Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0201clau Year: 1884 PTEROPODA. 55 which the arteries open. The blood returns from the lacuna? through the respiratory organs to the pericardia! sinus, whence it enters the auricle through the venous ostium. The respiratory organs, as far as they are not represented by the whole integument (Clio], have the form either of foliaceous branchial appendages (Pneumodermon) at the hind end of the body, or, in the shell-bearing forms, of internal gills placed within the mantle cavity, the entrance to which is lined
Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0201clau Year: 1884 PTEROPODA. 55 which the arteries open. The blood returns from the lacuna? through the respiratory organs to the pericardia! sinus, whence it enters the auricle through the venous ostium. The respiratory organs, as far as they are not represented by the whole integument (Clio], have the form either of foliaceous branchial appendages (Pneumodermon) at the hind end of the body, or, in the shell-bearing forms, of internal gills placed within the mantle cavity, the entrance to which is lined with peculiar ciliated bands. The gills are always but slightly developed, and are reduced either to folded elevations of the ciliated mantle-wall, or to the mantle-wall itself. The kidney is an elongated contractile sac, which communicates with the pericardia! sinus by a ciliated funnel, and with the mantle cavity or directly with the exterior by a strongly ciliated opening which is capable of being closed. The nervous system resembles that of the higher Opisthobranchs. Pleura! ganglia are present. The cephalic cones receive their nerves from the brain ; the two fins as parts of the foot from the pedal ganglia. Sense organs.—A pair of auditory vesicles are always present. Eyes on the other hand are absent or very rudi- FlG- of Cavoimia tride J tuta (after Fol). Ms, velurn ; ] mentary, as red pigment spots (Hyalea.) placed either on the visceral sac' near the oasophageal ring or on the tentacles (Clio). Tactile organs are represented by two small tentacles (Hyalea, Cymbulia] and the larger cephalic cones which are some- times beset with suckers (Clio and Pneumodermon}. The Pteropoda are hermaphrodite. The hermaphrodite gland lies near the heart behind the stomach in the visceral sac, and usually possesses a common duct which is provided not only with a seminal vesicle, but also with a kind of albumen gland and receptaculum seminis; it opens to the exterior usually
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