. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). glossate u forms, , have a wautiug tX/J \jy VU* l1 couse- najority itrial iu ' life are Iu Am- }io7na ; D, 11 a com- Id of the sels and so that »ecies of I'restrial, rely ter- :)M beiiij4 I of the a creeji- 5up pre- or it the nbers of aninials, Sereuces TYPE MOLLUSCA. 309 from the other Mouotocardia, while others are extensively modified. The gemis Atalanta possessc a large transparent shell within which the animal can be completely retracted. The foot is no longer adap
. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). glossate u forms, , have a wautiug tX/J \jy VU* l1 couse- najority itrial iu ' life are Iu Am- }io7na ; D, 11 a com- Id of the sels and so that »ecies of I'restrial, rely ter- :)M beiiij4 I of the a creeji- 5up pre- or it the nbers of aninials, Sereuces TYPE MOLLUSCA. 309 from the other Mouotocardia, while others are extensively modified. The gemis Atalanta possessc a large transparent shell within which the animal can be completely retracted. The foot is no longer adapted for creeping, but is differenti- ated into a laterally flattened keel-like pro- and mesopodium which bears a sucker on its posterior surface, and a metapo- dium provided with an operculum. Iu Carinaria (Fig. 138). Fig. 138.—Stuuctuke of Carinaria mediteiranea (after Owen). ao = aoitii. b = buccal mass. eg = cerebral gangliou. ct = ctenidium. h = liL'ait,. i= intestine. I = liver. mp = iiusopodiuni. 0 = eye. p = penis. peg = pedal ganglion. s = salivary gland. su = sucker. te = t estis. I'd = vas deferens. vg = visceral ganglion. m = seminal vesicle. the visceral hump is reduced to a comparatively small mass upon the dorsal surface of the elongated body and is enclosed iu a transparent shell shaped like a liberty-cap. The pro- and mesopodium have the form of a plate hanging down from about the middle of the under-surface of the body, and the metapodium is directed backwards, forming in reality the posterior portion of the body. The same relationships of the foot are found in Pterotrachen, which presents the extreme of modification found iu this grou]) ; in this form the visceral liump is still more reduced than in (hrimma, forming only a small oval mass imbedded in tlie dorsal surface of the body and being destitute of any shell. Considering these two forms. rrl ?»'. Please note that these images are extracted from scanned page images that may have been digitally enhan
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