. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. 434 BULLETIN OF THE. Diagrammatic Sketch of different Forms of the Ctenidia in Mollusks. The length of the filaments or lamella; in the first five figures of the diagram is made for convenience disproportionally small. A. Cross-section of gill of Dimya, showing large blood-vessel in the stem, and the position occupied by the filaments upon the stem. B. Cross-section of the gill in Amusium Dalli, the filaments touching but not organically united above. C. The same of Area ectocomata, showing the tubular filame
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. 434 BULLETIN OF THE. Diagrammatic Sketch of different Forms of the Ctenidia in Mollusks. The length of the filaments or lamella; in the first five figures of the diagram is made for convenience disproportionally small. A. Cross-section of gill of Dimya, showing large blood-vessel in the stem, and the position occupied by the filaments upon the stem. B. Cross-section of the gill in Amusium Dalli, the filaments touching but not organically united above. C. The same of Area ectocomata, showing the tubular filaments planted in a groove, and the asymmetrical position of the blood-vessels. D. Section of gill in Area Noce, the filaments organically united. E. The same for Janira hemicyclica. F. Cross-section of one of the gills of Pleurotomaria Adansoniana. G. Gill in Cardium sp. H. Cross-section of the left pair of gills in Perna epJiippium ; at a these are united with the right-hand pair by connective tissue crossing the median line of the animal. 1. Cross-section of the gill in Nucula, after Mitsukuri. Dimya we have the still simpler form of a stem with only a single series of filaments. (See Diagram A.) In Amusium Dalli we have a gill of the form described by Prof. Huxley. The stem has two series of filaments, which are organically connected only at their bases, one series attached on each side of the stem with the space between them slightly excavated, and the lumen of the blood-vessel below it of a semilunar shape. (See Diagram B.) The filaments, as in Dimya, are adhesive to one another wherever they touch, have hoof-shaped extremities, and are supported by fine chitinous rods, one to each filament. In the ordinary shallow-water Pectens (e. g. Janira hemicyclica, see Diagram E) there are on each side of the stem two series of filaments, organically con- nected by delicate tissue, sustained by rods of chitine, and forming a double series on each side of the stem. These series do not
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