. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). TYPE MOLLUSCA. 301 commissures, recalling the condition seen in the Chitons, as well as the ladder-like arrangement of the ventral nerve-cords of the Annelida, though there cannot in the Gasteropods be any question of metamerism in this connection. Special sense-organs are very generally well developed in the Gasteropods, The tentacles so usually found upon the head have probably a tactile function as well as the tentacular or winglike processes sometimes found in conne
. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). TYPE MOLLUSCA. 301 commissures, recalling the condition seen in the Chitons, as well as the ladder-like arrangement of the ventral nerve-cords of the Annelida, though there cannot in the Gasteropods be any question of metamerism in this connection. Special sense-organs are very generally well developed in the Gasteropods, The tentacles so usually found upon the head have probably a tactile function as well as the tentacular or winglike processes sometimes found in connection with the anterior extremity of the foot, and the epipodial ten- tacles Avhich occur in some forms {llaliotis). On the ventral side of the bases of the epipodial tentacles of some forms s})ocial sensory thickenings have been found which havt^ suggested a compariscm with the sense-organs of the lateral line of the Annelida, a comparison which, however, at present seems rather strained ; it seems probable, notwithstanding their innervation from the pedal ganglia, that these sensory })atches are to be placed in the same category as the osphra- dia and the sensory ridges of the mantle-cavity of the Chi- tons. Tlie osphradia (Fig. 188, os) in all Gasteropods which are provided with branchiie are associated with these "igans' and even where one or both -mi^J^ branchiio have been suppressed the osphradia may still persist. Eyes (Fig. 134) are very generally j)resent in the Gasteropods, being situated at the base of tlie ten- tacles, or at tlieir summit in some forms. Tiiey present a veiy uni- form structure throughout the group and arise as a depression of tin; integument, the lips of the cavity fusing and giving rise to a glol)uhir sac lying beneath th(i ejiidermis, which I'emains thin and transparcmt, forming an outer i-ornea U'\ I'he cells of the outer wall of tlie sa lemaindtu" of the wall of the sac they are sensor) in function, ]>igniented cells being scatter
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyo, bookyear1896
