. The depths of the ocean; a general account of the modern science of oceanography based largely on the scientific researches of the Norwegian steamer Michael Sars in the North Atlantic. Oceanography. 598 DEPTHS OF THE OCEAN CHAP. life fix themselves to the bottom and become sessile, like the Hydro- medusae, forming colonies by budding. They are thus meropelagic, whereas all other Tunicata are holopelagic and perfectly independent of the bottom. These latter are the only ones to be dealt with here, viz. Appendicularians, Salpae, and the genera Doliolum and Pyrosoma. The Appendicularia resemble
. The depths of the ocean; a general account of the modern science of oceanography based largely on the scientific researches of the Norwegian steamer Michael Sars in the North Atlantic. Oceanography. 598 DEPTHS OF THE OCEAN CHAP. life fix themselves to the bottom and become sessile, like the Hydro- medusae, forming colonies by budding. They are thus meropelagic, whereas all other Tunicata are holopelagic and perfectly independent of the bottom. These latter are the only ones to be dealt with here, viz. Appendicularians, Salpae, and the genera Doliolum and Pyrosoma. The Appendicularia resemble greatly the larvae of Ascidians, and present a remarkable likeness to early vertebrate types. As a rule they are trans- parent and perfectly devoid of colour. Their body (see Fig. 445) is clumsy in shape and contains all the organs of nutrition and propagation, with a long elastic tail which serves solely the purpose of locomotion. Lohmann has studied the biology of this group,1 and his results will be referred to later. if The Appendicularians live mostly in the upper 200 I / metres of the ocean, though in tropical waters they occur deeper ; in fact in the Sargasso Sea the German Plankton Expedition found more of them below than above 200 metres. As with most sur- face forms the species are most abundant in warm waters, like Appendicularia sicula, Fritillaria venusta, and Oikopleura parva, while Oikopleura vanhoffeni and O. labradoriensis are northern forms. The Salpae are free-swimming, barrel-shaped, transparent animals, well-known to all sea-faring people (Fig. 446). They are often seen crowding the surface-waters of the ocean in countless num-. Fig. 445. Oikopleura labradoriensis, Lohm (about \°). (From Lohmann.) Valdivia bers. Among investigations of recent years we may cite the report on the " Valdivia " collection by In hauls with closing nets the found the majority of Salpae in depths less than 200 Please note that these images are extrac
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