. A text-book of invertebrate morphology. Invertebrates. 316 INVERTEBRATE MORPHOLOGY. usually brilliant coloration. The foot in the pelagic Phyl- lirJioe has entirely disappeared, but is usually elongated and provided with a broad flat surface, in accordance with the creeping habits of the Nudibranchs. Parapodial folds, such as occur in the Tectibranchs, are never developed. Order Pulmonata. The Pulmonates differ from all the other groups of Gas- teropods in that they are, with the exception of a single genus, Onchidium, either terrestrial or aquatic; and in adaptation to this assumed habit ce
. A text-book of invertebrate morphology. Invertebrates. 316 INVERTEBRATE MORPHOLOGY. usually brilliant coloration. The foot in the pelagic Phyl- lirJioe has entirely disappeared, but is usually elongated and provided with a broad flat surface, in accordance with the creeping habits of the Nudibranchs. Parapodial folds, such as occur in the Tectibranchs, are never developed. Order Pulmonata. The Pulmonates differ from all the other groups of Gas- teropods in that they are, with the exception of a single genus, Onchidium, either terrestrial or aquatic; and in adaptation to this assumed habit certain well-defined changes have occurred. In some genera, more especially the aquatic forms, such as Zimncea, PJiysa, and Planorhis, the visceral hump has its typi- cal Gasteropod development, and is spirally coiled; but in many terrestrial forms, such as Limax (Fig. 142, A), Arion, and Vaginula, it is low and elon- gated parallel to the long axis of the foot with which it is fused. The mantle is in all forms well developed, but pre- sents the peculiarity that it is fused by its edges to the body- wall except at one point upon the right side, where an open- ing is left by which the other- wise completely-closed mantle- cavity communicates with the exterior and through which air may be taken into the cavity. The position of the mantle- cavity, when not interfered with by secondary changes, is upon the right side of the body and somewhat in front of the visceral hump when this is present. A spirally-coiled shell is present in all forms in which the visceral hump is well developed, as in Limncea, Physa, Helix (Fig. 142, B), and Planorhis, but in the elongated terrestrial forms a rudimentation of the shell accompanies the diminution of the visceral hump. Thus in Daudehardia, in which only a slight trace of the hump persists, the shell has become. Pig. 143.—A, Limax maximus; B, Helix (after Howes).. Please note that these images are extracted from scanned page images that may have
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyo, bookyear1894
