducts of the leeches.
Terrestrial and usually littoral; genital duct monaulic, the penis being connected with the aperture by an open or closed groove; shell with a prominent spire, the internal partitions often absorbed and the aperture denticulated.
41, B), where, however, the tentacles have quite disappeared, and the circular rim formed by the margin of the umbrella has nearly closed over the manubrium leaving only a small aperture through which the embryos emerge.
The medusae In such a system the dactylo- 'gastropore, so that the entire single aperture subdivided by FIG.
Shell trochiform, with canaliculated aperture and twisted columella.
' Shell globular and ventricose; aperture oval and canaliculated; operculum spiral.
Shell turriculated, with numerous whorls; aperture and operculum oval; eyes at summits of tentacles; siphon long.
In the most primitive condition the genital duct is single throughout its length and has a single external aperture; it is therefore said to be monaulic. The hermaphrodite aperture is on the right side near the opening of the pallial cavity, and a ciliated groove conducts the spermatozoa to the penis, which is situated more anteriorly.
In front of the osphradium is the single genital pore, the aperture of the common or hermaphrodite duct.
Cephalic shield bifid posteriorly; margins of foot slightly developed; genital duct diaulic; visceral cornmissure streptoneur ous; shell thick, with prominent spire and elongated aperture; a horny operculum.
Cephalic shield broad, thick and simple; shell wholly internal, thin, spire much reduced, aperture very large.
The ctenidium is atrophied, and the edge of the mantle-skirt is fused to the dorsal integument by concrescence, except at one point which forms the aperture of the mantle-chamber, thus converted into a nearly closed sac. Air is admitted to this sac for respiratory and hydrostatic purposes, and it thus becomes a lung.
The shell of the Pulmonata, though always light and delicate, is in many cases a well-developed spiral " house," into which the creature can withdraw itself; and, although the foot possesses no operculum, yet in Helix the aperture of the shell is closed in the winter by a complete lid, the " hybernaculum," more or less calcareous in nature, which is secreted by the froot.
Shell ovoid, with short spire, wide aperture and folded columella; inferior pallial lobe thick; visceral commissure still twisted.
Shell thin, dextral, with prominent spire and oval aperture; no inferior pallial lobe.
Visceral mass and shell sinistrally coiled; shell thin, with narrow aperture; no inferior pallial lobe.
Shell external, with elongated spire and numerous whorls, aperture generally narrow; male genital duct without multifid vesicles.
Shell oval, elongated, with narrow aperture; neck very long; labial palps prominent.
The inner membrane is continuous with the wall of the hollow thread at a spot immediately below the aperture in the outer wall, so that the thread itself (f) is simply a hollow prolongation of the wall of the inner capsule inverted and pushed into its cavity.
The spores escape generally by means of a distinct aperture which appears in the top of the ball.
More usually, and indeed in nearly every other case among the Oligochaeta and Hirudinea, the coelomic aperture of the nephridium consists of several cells, ciliated like the nephridium itself for a greater or less extent, forming a funnel.
I, Aperture connecting the small sac with the pericardium.
K, Aperture connecting the large sac with the pericardium.
I I.-Liotiidae, shell globular, margin of aperture thickened.
H, Left (archaic right) aperture of nephridium.
R', Aperture of the nephridium.
Shell with medium spire, external or partly covered by the mantle; genital aperture below the right posterior tentacle; genital apparatus generally provided with a dart-sac and multifid vesicles.
Swollen, aperture oval with a simple border; radular teeth in.
Internally this glandular sac presents a second slit or aperture which leads into the pericardium (as is now found to be the case in all Mollusca).
As contrasted r', Aperture of the neph with the Aspidobranchia, we find that in ridium (kidney).
The aperture, which was formerly supposed to be an aquiferous pore, leads into an extensive and often ramified cavity surrounded by glandular tubules.
Shell depressed, with rounded aperture; cephalic tentacles long.
Shell elongated; aperture expanded; siphon very short.
Shell ventricose,with elongated aperture, and short spire; proboscis and siphon long;operculum with marginal nucleus.
Shell ventricose, with short spire, and wide aperture; no varices and no operculum; foot very broad, with projecting anterior angles; siphon long.
Shell fusiform and solid, aperture elongated, columella folded; no operculum; eyes on sides of tentacles.
Shell ventricose, thin and smooth, with wide aperture; foot large and thick, without operculum.